WO2010076494A1

WO2010076494A1 - Transmission method and reception method for a piece of audiovisual content

Info

Publication number: WO2010076494A1
Application number: PCT/FR2009/052554
Authority: WO
Inventors: Patrice Houze; Christian Bertin; Julien Gloaguen
Original assignee: France Telecom
Priority date: 2008-12-16
Filing date: 2009-12-16
Publication date: 2010-07-08

Abstract

The invention relates to a method for transmitting an encoded piece of audiovisual content, in the form of a plurality of data streams, from a server (S) to a terminal (T1, T2), including a step of transmitting at least one first stream relating to the piece of content from the server in a first transmission mode, and a step of transmitting a portion of at least one second stream relating to the piece of content from the server in a second transmission mode. The two transmission steps are simultaneous and the portion of the second stream transmitted simultaneously with the first stream only relates to a portion of the end of the piece of content.

Description

Title: Method of transmission and method of receiving audiovisual content

The field of the invention is that of the transmission of audiovisual content as part of a VoD service ("Video on Demand" for "video on demand").

A video on demand (VOD) server is intended to transmit streaming audiovisual content stored on its disk to a client who has requested to view this content. To make this request, the client sends a request to the server according to a defined protocol (for example, the RTSP protocol, presented in particular in the document IETF RFC 2326, "Real Time Streaming Protocol (RTSP)", April 1998).

Depending on this request, the server can then transmit the requested content to the client.

Such data transmission servers are today heterogeneous, in the sense that they serve a plurality of clients (receiving terminals) having very different types of access to data. Thus, the global Internet network, for example, is accessible from a personal computer terminal as well.

(PC) than a radiotelephone. More generally, the bandwidth for access to the network varies greatly from one receiving terminal to another. Thus, a first customer can for example access the Internet from a powerful PC, and have an ADSL ("Asymmetric Digital Subscriber Line" for "asymmetrical digital subscriber line") to 1024 kbits / s while a second client is trying to access the same data at the same time from a terminal type

PDA ("Personal Digital Assistant") connected to a low-speed modem.

Hierarchical image coding algorithms (or "scalable" in English) have been developed, allowing adaptable quality and variable spatiotemporal resolution. According to these techniques, an encoder generates a compressed stream having a hierarchical layered structure, in which each of the layers is added to the previous layers, the first being the base layer. For example, a first data layer carries a 256 kbit / s stream, which can be decoded by a PDA type terminal, and a second complementary data layer conveys a 256 kbit / s stream which can be decoded, in addition to the first, by a more powerful PC-type terminal. The rate required for the transport of these two layers is in this example 512 kbit / s.

Such coding algorithms are thus very useful for all applications for which the generation of a single compressed stream organized in several hierarchical layers can serve several clients of different characteristics.

SVC ("Scalable Video Coding") MPEG-4 ("Moving Picture Expert Group") video compression standard, (ITU-T Recommendation H.264 (11/2007),

Advanced video coding for generic audiovisual services, ISO / IEC 14496-10: 2008,

Information technology - Coding of audio-visual objects - Part 10: Advanced video coding.), Developed jointly by the ITU ("International Telecommunication Union" for "International Telecommunication Union") and ISO (International Organization for Standardization "for "International Standards Organization") specifies such hierarchical coding.

During a request from a terminal, the server then determines the number of layers that can be transmitted as a function of the rate of the line and then transmits these layers in as many streams according to a streaming mode (streaming mode for example) without use all available throughput of the link.

In the case where the rate of the line is less than the overall rate of the content, the quality of the image received by the terminal is degraded.

The current technique does not allow to transmit continuously, therefore in real time, non-degraded images when the bit rate of the line is lower than the overall rate of the content.

There is therefore a need to receive and display in real time audiovisual content containing good quality images with a line rate lower than the overall rate of content.

For this purpose, the present invention proposes a method for transmitting an audiovisual content coded in the form of a plurality of data streams, since a server to a terminal, comprising a step of transmission by the server of at least a first stream relative to the content according to a first transmission mode, characterized in that it further comprises a step of transmission by the server of a part of at least a second stream relative to the content according to a second transmission mode, the two transmission stages being simultaneous and said part of the second stream transmitted simultaneously to the first stream being relative to only a part of the end of the content.

Thus, according to the invention, at least a first stream and a part of a second stream are transmitted in parallel to a receiving terminal: the first stream is transmitted according to a first transmission mode, for example in "streaming" mode (c). ie, continuously or in real time), and the part of the second stream is transmitted according to a second transmission mode, for example in "download" mode. The part of the second non-priority stream, transmitted according to the second transmission mode, uses the available bandwidth, unused for the transmission of the first stream.

The first stream may be requested by the receiving terminal in a real-time request. The remaining bandwidth is used to transmit the second stream for download. The download mode is a flow control mode in which the transmission server waits for an acknowledgment of the terminal to continue the transmission. This transmission mode thus makes it possible to adapt the rate of sending the data packets to the remaining bandwidth.

Of course, it could be envisaged that several streams are transmitted according to the first transmission mode and / or that several streams are transmitted according to the second mode of transmission. The first stream may be a priority basic stream, corresponding to a standard quality of the content, and the second stream to an enhancement stream to improve the quality of the content. Only a portion of the enhancement stream stored in the server, corresponding to an end portion of the content, is transmitted at the same time as the first stream. Thus, the invention enables the transmission in real time of a content whose image quality is improved. -AT-

during the restitution of an end part of the content.

Advantageously, this method makes it possible to use previously coded streams and does not require a new coding of these streams.

In a particular embodiment, there is provided a step of determining by the server of said at least one first stream to be transmitted according to the first transmission mode and said at least one second stream, part of which is intended to be transmitted according to the second mode. according to information relating to a bit rate of a transmission line to the terminal and information relating to the bit rates of the streams coding the content. As a function of the bit rate of the transmission line of the terminal, on the one hand, and the bit rates required for the transmission of the streams coding the content, on the other hand, the server can identify, among all the streams encoding the content, the stream or streams that can be transmitted in full according to the first transmission mode , and the stream or streams that can be transmitted partially according to the second transmission mode. According to a particular embodiment, the first transmission mode is a continuous mode according to a first timing and the second transmission mode is a continuous mode according to a second timing, said second timing being defined by a step of calculating the transmission times of packets of the second stream. This embodiment is particularly suitable in the case where it is the server that identifies the stream or streams to be transmitted according to the first transmission mode and the stream or streams to be partially transmitted according to the second transmission mode.

In the case of a content coded according to a basic stream and enhancement streams, the server may for example transmit the base stream in real time and, after having determined the portion of a transmitting stream that can be transmitted, adapted the rate of sending the data packets of this stream according to the flow remaining available.

According to a particular embodiment, another part of said at least one second stream, relating to a start portion of the content, is transmitted before the start of the simultaneous transmission of said first stream according to the first transmission mode and said part of said second flow according to the second mode of transmission.

Thus, elements for further improving the quality of the displayed stream are transmitted before the transmission of the actual stream. Since the volume of transmitted elements is small, since only a portion of the enhancement flux is transmitted, the flow display is only slightly delayed.

In a particular embodiment, the audiovisual content is encoded as a base stream and at least one enhancement stream and the at least one first stream stream comprises the base stream.

The invention is thus adapted to the transmission of SVC type content. In another embodiment, the audiovisual content is encoded as a constant rate stream and a variable rate stream, said at least a first stream comprises the constant rate stream.

The invention is thus adapted to the transmission of VBR type contents.

The invention also relates to a method of reception by a terminal of audiovisual content coded in the form of a plurality of streams and transmitted by a server, comprising a step of receiving at least a first content-related stream transmitted according to a first reception mode, characterized in that it further comprises a step of receiving a portion of at least a second stream relative to the transmitted content according to a second transmission mode, the two reception stages being simultaneous and said portion of the second stream received simultaneously to the first stream being relative to only one end portion of the content.

In a particular embodiment, the method comprises

a step of storing the part of the second stream received according to the second mode of transmission,

a step of interleaving the stored portion of the second stream and the first stream, from a time corresponding to the beginning of said end portion of the content, and

a step of decoding and displaying the interlaced stream.

For example, in parallel with a stream received in real time, the terminal receives and stores a portion of a stream received according to a second mode of transmission such as a mode download. At first, only the real time stream is displayed. Then, from a given moment, the part of the stream received according to the second transmission mode is interleaved with the real time stream, thereby improving the quality of the images displayed. The given instant is calculated in such a way that the improvement of the flow continues until the end of the display of the content.

In a particular embodiment, another part of the second stream, relating to a start portion of the content, is received before the start of the simultaneous reception of the first stream according to the first transmission mode and said part of the second stream according to the second mode of transmission. This embodiment makes it possible to obtain an improvement in the image quality during the entire duration of display of the content. The display delay generated by the transmission of a part of the second stream before the transmission of the first stream is small insofar as the amount of information thus transmitted is of reduced volume. According to a particular embodiment of the invention, the reception method further comprises a step of constructing a stream flow transmission request of the first stream and a stream flow transmission request of said part of the stream. second stream, subsequent to a predetermined stream pointer.

The invention also relates to a server capable of transmitting audiovisual content, said content being coded according to a plurality of data streams, to a terminal, comprising first transmission means adapted to transmit at least a first content-related stream according to a first mode of transmission, characterized in that it further comprises second transmission means adapted to transmit a portion of at least a second stream relative to the content according to a second transmission mode simultaneously with the transmission of the first stream according to the first transmission mode, said part of the second stream being relative to only a part of the end of the content.

The invention also relates to a terminal able to receive an audiovisual content encoded in the form of a plurality of streams, via a transmission line, comprising stream transmission request means, reception means, a first group of streams of the plurality of streams transmitted in a first transmission mode, means for decoding and displaying in real time said received first group of streams, characterized in that it further comprises:

means for receiving, in parallel with the reception of the first group of streams, a part of a second group of streams of the plurality of streams transmitted according to a second mode of transmission, said part being located after a predetermined pointer of the second group of flows;

means for storing said part of the second group of streams received;

means for interleaving the stored flow and the first flow group; and in that the decoding and display means are able to decode and display the interlaced stream.

According to one embodiment, the terminal for receiving audiovisual content encoded in the form of a plurality of data streams, comprising first means for receiving at least a first content-related stream transmitted according to a first mode of transmission. transmission, characterized in that it further comprises second receiving means adapted to receive a portion of at least one second stream relative to the transmitted content according to a second transmission mode and simultaneously to the first stream, said part of the second stream being relative to only a part of end of the content. The invention also relates to a system comprising a server as defined above and at least one terminal as defined above.

The invention also relates to a computer program product comprising instructions for implementing the steps of a transmission method as defined above and / or a reception method as defined above when it is loaded and executed by a user. processor.

Other features and advantages of the present invention will appear in the following description of embodiments given by way of non-limiting example, with reference to the accompanying drawings, in which:

FIG. 1 is a general diagram presenting the context of the invention; FIG. 2a is a diagram illustrating an example of audiovisual content; composed of 4 streams,

FIG. 2b is a diagram illustrating the transmission, as a function of time, of the streams of audiovisual content presented in FIG. 2a, according to a first embodiment, FIG. 2c is a diagram illustrating the display of the streams of audiovisual content. presented in FIG. 2a, as a function of time, according to a first embodiment,

FIG. 3 is a flowchart illustrating the various steps of a method for transmitting audiovisual content according to a first embodiment of the invention,

FIG. 4 is a flowchart illustrating the various steps of a method for receiving audiovisual content according to a first embodiment of the invention,

- Figure 5 is a block diagram showing a terminal adapted to implement the receiving method according to the first embodiment.

FIG. 6 is a flowchart illustrating the various steps of a transmission method and a reception method according to a second embodiment,

FIG. 7a is a diagram illustrating the transmission, as a function of time, of the fluxes of the audiovisual content presented in FIG. 2a, according to a second embodiment,

FIG. 7b is a diagram illustrating the display of the streams of the audiovisual content presented in FIG. 2a, as a function of time, according to a second embodiment; FIG. 8a is a diagram illustrating an example of audiovisual content recorded under FIG. form of 3 streams,

FIG. 8b is a diagram illustrating the transmission, as a function of time, of the streams of the audiovisual content presented in FIG. 8a, according to a third embodiment; FIG. 8c is a diagram illustrating the display of the streams of audiovisual content; shown in FIG. 8a, as a function of time, according to a third embodiment,

FIG. 9 is a flowchart illustrating the various steps of a transmission method and a method for receiving audiovisual content according to a third embodiment of the invention,

FIG. 10 is a block diagram showing a device able to perform the steps of a transmission configuration method according to one embodiment of the invention,

- Figure 11 is a block diagram showing an example of a terminal adapted to perform the steps of a reception method according to one embodiment of the invention.

With reference to FIG. 1, a SYS system comprises a server S and one or more terminals T1, T2, T3. Terminals T1, T2, T3... Are capable of communicating with the server S via a transmission line. a telecommunication network.

The server S is for example a computer.

The terminal T1 is for example a mobile terminal able to communicate with the server S via a transmission line L1, for example of the GSM type.

The terminal T2 is for example a computer type PC (for "Personal Computer") able to communicate with the server S via a transmission line L2, for example of the RTC type (for "switched telephone network").

The terminal T3 is for example a PC type computer capable of communicating with the server S via a transmission line L3, for example of the ADSL type (for "Asymmetric Digital Subscriber Line"). The server S has a memory MEM in which audiovisual contents C1, C2, etc. have been stored. Each audiovisual content is recorded in the form of at least two files: a so-called "basic" file and one or more so-called files. "raising". The base file contains basic content, compressed and encoded so that it can be transmitted in streaming mode, ie in real time mode, to most terminals. The enhancement file (s) contain compressed and encoded information to improve the display quality of the basic content.

With reference to FIGS. 2 to 5, a first embodiment of a transmission configuration method, a transmission method and a method for receiving audiovisual content according to the invention will now be described.

In this embodiment, a user of the terminal T1 controls the transmission of the content C 1.

As illustrated in FIG. 2a, the audio-visual content Cl is stored in the form of four files coded in SVC (for "Scalable Video Coding"): a file CB containing a base stream coded at a bit rate DB1, for example

500 Kbps,

a first file CRl containing a first enhancement stream coded at a bit rate DR1, for example 150 Kbits / s,

a second file CR2 containing a second enhancement stream coded at a bit rate DR2, for example 100 Kbits / s,

a third file CR3 containing a third enhancement stream coded at a bit rate DR3, for example 50 Kbits / s.

As an alternative, the content Cl contains a different number of enhancement streams. As an alternative, the audiovisual content C 1 is stored in the form of files coded in VBR (for "Variable Bit Rate"): a file containing a constant bit rate stream and one or more files accumulating the variations above this constant flow.

The configuration of the transmission of audiovisual content C1 and the transmission of this content C1, according to a particular embodiment of the invention, will now be described with reference to FIG.

During a first step E2, the terminal T1 transmits to the server S via the transmission line L1, a request RQ1 for requesting the audiovisual content C1. The request RQ1 includes an identifier of the audiovisual content C1, for example the code ISAN (International Standard Audiovisual Number) of a movie. The contents audiovisual Cl is, for example, chosen by the user from a list of available contents transmitted to the terminal Tl by the server S.

During a step E4, the server S sends the terminal T1 a response RR1 to the request RQ1. The response RR1 contains the duration TD1 of the content C1, that is to say the duration of display of the content in real time, as well as information relating to the files stored on the server S for the audiovisual content Cl. Information relating to the files stored for the audiovisual content Cl are for example:

a URL (for "Uniform Resource Locator") UBR making it possible to request the base stream CB according to a first transmission mode and the coding bit rate DB1 associated with the base file CB,

an URL UR1 making it possible to request the first enhancement stream CR1 according to a first transmission mode and a URL UT1 making it possible to request the first enhancement stream CR1 according to a second transmission mode and the coding bit rate DR1 associated with the first file; CRl enhancement,

an UR2 URL making it possible to request the second CR2 enhancement stream according to a first transmission mode and a UT2 URL making it possible to request the second CR2 enhancement stream according to a second transmission mode and the DR2 coding rate associated with the second file; CR2 enhancement,

an UR3 URL making it possible to request the third enhancement stream CR3 according to a first transmission mode and a UT3 URL making it possible to request the third enhancement stream CR3 according to a second transmission mode and the coding bit rate DR3 associated with the third file CR3 enhancement.

The first mode of transmission is for example a real time mode, for example a "streaming RTP" mode (for "Real Time Protocol").

The second mode of transmission is for example a download mode with flow control using for example the "FTP" protocol (for "File Transfer Protocol) or "HTTP" (for "HyperText Transfer Protocol").

The response RR1 is for example a content description file of the type

SDP (for "Session Description Protocol") defined by the IETF (for "Internet

Engineering Task Force ") to which a URL to request a download enhancement stream in download mode has been added for each enhancement stream of the content Cl.

During a step E6, the terminal T1 determines the rate DL1 of the transmission line L1. The method used to calculate the flow rate of the line is for example the method disclosed in European Patent EP 1578085 published on 28/11/2007.

The determined rate DL1 is for example 600 Kbps.

In the case where the rate DL1 of the transmission line L1 is greater than the sum of the coding bit rate DB1 of the base file CB and the coding bit rates DR1, DR2, DR3 of the raising files CR1, CR2, CR3, the terminal Tl can request the simultaneous transmission of the basic stream CB and enhancement streams in streaming mode. It is not necessary in this case to implement the method of the invention.

In the case where the rate DL1 of the transmission line L1 is less than the bit rate

DB1 of the basic stream CB, none of the streams of the content Cl can be transmitted in real time to the terminal T1. The content must then be transmitted conventionally in download mode (prior or progressive) for a delayed display. The method of the invention can not be implemented in this case.

If the rate of the line DL1 is greater than the coding bit rate DB1 of the base stream CB and less than the sum of the coding bit rate DB 1 of the base stream CB and the coding bit rates of the raising streams, the terminal T1 selects, during a step E8, a first group G1 of flows able to be transmitted to the terminal T1 in streaming mode.

The first group G1 contains the base stream CB and one or more enhancement streams. More specifically, the terminal T1 calculates the sum of the respective flows of the stream base and the first enhancement stream. If the calculated sum is smaller than the rate of the transmission line L1, the first enhancement stream is a stream of the first group. The terminal T1 then adds to the calculated sum the rate of the second enhancement flow; so on, until the calculated sum is greater than the rate of the line L1.

The first group G1 is thus determined as a function of the information relating to the bit rate of the transmission line and as a function of flow information of the streams coding the audiovisual content C1.

In the embodiment described here, the first group of streams G1 comprises only the base stream CB.

During a step ElO, the terminal T1 selects a second group of flows G2. The second group of stream G2 contains one or more streams of audiovisual content C1 not contained in the first group of streams Gl.

The second group G2 is determined according to the information relating to the bit rate of the transmission line and as a function of flow information relating to the streams encoding the audiovisual content C1.

In the embodiment described, the second group of flows G2 comprises only the first enhancement stream CR1.

The bandwidth or bit rate DD1 of the transmission line Ll remaining available during the transmission of the CB base stream in streaming mode is less than the coding bit rate DR1 of the first enhancement stream CR1. The raising flux CR1 of the second group of streams G2 can not be transmitted in streaming mode without loss of information.

During a step E 12, the terminal T1 determines a pointer Pl here of the first enhancement stream CR1. The pointer P1 represents the beginning of the end portion of the enhancement stream CR1 adapted to be transmitted to the terminal T1 in download mode concomitantly with the transmission in streaming mode at the terminal T1 of the base stream CB, by using the available bandwidth. . It should be noted that, in the example described here, the transmission of the base stream CB in streaming mode and the transmission of a portion of the enhancement stream CR1 in the download are intended to begin and end at the same respective times, as shown in Figure 2b. In order to determine the pointer P1, the terminal T1 first determines a quantity QI1 of information that can be transmitted in download mode during the transmission time of the base stream CB in streaming mode, which is equal to the duration TD1 of the audiovisual content. Cl, considering the remaining available bandwidth (ie not used for transmission of the CB base stream).

More precisely, the quantity of information QI1 is obtained by the formula:

QIl = TDl x DDl = TDl x (DLl- SUM (flow (s) of the flow (s) of the first flow group).

In this case, the first group of flows containing only the basic flow:

QII = TDIX (DLI-DB I)

Then the terminal Tl determines to which fraction, denoted by F (CRl), of the raising flow this quantity of information corresponds by dividing the quantity of information QI1 computed by the total amount of information of the raising flux CR1, which is equal to the duration TD1 of the content C1 multiplied by the flow CRl of the enhancement flow. In other words, the fraction F (CR1) is obtained by the formula: F (CR1) = QI1 / TD1 * DR1 = (DL1-DB1) / DR1. This calculated fraction corresponding to a proportion of the enhancement stream CR1 that can be transmitted for download during the streaming transmission of the base stream CB, using the remaining available bandwidth.

It will be recalled here that the portion of the enhancement stream CR1 corresponding to the calculated fraction of the enhancement stream CR1 to be downloaded to the terminal T1 is an end part of this stream CR1. The terminal T1 then determines the position of the pointer P1 in the enhancement stream CR1, that is to say the position of the beginning of the portion of the enhancement stream to be transmitted for download. This position of the pointer P1 in the raising flux CR1 can be represented by a fraction (1- (DL1-DB1) / DR1) of the volume or the display time of the content, defining the position of the pointer P1 from the beginning of the stream enhancement corresponding to the beginning of the content C 1. In the particular embodiment described in which the bit rate DL1 of the transmission line L1 is 600 Kbits / s, the bit rate of the DB1 basic stream of 500 Kbits / s and the bit rate of the enhancement stream DR1 of 150 Kbits / s, the fraction of the enhancement stream CR1 that can be transmitted for downloading during the streaming transmission of the basic stream is equal to (600-500) / 150 = 2/3. Consequently, the pointer P1 is at 1/3 (because 1-2 / 3 = 1/3) of the raising flux from the beginning of the raising flux CR1, in other words to the third of the first enhancement file CR1.

As an alternative, an error margin is added to the determined value P1 to prevent the real-time flow from ending before the end of the download (for example 5 or 10%).

Step E12 is followed by a step E 14 in which the terminal T1 builds a streaming RQR transmission request of the base stream CB. The RQR request contains for example the URL allowing the transmission of the base stream in streaming mode. If the first stream group G1 contained multiple streams, the RQR request could contain a URL for each stream of the group G1. Alternatively, one could generate several RQR requests.

In the embodiment described, the terminal T1 builds a request RQR containing the URL UBR. During a step E 16, the terminal T1 here constructs a request RQT for transmitting a portion of the enhancement stream CR1 in download mode. The request RQT contains the URL UTl for the transmission of the stream CRl for download and the pointer P1 determined during the step E 12. If the second group G2 of the stream contains several streams, the request RQT could contain a URL for each of the G2 group stream and an associated pointer. Alternatively, one could generate several RQT requests.

The transmission request RQR of the base flow CB and the transmission request RQT of a portion of the raising flow CR1 are then transmitted to the server S during a step E1. The server S receives the request RQR during a request. step E20 and the request RQT during of a step E22.

During a following step E24, the server S determines in the file of the raising flux CR1, a pointer P2 according to the pointer P1. The pointer P2 is for example a position in the stream file CR1 such that P2 corresponds to the pointer Pl.

Conventionally, each stream is coded as packets or data blocks. Each block comprises a header containing information relating to the moment of its decoding with respect to the beginning of the decoding of the stream. The determined pointer P2 is for example the address of a data block of the file corresponding to the pointer Pl.

The pointer P2 is optionally adjusted to correspond to the address of a data packet of the stream.

During a step E26, the server S controls, on the one hand, the transmission of the CB base stream in streaming mode (real time) and, on the other hand, the transmission of the portion of the posterior enhancement stream to the pointer P1 in download mode. .

FIG. 2b illustrates the transmission of the base stream CB during the time TD1 and the simultaneous transmission of an end portion of the first enhancement stream CR1. Both transmissions begin and end here at the same time, as shown in Figure 2b. In the embodiment described, the steps E2 to E1 correspond to the steps of one embodiment of a transmission configuration method according to the invention and the steps E20 to E26 correspond to the steps of an embodiment of the invention. a transmission method according to the invention.

A method of reception by the terminal T1 of the base stream CB and the part, subsequent to the pointer P1, of the first enhancement stream CR1 of the audiovisual content C1 transmitted by the server S in the first embodiment of a method of transmission, will now be described with reference to FIG. 4.

The terminal T1 receives blocks of data from the base stream CB (step E30) which it stores in a temporary storage memory MR of the real-time flow of the terminal T1. The terminal T1 receives in parallel, during a step E32, blocks of data of the first enhancement stream CR1 that it stores in a temporary storage memory MT of the downloaded stream of the terminal T1.

Following receipt of the first data block of the first enhancement stream CR1, the terminal T1 reads the header of the received block. The header contains, in a conventional manner, information relating to the time of decoding H1 of the block relative to the start time of the decoding of the content (that is to say the start time of the content). The terminal T1 stores the decoding time H1 in a temporary memory TEMP1 of the terminal T1, during a step E34. The decoding time H1 corresponding to the start time of the portion of the enhancement stream CR1 transmitted by the server S and received by the terminal T1.

In a next step E36, the instant H1 is compared with the current instant H of each block of the base stream CB received in real time and decoded, from the beginning of the decoding of the basic flow of the content. As long as the instant H1 is not reached by the current instant H, the terminal T1 decodes the blocks received from the basic stream CB stored temporarily in the storage memory MR of the real-time stream and displays them in real time. is according to the moment appearing in the header of the blocks, on a screen of the terminal T1, during a step E38. From the moment when the instant H1 is reached by the current instant H, the blocks coming from the first enhancement stream CR1, that is to say the data blocks stored in the storage temporary memory MT of the downloaded stream , are inserted between the data blocks of the base stream CB according to the decode time of each of them (step E40). Thus, the blocks of the first enhancement stream CR1 are interleaved with the blocks of the base stream CB.

Then, the terminal T1 decodes the blocks of the basic flow CB and the inserted blocks of the portion of the enhancement stream CR1 downloaded and displays them in real time, ie according to the moment appearing in the header of the blocks, on a screen of the terminal T1, during a step E42 FIG. 2c illustrates the display of the base flow CB and a portion of the first CRl enhancement stream of audiovisual content Cl as a function of time. At first, only the basic CB flow blocks are decoded and the images displayed. From a given instant identified by the pointer P1, corresponding here to the third of the visualization from the beginning of the visualization of the content Cl, the downloaded blocks of the first enhancement stream CR1 begin to be inserted between the blocks of the stream. base and are provided to the decoding module interleaved with the blocks of the base stream. Thus, the images of the first enhancement stream are displayed in addition to the images of the base stream.

With reference to FIG. 5, a particular embodiment of the reception method will now be described.

The terminal T1 comprises a reception module REC able to receive the data blocks coming from the transmission line L1 and to transmit the received blocks to a processing module TRI of the terminal T1.

When receiving a data block, the processing module TRI determines whether the received block is a block that can be displayed in real time or whether the block received is a block of the stream received in download mode.

If the received block is a block of the real-time stream, that is to say a block of the basic stream CB in this embodiment, the processing module TRI saves this block in a temporary storage memory MR of the stream of time The temporary memory MR is a memory of the type "FIFO" (for "first input

- first output ").

If the block received is a block of the downloaded stream, that is to say a block of the first enhancement stream CR1, the processing module TRI saves this block in a temporary storage memory MT of the downloaded stream of the terminal T1. MT memory is a memory type "FIFO".

An ORD scheduling module of the terminal T1 then reads the headers of the received blocks stored in the real-time storage memory MR and in the storage memory MT of the downloaded stream and orders the blocks according to the indicated decoding instant. in their header. More precisely, the ORD scheduling module reads in the header of the first block stored in the real-time flow storage memory MR, the decoding time HR of this block.

Since the memory MR is a memory of the "FIFO" type, the block read in the memory MR is the block recorded before the other blocks present. The ORD scheduling module then reads in the header of the first block stored in the storage MT memory of the downloaded stream, the HT decoding instant of this block.

The memory MT being a memory type "FIFO", the block read in the memory MT is the block recorded before the other blocks present. The ORD scheduling module then compares the decoding time HR of the block of the real-time stream and the instant of decoding HT of the block of the downloaded stream.

If the decoding time HR of the block of the real-time stream is earlier than the instant of decoding HT of the block of the stream downloaded, the scheduling module ORD records the block read from the memory MR of storage of the real-time stream, in a decoding memory MD of the terminal Tl and erases this block from the storage memory MR of the real-time stream.

The ORD scheduling module then reads the next block in the MR memory and performs the comparison step again with the new HR value.

If the decoding time HR of the block of the real-time stream is later than the instant of decoding HT of the block of the downloaded stream, the scheduling module ORD records the corresponding block of the stream downloaded in the decoding memory MD and the erases the storage MT memory of the downloaded stream.

The ORD scheduling module then reads the next block of the downloaded stream and performs the comparison step again with a new value HT of the decoding time of the read block of the downloaded stream.

Thus, the blocks of the first enhancement stream CR1 being located after a determined pointer, the ORD scheduling module records in the decoding memory MD at first only blocks of the basic stream CB.

Then, from a given instant, it records blocks of the first enhancement stream CR1 between two consecutive blocks of the base stream CB. The given instant corresponds to the decoding instant of the first block received from the first enhancement stream CR1, that is to say the first block located after the determined pointer.

In parallel with the work done by the ORD scheduling module, as soon as a block is present in the decoding memory MD, a decoding module DEC of the terminal T1 reads this block, decodes it taking into account the decoding time. indicated in the header of the block and transmits it for display to an AFF display module of the terminal T1. Then, the decoding module DEC erases this block from the decoding memory MD. The decoding memory MD is a "FIFO" type memory. The block read in the decoding memory MD is always the block recorded before the other blocks present.

The display module AFF displays the images generated by the DEC decoding module. Thus, only images of the basic stream are displayed at first.

In a second step, from a given instant, one or more blocks of the enhancement stream are decoded between two blocks of the base stream.

The decoding and display of the enhancement stream, in addition to the decoding and display of the basic stream, improves from a given moment the quality of the display of the content and up to the end of the content.

With reference to FIGS. 6, 7a and 7b, a second embodiment of a transmission definition method, a transmission method and a method of reception of the audiovisual content C1 requested by a user of the terminal T1 according to FIG. The invention will now be described In this second embodiment, the rate DL3 of the line L1 is 700.

Kbits / s.

In this embodiment, the steps of the transmission configuration method are similar to the steps E2 to E1 described in the first embodiment. The first group of flows Gl determined in step E8 comprises the flow of CB base and the first CRl enhancement stream.

The second group of flows G2 determined during the step ElO comprises the second enhancement stream CR2.

The fraction of the second enhancement stream CR2 between the pointer P1 and the end of this stream, that is to say the end portion of the enhancement stream CR2, to be transmitted for download, determined during the step E 12 , corresponds to the second half of the CR2 flow. Thus, the pointer P1 is at half of the second enhancement file CR2.

During step E 14, the terminal T1 builds a streaming request RQR1 of the base stream CB and a streaming request RQR2 of the first enhancement stream CR1. The RQRl request contains the UBR URL and the RQR2 request contains the URl URL.

During the step E 16, the terminal T1 builds a request RQT1 for transmitting a portion of the CR2 enhancement stream in download mode. The RQT request contains the request UT2 URL of the second CR2 enhancement stream in download mode.

A second embodiment of a transmission method and a reception method consecutive to the method of configuration of a transmission which has just been described will now be described with reference to FIG. 6. During a step E50 , the terminal T1 transmits to the server S, a transmission request RQT1 of the second group of flows.

The server S receives the RQT1 during a step E52.

In a next step E54, the server S starts transmitting data packets of the second enhancement stream CR2 in download mode. The terminal T1 receives these data packets during a step E56 and stores them in a temporary storage memory of the downloaded stream of the terminal T1.

The terminal T1 sends back to the server S, during a step E58, an acknowledgment ACK of the received blocks.

In the following step E60, it reads the header of the received blocks and determines whether one of the blocks corresponds to the determined pointer P 1, that is to say if the quantity of information the second enhancement stream CR2 remaining to be transmitted corresponds to the quantity QI1 determined.

If it is not the case, the steps E54 to E60 are repeated. If this is the case, the terminal T1 transmits to the server S, during a step E62, the request requests RQR1 and RQR2 of the first group of streams in real time mode constructed during the step E14 of the configuration method of transmission.

The server S transmits, during a step E64, in response to the requests RQR1 and RQR2, on the one hand the base stream CB and on the other hand the first enhancement stream CR1, in real time mode and simultaneously (as represented in Figure 7a). It continues in parallel to transmit the second CR2 enhancement stream.

FIG. 7a illustrates the transmission of a first portion of the second raising flux CR2 and then the simultaneous transmission during the duration TD2 of displaying the content C2, the basic flow CB, the first raising flux CR1 and a second portion of the second CR2 enhancement stream. Thus, a first portion of the CR2 enhancement stream is transmitted in download mode by the server S to the terminal T1 before the start of the simultaneous transmission, on the one hand, of the base stream CB and the enhancement stream CR1 in real time mode , and, secondly, a second portion of the CR2 enhancement stream in download mode. The first part of the CR2 enhancement stream transmitted in download mode before the real-time transmission corresponds to a beginning portion of the content, while the second part of the CR2 enhancement stream transmitted in download mode concomitantly with the real-time transmission corresponds to a part of end of the content. The entire CR2 enhancement stream is thus transmitted. The terminal T1 receives, during a step E66, in parallel with the reception of the data blocks of the second enhancement stream CR2, data blocks of the first group of flows, that is to say the basic flow CB or the first enhancement stream CRl, which it stores in a temporary real-time storage memory of the terminal T1. During a step E68, the terminal T1 interlocks the blocks of the stream stored in the terminal. temporary storage of real-time flow storage and the blocks of the stream stored in the temporary memory of stream storage downloaded according to the block headers of these streams. In this embodiment, the given instant corresponds to the beginning of the visualization of the content. Step E68 is followed by a step E70 in which the interlaced stream is decoded and displayed.

FIG. 7b illustrates the display of the base stream CB, the first enhancement stream CR1 and the second enhancement stream CR2 of the audiovisual content C1 as a function of time. The CB basic flow blocks and the first CRl enhancement stream are decoded and the images displayed slightly delayed compared to the demand but, in return, all three streams are displayed at the beginning of the visualization, thus allowing to improve, from the beginning of the visualization and during all the duration of visualization, the quality of the display of the contents.

With reference to FIGS. 8 and 9, a third embodiment of a transmission configuration method, a transmission method and a method for receiving audiovisual content according to the invention will now be described.

In this embodiment, a user of the terminal T2 controls the transmission of the content C2.

As illustrated in FIG. 8a, the audiovisual content C2 is stored in the form of 3 files encoded in SVC: a file CB2 containing a base stream encoded at a bit rate DB2, for example 500 Kbps, a first file of enhancement R1 containing an enhancement stream coded at a rate DR4, for example 100 Kbits / s, and a second enhancement file R2 containing an enhancement stream coded at a rate DR5, for example 50 Kbits / s. With reference to FIG. 9, the terminal T2, during a first step E100, transmits to the server S via the transmission line L2 a request RQ2 for requesting the audiovisual content C2. The request RQ2 includes an identifier of the audiovisual content C2, for example the ISAN code of this content.

During a step E102, the server S receives the request RQ2. During a step E104, the server S sends, to the terminal T2, a response RR2 to The request RQ2. The response RR2 contains information relating to the files stored on the server S for the audiovisual content C2.

The information relating to the files stored for the audiovisual content C2 is for example a URL (for "Uniform Resource Locator") UB2 for requesting the base stream CB2 according to a first transmission mode, the DB2 encoding rate associated with the base file CB2, a URL Ul for requesting the first enhancement stream R1 according to a first transmission mode, an URL

U2 making it possible to request the second enhancement stream R2 according to a first mode of transmission as well as the coding rates DR4 and DR5 associated with the enhancement files R1 and R2.

The first mode of transmission is for example a real time mode, for example a "streaming RTP" mode.

The response RR2 is for example a conventional SDP type file.

The terminal T2 receives the response RR2 during a step E 106. During a step E108, the terminal T2 determines the bit rate DL2 of the transmission line L2.

In the embodiment described, the determined bit rate DL2 is 575 kbit / s

Then, during a step El 10, the terminal T2 builds and transmits two requests

RQR3 and RQR4 for streaming content C2. The number of requests depends on the rate L2 of the transmission line L2 and the flow of the content streams

C2. The number of requests is calculated so as to use the entire bandwidth of the transmission line L2.

The bit rate DL2 of the transmission line L2 is on the one hand greater than the coding bit rate DB2 of the base stream CB2 and, on the other hand, less than the sum of the coding bit rate DB2 of the base bit CB2 and the coding bit rate DR4. of the first enhancement stream R1.

The request RQR3 is a request for transmission of the basic flow CB 2 according to the first transmission mode. The request RQR4 is a transmission request of the first enhancement stream R1 according to the first transmission mode. As an alternative, the number of requests transmitted is greater than 2 while remaining within the limit of the number of C2 content streams.

As an alternative, the terminal T2 does not determine the bit rate DL2 of the line and transmits as many stream transmission requests according to the first transmission mode as the stream composing the content C2. The requests transmitted by the terminal T2 are received by the server S during a step El 12.

During an El step 14, the server S determines the rate DL2 of the transmission line L2. The method used to calculate the flow rate of the line is for example one of those described in the documents US2002044528, US2002165970 and EP 0622967.

As an alternative, the rate DL2 of the transmission line L2 is determined by the terminal T2 and transmitted in the request RQ2. Step El 14 is then a step of receiving information relating to the flow rate of line L2.

The coding bit rate DL2 of the transmission line L2 is for example 575 kbit / s.

In a next step El 16, the server S determines a first group G3 of streams able to be transmitted according to the first transmission mode. The bit rate DL2 of the transmission line L2 is on the one hand greater than the coding bit rate DB2 of the base stream CB2 and, on the other hand, less than the sum of the coding bit rate DB2 of the base bit CB2 and the coding bit rate DR4. of the first enhancement stream R1. Also, the first group of flows G3 consists of the basic flow CB2.

The first group G3 is thus determined as a function of the information relating to the bit rate of the line and as a function of flow rate information of the audiovisual content C2. During a step El 18, the server S determines a second group G4 of streams able to be transmitted in a second transmission mode. The second group of flows is for example constituted by the first enhancement stream R1.

The second group G4 is thus determined as a function of the information relating to the bit rate of the line and as a function of flow rate information of the streams of the audiovisual content C2. As an alternative, the second group of flows consists of the first enhancement stream R1 and the second enhancement stream R2.

The bandwidth or bit rate DD2 of the transmission line L2 remaining available during transmission of the first group of streams according to the first transmission mode is lower than the coding rate of the second group of streams G4.

In a subsequent step E 120, the server S determines a pointer P3 of the second stream group G4, that is to say the first enhancement file R1. For this purpose, the terminal T2 determines the quantity of information QI2 and the fraction F (R1) (or proportion) of the first enhancement stream R1 that can be transmitted during the transmission time of the basic stream CB2 according to the first transmission mode, that is to say during the time TD2 real-time broadcast of the audiovisual content C2. More precisely, the quantity of information QI2 is obtained by the formula: QI2 = TD2x (DL2-DB2) = TD2 x DD2, and the fraction F (R1) is DD2 / DR4.

In the embodiment described where the rate DL2 of the transmission line L2 is 575 kbit / s, the fraction F (R1) is ³ A of the enhancement flux R1.

In other words, a part corresponding to ³ A of the enhancement stream R1 can be transmitted as a download during the streaming transmission of the basic stream.

CB2.

The pointer P3 is such that the amount of information of the first enhancement file R1, between this pointer P3 and the end of the first enhancement file R2 corresponds to the determined fraction F (R1). The pointer P3 is located at (1- (DL2-DB2) / DR2) from the beginning of the file, in other words at ¹ A of the file from the beginning of this file. In the embodiment described, the pointer P3 is therefore at the first quarter of the first enhancement file R1. The value of the pointer P3 is adapted to be at the beginning of a data packet.

Then, in an El step 22, the server S calculates the time difference D between the transmission of two consecutive packets of the streams of the second group GA. The time difference between the sending of two consecutive data packets of a stream is predetermined according to the flow rate of the stream. In step E 122, this gap is recalculated according to the remaining line rate. The time difference D makes it possible to calculate the moment of transmission of the packets of the second group G4.

During an El 24 step, the server S controls the transmission of a first portion of the second stream group G4, that is to say the first enhancement stream R1. The first part starts at the beginning of the first enhancement stream R1 to the pointer P3.

This transmission is performed according to the first mode of transmission, that is to say in streaming mode with a block timing corresponding to the stream encoding rate. After a delay corresponding to the time TD2 (1- (DL2-DB2) / DR2), during which time the first part of the first enhancement stream R1 has been transmitted, the server S transmits, during a step E 126 , the first group of flows G3 according to the first mode of transmission.

During a step E 128, carried out simultaneously in step E 126, the server S transmits the second portion of the raising flux R1 corresponding to the portion of the flow R1 between the pointer P3 and the end of the stream R1.

This transmission is performed in a real-time mode, for example streaming with a different timing than the coding of the file. Thus, the data packets are transmitted with the time difference D determined during the step E 122. The real-time transmission with a modified timing represents a second mode of transmission.

Since the second enhancement stream R2 is not a selected stream of the second stream group G4, the server does not respond to a request request from the second enhancement stream R2 emitted by the terminal T2. FIG. 8b illustrates the transmission of the first part of the first enhancement stream R1 and then the simultaneous transmission, during the display time TD2 of the content C2, of the base stream CB2 and of the second part of the first enhancement stream R1.

During a step E 130, the terminal T2 receives the first part of the second group of flows G4 and stores the data blocks corresponding to this stream in a first temporary flow storage memory of the terminal T2.

The terminal T2 then receives blocks of data from the first group of streams G 3 (step E 132) which it stores in a second temporary storage buffer of the terminal T2. The terminal T2 receives, in parallel with the step E132, during a step E134, blocks of data of the first enhancement stream R1, corresponding to the second part of the second group of flows G4, which it stores in the first memory temporary storage of the flow of the terminal T2. The first temporary stream storage memory thus contains the first part and the second part, that is to say the whole of the second stream group G4.

In the following step E 136, the terminal T2 interleaves the data blocks of the first group of streams G3 and the second group of streams G4 by respecting the decoding time associated with each block. Thus, the blocks coming from the second group of streams G4, that is to say the blocks stored in the first temporary storage of flow, are inserted between the blocks coming from the first group of flows G3, that is to say say the blocks stored in the second temporary stream memory.

The interleaved blocks are then decoded, respecting the decoding time associated with each block, and displayed.

Thus in this embodiment, a first portion of the second group of streams G4 is received by the terminal T2 at first.

In a second step, the terminal receives in parallel data blocks of the first group of streams G3 and a second part of the second group of streams G4.

The real-time display is done with a slight delay, but from the beginning of the display, data blocks of the second group of G4 streams are used to improve the quality of the display.

Thus, the images displayed are of good quality throughout the duration of the display.

FIG. 8c illustrates the display of the basic stream CB2 and of the first enhancement stream R1 of the audiovisual content C2 as a function of time. The basic flow blocks CB2 and the first enhancement stream R1 are decoded and the images displayed with a slight delay in relation to the request but, in return, all the two streams are displayed from the beginning of the visualization, thus making it possible to improve, from the beginning of the visualization and during the entire viewing time, the quality of the content display. According to an embodiment chosen and represented in FIG. 10, a device implementing a transmission configuration method of audiovisual content C, coded in the form of a plurality of streams, according to the invention is for example a microcomputer 500 which comprises, in a known manner, in particular a processing unit 502 equipped with a microprocessor, a read-only memory of the ROM or EEPROM type 503, a random access memory of the RAM type 504 and a communication interface 505 with a transmission line LT.

The microcomputer 500 may comprise in a conventional and non-exhaustive manner the following elements: a keyboard, a screen, a microphone, a speaker, a disk drive, a storage medium ... This server 500 includes a module MT1 of treatment, a first module

Selection SEL1, a second selection module SEL2 and a pointer determination module DET.

The processing module MT1 is able to obtain information relating to the bit rate of the transmission line. The first selection module SEL1 is able to select, according to the information relating to the bit rate of the transmission line, a first group of streams among the plurality of streams to be transmitted according to a first transmission mode.

The second selection module SEL2 is able to select, according to the information relating to the bit rate of the transmission line, a second group of streams comprising at least one stream of the plurality of streams of audiovisual content C, said at least one flows not belonging to the first group.

The determination module DET is able to determine a pointer of the second group of flows, from which the transmission of the second group of flows is carried out according to a second mode of transmission and simultaneously with the transmission of the first group of flows. According to a particular embodiment in which the device 500 is further able to carry out the steps of a transmission method, the device 500 further comprises a module ME1 for transmitting / receiving data to or from the data line. LT transmission. In this embodiment:

the processing module MT1 is able to control the transmission of a definition file of the audiovisual content C requested by a terminal and the transmission / reception module ME1 is able to transmit this definition file;

the transmission / reception module ME1 is able to receive requests for transmission of flows;

the processing module MT1 is also able to control the transmission according to the first transmission mode, of the first group of flows;

the processing module MT1 is also able to control the transmission according to the second transmission mode and simultaneously with the transmission of the first group of flows, of a part of the second group of flows located after a determined pointer and corresponding to a portion of end of the content;

the transmission / reception module ME1 is able to transmit the streams according to the commands transmitted by the processing module MT1.

According to a particular embodiment, the processing module MT1 is further able to control the transmission of at least a part of the second group of flows located before the pointer, this transmission being performed before the transmission of the first group of flows.

The read-only memory 503 comprises registers storing a computer program PG1 comprising program instructions adapted to carry out the steps of a transmission configuration method according to the invention.

When powering up, the PGl program stored in the ROM

503 is transferred into the random access memory which will then contain executable code and registers for storing the variables necessary for the implementation of a step of obtaining information relating to the bit rate of the transmission line; first step of selection, based on the flow information of the transmission line, a first group of streams comprising at least one stream of the plurality of streams, a transmission step according to a first transmission mode, the first group of streams, a second selection stage, a function of information relating to the bit rate of the transmission line, of a second group of streams comprising at least one of the plurality of streams, said at least one stream not belonging to said first group; a step of determining a pointer of the second group of streams from which the transmission of the second group is carried out according to a second transmission mode and simultaneously with the transmission of the first group of flows. More generally, a means of storage, readable by a computer or by a microprocessor, integrated or not to the device, possibly removable, stores a program implementing the steps of a transmission configuration method of audiovisual content, according to the invention.

According to an embodiment chosen and represented in FIG. 11, a terminal implementing a method for receiving audiovisual content according to the invention is for example a microcomputer 600 which comprises, in a known manner, notably a processing unit. 602 equipped with a microprocessor, a read-only ROM or EEPROM ROM 603, a RAM type RAM 604, a screen 606 and a communication interface 605 with a transmission line LT. The terminal comprising a first reception module of at least a first stream relating to a content transmitted according to a first transmission mode, here real time and a second reception module adapted to receive a portion of at least a second stream relating to the content transmitted in a second transmission mode, here in download mode, and simultaneously to the first stream, said part of the second stream being relative to only a portion of the end of the content.

The microcomputer 600 may comprise in a conventional and non-exhaustive manner the following elements: a keyboard, a microphone, a speaker, a disk drive, a storage medium ...

The ROM 603 includes registers storing a computer program PG2 including program instructions adapted to perform the steps of the method of receiving an audiovisual content according to the invention.

When powering on, the program PG2 stored in the read-only memory 603 is transferred into the random access memory which will then contain executable code and registers for storing the variables necessary for the implementation of a transmission request step. flow, a first step of receiving a first group of streams transmitted in a first transmission mode, a decoding step and displaying the first group of streams, a second receiving step, in parallel to the first receiving step, a part of a second group of streams of the plurality of streams transmitted according to a second transmission mode, and located after a determined pointer of the second group of flows, a storage step of the part of the second stream received during the second reception stage, and from a given instant of the decoding of the first group of flows, a step of interleaving the stored stream and the first group of flows e t a step of decoding and displaying the interlaced stream. More generally, a means of storage, readable by a computer or by a microprocessor, integrated or not into the device, possibly removable, stores a program implementing a method of receiving an audiovisual content according to the invention.

Claims

A method for transmitting coded audiovisual content in the form of a plurality of data streams, from a server (S) to a terminal (T1, T2), comprising a step of transmission by the server of at least a first stream relating to the content according to a first transmission mode, characterized in that it further comprises a step of transmission by the server of a part of at least a second content-related stream according to a second mode of transmission , the two transmission steps being simultaneous and said part of the second stream transmitted simultaneously to the first stream being relative to only a part of the end of the content.

2. Transmission method according to claim 1, wherein there is provided a step of determination by the server of said at least one first stream to be transmitted according to the first mode of transmission and said at least one second stream a part of which is intended to be transmitted according to the second transmission mode, according to information relating to a bit rate of a transmission line to the terminal and information relating to the bit rates of the streams encoding the content.

The method according to claim 1, wherein another portion of said at least one second stream, relating to a start portion of the content, is transmitted before the start of the simultaneous transmission of the first stream according to the first mode of transmission and said part of the second stream according to the second transmission mode.

The method of claim 1, wherein the first transmission mode is a real time mode and the second transmission mode is a download mode.

5. A method of reception by a terminal of audiovisual content (C1, C2) coded in the form of a plurality of streams and transmitted by a server (S), comprising a step receiving at least a first stream relative to the transmitted content according to a first reception mode, characterized in that it further comprises a step of receiving a portion of at least a second stream relative to the transmitted content according to a second transmission mode, the two reception stages being simultaneous and said part of the second stream received simultaneously with the first stream being relative to only a part of the end of the content.

6. Reception method according to the preceding claim, wherein the terminal determines said at least one first stream to be transmitted according to the first transmission mode and said at least one second stream, part of which is intended to be transmitted according to the second transmission mode. , based on information relating to a bit rate of a transmission line to the terminal and information relating to the bit rates of the streams encoding the content.

7. The reception method according to claim 5, comprising

an interleaving step (E40) of the stored part of the second stream and the first stream, from a time corresponding to the beginning of said end portion of the content, and a decoding and display step (E42 ) of the interlaced stream.

The method according to claim 8, wherein another part of the second stream, relating to a start portion of the content, is received before the start of the simultaneous reception of the first stream according to the first transmission mode and said part of the second flow according to the second mode of transmission.

9. Server capable of transmitting audiovisual content (C1, C2), said content being coded according to a plurality of data streams, to a terminal (T1, T2), comprising first transmission means adapted to transmit at least a first stream content according to a first mode of transmission, characterized in that it further comprises second transmission means adapted to transmit a portion of at least a second stream relative to the content according to a second mode of transmission simultaneously with the transmission of the first stream according to the first transmission mode, said part of the second flow being relative to only a part of the end of the content.

Terminal for receiving audiovisual content (C1, C2) encoded in the form of a plurality of data streams, comprising first means for receiving at least a first stream relating to the content transmitted according to a first mode of transmission, characterized in that it further comprises second receiving means adapted to receive a portion of at least one second stream relative to the transmitted content according to a second transmission mode and simultaneously to the first stream, said part of the second stream being relative to only a part of end of the content.

11. System comprising a server according to claim 9 and at least one terminal according to claim 10.

A computer program product comprising instructions for carrying out the steps of a transmission method according to claim 1 when it is loaded and executed by a processor.

A computer program product comprising instructions for carrying out the steps of a reception method according to claim 7 when it is loaded and executed by a processor.