JP2007312122A - Network receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent influence on image reproduction due to jitter or clock asynchronization between a transmitting side and a receiving side in the case of receiving real-time data through a network. <P>SOLUTION: Real-time image data received through a communication network 3 are written in a buffer 8, read out from the buffer 8 and decoded by a decoder 9 and the decoded data are supplied to a display 10 to reproduce an image. When data volume to be stored in the buffer 8 is reduced due to jitter in the received image data or clock asynchronization (frequency deviation) between the transmitting side and the receiving side and an underflow inclination is generated, slow reproduction or a display image is freezed for a short period, the data volume to be stored in the buffer 8 is increased to solve the underflow inclination. When the data volume to be stored in the buffer 8 is increased and an overflow inclination is generated, quick reproduction or reading from the buffer 8 is skipped for a short period and the data volume to be stored in the buffer 8 is reduced to solve the overflow inclination. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a network receiver that receives video data distributed or broadcast in real time through a network such as an IP (Internet Protocol) broadcast and reproduces the video.

  2. Description of the Related Art Conventionally, there is a known system in which image data and audio data are transmitted from a transmission side communication terminal to a reception side communication terminal in real time (that is, unilaterally from the transmission side communication terminal) and received and viewed by the reception side communication terminal. It has been. In IP broadcasting, such image data and audio data (that is, real-time data) transmitted in real time are packetized and transmitted from the transmitting communication terminal to the receiving communication terminal in accordance with the IP standard. Is done.

  In this way, when communication is performed by packetizing such real time data between communication terminals, the transmission side communication terminal encodes the real time data, packetizes and transmits the data, and the reception side communication terminal receives the received real time data. It is written in the buffer in the order of received packets and temporarily stored, and is read and decoded in the order of writing. In this case, the decoding order of the packets must match the order of the packets at the time of reception.

  When communication is performed by packetizing real-time data between communication terminals, the transmitter communication terminal counts the clock for encoding real-time data in order to synchronize the clocks of the transmitter communication terminal and the receiver communication terminal. Then, the count value of the clock at the time of transmission is added as a time stamp for each packet, and the receiving side communication terminal again counts the clock for decoding, and the count value and the time stamp of the received packet Whether or not the clock of the receiving communication terminal is synchronized with the clock of the transmitting communication terminal from the change state of the difference value for each received packet (that is, whether the frequencies match) If it is not synchronized, a technique has been proposed that controls the clock frequency (for example, , See Patent Document 1).

  Also, in a system in which a video content file is downloaded from the video distribution server to the requested video receiving terminal in response to a request from the video receiving terminal, a time is set for each frame of video data of the video content file distributed by the video distribution server. A stamp is added, and the video receiving terminal receives the video data and temporarily stores it in the buffer. Based on the clock count value and this time stamp, each frame of video data from this buffer is written in the order of writing to the buffer. A technique for reading and decoding is disclosed (for example, see Patent Document 2).

  In the technique described in Patent Document 2, when video data is read from the buffer and decoded and reproduced by the video receiving terminal, the video receiving terminal where the communication failure has occurred can receive the video data. When the buffer is underflowed when the amount of video data stored in the buffer gradually decreases and falls below the set lower threshold (underflow threshold), the communication failure is recovered and video data download resumes. Until it is possible to stop reading video data from the buffer and interrupt video playback, and when the video data is read from the buffer and decoded by the video receiving terminal, video data is read from the buffer. Overflow condition that exceeds the upper limit threshold (threshold for overflow) set by increasing the amount of stored data gradually Then, the distribution from the video distribution server is stopped, the reading of the video data from the buffer and the video reproduction are continued, and when the accumulated data amount of the video data in the buffer falls below the overflow threshold, The download is resumed.

In the buffer used as described above, the video data is written from the head address, and when it is written to the last address, it returns to the head address and is written again from there. The same applies to reading. Thus, the buffer is functionally ring-shaped, and operates so that writing precedes and reading follows after that. Here, the amount of accumulated data in such a buffer is the amount of video data that has been written to the buffer but has not yet been read. Underflow of the buffer reduces the amount of accumulated data in the buffer. This is a state where the reading position (address) in the buffer overtakes the writing position. In addition, the buffer overflow is a state in which the amount of data stored in the buffer increases excessively and the write position in the buffer overtakes the read position.
JP 2000-332802 A JP 2003-289526 A

  By the way, when video data is communicated between communication terminals, if jitter occurs on the communication network, the transmission rate is equivalently changed. According to such jitter, the writing speed of the video data to the buffer for decoding at the receiving communication terminal changes, and the buffer underflows or overflows by adding this change in writing speed. To do. Further, if there is a deviation (synchronization deviation) in the clock frequency between the transmission side communication terminal and the reception side communication terminal, even if the synchronization deviation is minute, the video data is stored in the buffer of the reception side communication terminal. A difference between the writing speed and the reading speed occurs, and the difference in speed is accumulated, and the buffer underflows or overflows.

  Therefore, as in the technique described in Patent Document 1, when receiving real-time data, a buffer of the receiving communication terminal reads a packet with a time stamp that matches the count value of the clock by the counter. Therefore, if the buffer underflows due to jitter in the communication network or a clock synchronization error between the transmitting and receiving communication terminals, and the read position in the buffer overtakes the write position as described above, the clock count The write timing to the buffer of the packet whose time stamp matches the value is later than the timing of the count value of this clock, and the packet of the time stamp that matches the count value of the clock does not exist in the buffer. Unable to read packet from It becomes impossible to video playback me.

  On the other hand, when the buffer overflows, the write position in the buffer overtakes the read position, and from this overtake position, it is rewritten to a time stamp packet far from the clock count value. Thus, the time stamp packet that matches the count value of the clock is lost. As a result, packets cannot be read from the buffer, and video playback cannot be performed.

  In the technique described in Patent Document 2, when the amount of data stored in the buffer is equal to or less than a threshold for underflow control, reading of the video data from the buffer is prohibited and the video data is stored in the buffer. Therefore, underflow of the buffer can be avoided, and if the amount of data stored in the buffer exceeds the threshold for overflow control, downloading from the video distribution server is prohibited and video data is not stored in the buffer. Since data reading is continued, an overflow condition can be avoided.

  However, this is possible because the download of the video content file from the video distribution server is performed in response to a request from the video receiving terminal, and the real-time transmitted unilaterally as described in Patent Document 1 above. It cannot be applied to systems that handle video data and audio data.

  That is, in a real-time data communication system in which video data and audio data are transmitted unilaterally from a transmitting device such as an IP broadcast system, real-time data is transmitted regardless of the reception state on the receiving communication terminal side. Therefore, even if an overflow occurs in the decoding buffer of the receiving communication terminal due to the accumulation of jitter in the communication network and the minute frequency deviation of the clock on the transmitting side and the receiving side, the above-mentioned Patent Document 2 Like the described invention, the transmission of the real-time data in the transmission device cannot be interrupted, and reception of the real-time data must be interrupted in the receiving side communication terminal. As a result, the real-time data is received in this reception interruption period. Will be lost. When underflow occurs in the buffer, real-time data reception is not interrupted at the receiving communication terminal, so real-time data will not be lost, but video playback will be interrupted until underflow is canceled. During this time, the user cannot view the video, and the continuity of playback of video and audio of real-time data such as IP broadcast is impaired, giving the user an unnatural feeling.

  The object of the present invention is to solve such problems, and when receiving real-time data of video data or audio data through a communication network, jitter in the communication network or clock synchronization shift (frequency shift) with the clock on the transmission side It is an object of the present invention to provide a network receiver that can smoothly reproduce video and audio of received real-time data even if it occurs.

  In order to achieve the above object, the present invention provides a network receiver for receiving and reproducing video data distributed or broadcasted in real time through a network, a buffer for temporarily storing the received video data, and the buffer A decoder that decodes the video data read from the display, a display that is supplied with the video data decoded by the decoder and plays back video, and a control unit that controls the buffer and the decoder. To control the amount of stored data of the video data in the buffer during normal speed playback of the video data, and execute special playback for a short predetermined period according to the increase or decrease of the amount of stored data in the buffer, The special reproduction is restored to the normal speed reproduction with the elapse of the predetermined time.

  In addition, the present invention performs slow playback as the special playback when the amount of data stored in the buffer tends to be less than a set allowable lower limit threshold during normal speed playback, and performs normal speed playback. When the amount of data stored in the buffer tends to overflow more than a set allowable upper limit threshold value, fast-playing is executed as the special playback.

  In the present invention, the slow playback is about 0.8 times faster playback than the normal speed playback, and the fast-view playback is about 1.5 times faster playback than the normal speed playback. It is characterized by being.

  Further, the present invention is characterized in that the predetermined period is set by a timer.

  Further, the present invention is characterized in that the predetermined period ends when it is detected that the underflow tendency or the overflow has been eliminated by executing the special reproduction.

  In order to achieve the above object, the present invention provides a network receiver for receiving and reproducing video data distributed or broadcasted in real time through a network, a buffer for temporarily storing the received video data, and the buffer A decoder that decodes the video data read from the display, a display that is supplied with the video data decoded by the decoder and plays back video, and a control unit that controls the buffer and the decoder. To control the accumulated data amount of the video data in the buffer during normal speed reproduction by the video data, and (1) an allowable lower limit threshold in which the accumulated data amount of the buffer is set during normal speed reproduction. Stop reading the video data from the buffer for a short period of time when there is a trend of less thanday flow Then, special playback is performed to freeze the playback image on the display, and the normal speed playback is resumed after the predetermined period. (2) The amount of data stored in the buffer is set during normal speed playback. When the overflow tendency exceeds the allowable upper limit threshold, the video data reading in the buffer is skipped frame by frame as the special reproduction, and the normal speed reproduction is resumed at the end of the skip. It is characterized by this.

  Further, the present invention is characterized in that the predetermined period during which the buffer is in an underflow tendency and the reproduced image is frozen is set by a timer.

  Further, the present invention is characterized in that the switching from the normal speed reproduction to the special reproduction is a video scene switching unit based on the video data.

  Further, the present invention is characterized in that the switching from the normal speed reproduction to the special reproduction is performed as an audioless portion of the video based on the video data.

  Further, the present invention is characterized in that the predetermined period during which the special reproduction is performed is equal to or less than the period of the I picture in the GOP.

  According to the present invention, the jitter for real-time data in the communication network or the synchronization between the clocks of the transmission side and the reception side may cause the buffer for decoding the received real-time data to have an underflow tendency. Even if an overflow tendency occurs, special playback is performed only for a short time, so that the playback of the video can be continued and the underflow tendency or the overflow tendency can be eliminated with almost no disturbance or incongruity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a communication system using a first embodiment of a network receiver according to the present invention, where 1 is a network receiver of this embodiment, 2 is a data transmission device, 3 is a communication network, 4 Is an encoder, 5 is a sending unit, 6 is a clock generating unit, 7 is a receiving unit, 8 is a buffer, 9 is a decoder, 10 is a display, 11 is a control unit, and 12 is a clock generating unit.

  In the figure, in the data transmission device 2, real-time image data and audio data (hereinafter referred to as video data) from a signal source (not shown) are supplied to the encoder 4, and a clock (from the transmission side) is transmitted from the clock generator 6. Clock) φ1 is used for encoding. As such an encoding method, for example, a compression coding method based on MPEG (Moving Picture Experts Group phase) 2 or 4 standard is used. The encoded video data is supplied to the sending unit 5, packetized according to, for example, IP (Internet Protocol), sent to the communication network 3 such as the Internet, and distributed or broadcast to the network receiver 1. Such transmission of the video data is performed under a transmission unilaterally defined by the data transmission device 2. Here, only one network receiver 1 is shown as a representative.

  In the network receiver 1, video data based on IP sent through the communication network 3 is received by the receiving unit 7 (here, the video data is separated into image data and audio data, but here, collectively Explained as video data). The video data is sequentially stored in the buffer 8 under the control of the control unit 11, sequentially read out, and supplied to the decoder 9. In the decoder 9, the video data packets sequentially supplied from the buffer 8 are decoded using the clock φ 2 from the clock generator 12 under the control of the controller 11. The decoded video data is supplied to the display 10 and displayed as, for example, an IP broadcast video.

  In the buffer 8, the received video data is written at the timing of the clock φ, and is read out at the timing of the clock (reception side clock) φ 2 from the clock generation unit 12, but is being transmitted in the communication network 3. When jitter (frequency fluctuation) occurs in the video data (in this case, the clock φ of the received video data fluctuates), or the clock φ1 on the transmission side and the clock φ2 on the reception side If there is a frequency shift (clock synchronization shift), even if the clock synchronization shift is very small, a difference occurs between the video data writing rate and the reading rate in the buffer 8, By adding the difference, underflow or overflow occurs in the buffer 8.

  FIG. 2A shows a state in which the buffer 8 tends to underflow. This is because the accumulated data amount V is equal to or less than the allowable lower limit threshold TH1 of the accumulated data amount set in the buffer 8. This is the state when Here, the buffer 8 is functionally ring-shaped as described above, and the accumulated data amount V is the amount of video data that has not been read out in the buffer 8. Is.

  As described above, the received video data includes jitter, or there is a synchronization shift between the clock φ1 on the transmission side and the clock φ2 on the reception side, so that the writing rate of the video data to the buffer 8 is increased. When the reading rate from the buffer 8 is smaller, the accumulated data amount V in the buffer 8 decreases with time. The control unit 11 constantly monitors the accumulated data amount V in the buffer 8, and as shown in FIG. 2A, when the accumulated data amount V becomes equal to or less than the allowable lower limit threshold TH1, the control unit 11 Is determined to have an underflow tendency, and a control process to be described later for canceling the underflow tendency is performed.

  FIG. 2B shows a state in which the buffer 8 tends to overflow. This is because the accumulated data amount V is equal to or less than the allowable upper limit threshold TH2 of the accumulated data amount set in the buffer 8. It means the state when it becomes.

  As described above, the received video data includes jitter, or there is a synchronization shift between the clock φ1 on the transmission side and the clock φ2 on the reception side, so that the writing rate of the video data to the buffer 8 is increased. When the reading rate from the buffer 8 is larger, the accumulated data amount V in the buffer 8 increases with time, and as shown in FIG. 2B, when this accumulated data amount V becomes equal to or greater than the allowable upper limit threshold TH2, The control unit 11 determines that the buffer 8 has a tendency to overflow, and performs control processing to be described later for canceling this overflow tendency.

  FIG. 3 is a flowchart showing a control routine of the control unit 11 in the first embodiment of the network receiver 1 in FIG.

  In the figure, when the video data is read from the buffer 8, decoded by the decoder 9, and normal speed video reproduction is performed on the display 10 ("Y" in step S101), the amount of data stored in the buffer 8 It is determined whether or not V is smaller than the allowable lower limit threshold TH1 (step S102). As shown in FIG. 2 (a), when the number is reduced (“Y” in step S102), it is assumed that the buffer 8 tends to underflow. The reading in the buffer 8 and the decoder 9 are controlled so that the reproduction is performed for a short time (step S103). The execution time of this slow playback is measured by a timer (not shown). When this slow playback is started, this timer is started (step S106), and when a short predetermined set time elapses, there is an interrupt from the timer. (Step S107), the reading of the buffer 8 and the decoder 9 are controlled to return to normal-speed video reproduction (Step S108).

  In the case of normal speed video reproduction, the video data of each frame is sequentially read from the buffer 8 at a prescribed frame period (for example, 1/30 second), and the video of each frame is decoded at this period and sequentially displayed on the display 10. In the case of slow reproduction, the clock φ2 from the clock generator 12 is made slower than the normal speed reproduction, thereby reducing the number of frames for reading and decoding video data from the buffer 8. For example, in the case of the above-mentioned 0.8 × slow playback, 8 frames are decoded in a period corresponding to 10 frames. However, since the image is displayed ten times, the same frame is repeatedly displayed twice.

  In this manner, during the slow reproduction period, the received video data is written to the buffer 8 as usual, while the video data read is less than usual.

  FIG. 4A is a diagram illustrating a change in the amount of accumulated data V in the buffer 8 when an underflow tendency occurs.

In FIG. 4 (a), when it is detected that the accumulated data amount V of the normal speed reproducing buffer 8 is V1 smaller than the allowable lower limit threshold TH1 and tends to underflow, slow reproduction is performed. At this time, however, the reading of the video data from the buffer 8 is performed with a decrease, but the amount of video data read from the buffer 8 during this slow playback period (the period defined by the timer) is reduced. Assuming ΔVr, the read data amount V2 stored in the buffer 8 becomes V1−ΔVr. Since the video data is continuously written to the buffer 8 during the slow reproduction period, if the write amount is ΔVw, the accumulated data amount V of the buffer 8 immediately after the end of the slow reproduction period is:
V = V2 + ΔVw = V1 + (ΔVw−ΔVr)
It becomes. Here, in the slow reproduction period, the amount of video data read from the buffer 8 decreases, so ΔVw> ΔVr,
Accumulated data amount V at the end of slow playback> Accumulated data amount V1 at the start of slow playback
It becomes. As a result, the accumulated data amount V at the start of the slow playback end exceeds the allowable lower limit threshold TH1, and the underflow tendency of the buffer 8 can be eliminated.

  In this way, even if there is an underflow trend, the video will be played back without interruption, and by making the slow playback period as short as possible, the slow playback will be inconspicuous and the underflow trend will be reduced. It can be solved.

  In FIG. 3, during normal speed video reproduction (“Y” in step S <b> 101), as shown in FIG. When the number of overflows tends to increase (step S102 is “N” and step S104 is “Y”), for example, the buffer 8 is set so that 1.5 times normal speed playback of normal speed video playback is performed for a short time. Reading and the decoder 9 are controlled (step S105). The execution time of this quick-view playback is also measured by a timer (not shown), and at the same time as the start of this quick-view playback, this timer is started (step S106). Then, the reading in the buffer 8 and the decoder 9 are controlled to return to normal speed video reproduction (step S108).

  In this quick-view reproduction, the number of frames to be read and decoded from the buffer 8 is increased by making the clock φ2 faster than the normal-speed reproduction. In the case of the 1.5 × speed fast-view playback, video data for 3 frames is read from the buffer 8 and decoded in a period corresponding to 2 frames. However, since the image is displayed only twice, one frame is skipped and this is repeated. In this way, the readout of video data from the buffer 8 increases during normal speed playback.

  FIG. 4B is a diagram showing a change in the accumulated data amount V in the buffer 8 when the tendency to overflow occurs.

In FIG. 4B, when the stored data amount V in the buffer 8 becomes V1 larger than the allowable upper limit threshold TH2 and tends to overflow, fast-playing is performed as described above. Since the video data is read from the video data, the amount of video data read from the buffer 8 during this quick-playback period (the period specified by the timer) is ΔVr. Although V2 = V1−ΔVr, video data is continuously written to the buffer 8 during the quick-playback period. Therefore, if the write amount is ΔVw, the buffer 8 is stored immediately after the quick-playback period ends. The amount of data V is
V = V2 + ΔVw = V1− (ΔVr−ΔVw)
It becomes. Here, in the quick-view reproduction period, since there is more reading in the buffer 8 than in the writing of the video data, ΔVw <ΔVr,
Accumulated data amount V at the end of fast-playing reproduction <accumulated data amount V1 at the start of fast-playing reproduction
It becomes. As a result, the accumulated data amount V at the end of the quick-view reproduction becomes smaller than the allowable upper limit threshold TH2, and the tendency of the buffer 8 to overflow can be eliminated.

  In this way, even if the buffer 8 tends to overflow, the video playback is performed without interruption, and the fast-play playback period is made as short as possible to make the fast-play playback inconspicuous and to cause an overflow tendency. Can be resolved.

  In FIG. 3, during normal-speed video reproduction (“Y” in step S101), the accumulated data amount V in the buffer 8 is equal to or greater than the allowable lower limit threshold TH1 (“N” in step S102), and is equal to or greater than the allowable upper limit threshold TH2. (N in step S104), the normal-speed video reproduction continues as it is (that is, a series of operations in steps S101, 102, and 104 are repeated). Also, during special playback such as slow playback or fast-view playback ("N" in step S101), the special playback is continued from this control routine until the user gives an instruction to end the playback, If there is an instruction to stop normal speed reproduction from the user ("N" in step S101), the control routine is departed.

  As described above, in the first embodiment, the amount of data stored in the buffer 8 recovers from an underflow tendency or an overflow tendency during a period during which special playback such as slow playback or fast-view playback is performed.

  As a result, even if fluctuations in the amount of received data due to jitter of video data received through the communication network 3 or clock synchronization deviation on the transmission / reception side occur, and therefore fluctuations in the writing rate of the video data in the buffer 8 occur. Smooth video reproduction can be realized without incurring the failure of the buffer 8 due to overflow or underflow (the displayed video becomes defective in decoding or the video is interrupted).

  It should be noted that the ratio of the playback speed to the normal speed playback of slow playback or fast-view playback is shown as an example, and is not limited to this as long as the decoder 9 used can operate.

  FIG. 5 is a flowchart showing a control routine of the control unit in the second embodiment of the network receiver according to the present invention.

  The configuration of the second embodiment is the same as that shown in FIG. This control routine shown in FIG. 5 is different from the special reproduction executed when the buffer 8 tends to underflow or overflow, and is otherwise the same as the first control routine shown in FIG. It is. That is, in FIG. 5, step S103 in FIG. 3 is set as step S203, and step S105 in FIG. 3 is set as step S205. The other steps are the same as those in FIG. Steps have the same step numbers as in FIG. Below, the description which overlaps with FIG. 3 is abbreviate | omitted.

  In FIG. 5, the video data is read out from the buffer 8, decoded by the decoder 9, and normal-speed video reproduction is performed on the display 10 ("Y" in step S101). As shown in FIG. 2A, when the data amount V is smaller than the allowable lower limit threshold TH1 (“Y” in step S102), it is determined that the tendency of underflow has occurred, and the display 10 The display image is frozen (that is, the still image is reproduced), the reading of the video data from the buffer 8 is stopped, and the decoding by the decoder 9 is stopped (step S203). This freeze state is also performed for a predetermined set time determined by the timer (steps S106 to S107), and when the predetermined set time elapses, normal video playback is resumed (step S108).

  FIG. 6A is a diagram showing a change in the amount of accumulated data V in the buffer 8 when an underflow tendency occurs in the second embodiment.

In FIG. 6A, when the accumulated data amount V of the buffer 8 becomes V1 smaller than the allowable lower limit threshold TH1 and tends to underflow, the reproduced image on the display 10 is frozen. However, when the reproduced image is frozen, the video data is not read in the buffer 8, but the video data is still written in the buffer 8. Then, when a predetermined set time determined by the timer elapses, the freeze state returns to the normal speed video reproduction state. If the data amount of the video data written in the buffer 8 during the predetermined set time is ΔVw, The amount of data V stored in the buffer 8 at this time is
V = V1 + ΔVw
Therefore, V> V1. As a result, the accumulated data amount V can exceed the allowable lower limit threshold TH1.

  In this way, even if the buffer 8 tends to underflow, the video is reproduced without interruption, and the freeze reproduction is made inconspicuous by making the freeze reproduction period as short as possible. The tendency of the flow can be eliminated.

  In FIG. 5, normal speed video reproduction is performed on the display 10 (“Y” in step S101), and the amount of data V stored in the buffer 8 at this time is as shown in FIG. If it exceeds the allowable upper limit threshold TH2 ("N" in step S102 and "Y" in step S104), it is determined that the buffer 8 tends to overflow, and a plurality of read positions in the buffer 8 are set. Skip frames and skip (step S205). When reading of the video data is started after skipping a plurality of frames in the buffer 8, the normal video playback is resumed from the frame of the video data from which the reading has been started (step S108). The skipped frames are not read but are treated as being read.

  FIG. 6B is a diagram showing a change in the amount of accumulated data V in the buffer 8 when the tendency of overflow occurs.

  In FIG. 6B, when the accumulated data amount V in the buffer 8 becomes V1 larger than the allowable upper limit threshold TH2 and tends to overflow, the display image on the display 10 is set in a frozen state as described above. In the buffer 8, the reading position is skipped for a plurality of frames, and the plurality of frames are discarded without being read (that is, already read).

Here, if the data amount of a plurality of skipped frames is ΔVs, the accumulated data amount V2 in the buffer 8 becomes V1−ΔVs due to this skip, but video data is continuously written to the buffer 8 during this skip. Therefore, if the amount of write data is ΔVw, the amount of data V stored in the buffer 8 when the skip is finished and the normal speed video reproduction is resumed is
V = V2 + ΔVw = V2− (ΔVs−ΔVw)
It becomes. Here, since the skip is performed in a short time, the data amount ΔVs lost by the skip is larger than the video data write data amount ΔVw during that time, so ΔVw <ΔVs,
Accumulated data amount at the end of skip V <Accumulated data amount at the start of skip V1
It becomes. As a result, the accumulated data amount V at the end of skip becomes smaller than the allowable upper limit threshold TH2, and the overflow tendency of the buffer 8 can be eliminated.

  In this way, even if the buffer 8 tends to overflow, the video reproduction is performed without interruption, and the skip period is shortened as much as possible to make the display image freeze inconspicuous. Can be eliminated.

  In the second embodiment, when the buffer 8 tends to underflow, reading of the video data from the buffer 8 is stopped, and when the buffer 8 tends to overflow, the reading position in the buffer 8 is set for a plurality of frames. Since it is skipped, when it tends to underflow or overflow, the tendency can be resolved earlier than in the first embodiment, and failure due to overflow or underflow may occur. Video (image / sound) can be reproduced smoothly.

  In each of the above embodiments, the special reproduction that is performed when the buffer 8 tends to overflow or underflow may be started at a scene change or silent portion. According to this, it is possible to make it difficult for the viewer to notice that special playback has been performed, and to reduce the sense of discomfort.

  In each of the above embodiments, the timer is used to perform the special reproduction for a short time. Instead, the accumulated data amount in the buffer 8 is a value in which the overflow tendency or the underflow tendency is eliminated. It is also possible to switch from special playback to normal speed playback by detecting that Although the special reproduction time varies depending on the allowable lower and upper thresholds of the buffer 8 and how to select the timer, the period of the I picture (intra-frame coding screen) (approximately 1 / frame) for each GOP (Group Of Picture) of the received video data. 2 seconds) or less, preferably about one frame period (1/30 second) (about one frame period (1/30 second)). The display 10 displays an image of one frame during this period. ), Which is desirable to prevent viewers from recognizing and feeling uncomfortable.

  Further, in each of the above embodiments, the video data transmission device 2 in FIG. 1 is shown as an example in which a real-time encoder is used as the encoder 4 therein and the data is transmitted as it is after encoding. However, the encoded data is temporarily stored. Thus, it is obvious that the same effect can be obtained as a server device that prepares and transmits and distributes the data.

It is a block block diagram which shows 1st Embodiment of the network receiver by this invention. It is a figure which shows the underflow tendency and the overflow tendency to the buffer in FIG. It is a flowchart which shows the control routine of 1st Embodiment of the network receiver by this invention. It is a figure which shows the cancellation | release operation | movement of the buffer underflow tendency and the overflow tendency by the control routine shown in FIG. It is a flowchart which shows the control routine in 2nd Embodiment of the network receiver by this invention. It is a figure which shows the cancellation | release operation | movement of the buffer underflow tendency and the overflow tendency by the control routine shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Network receiver 2 Image | video data transmission device 3 Communication network 4 Encoder 5 Transmission part 6 Clock generation part 7 Reception part 8 Buffer 9 Decoder 10 Display 11 Control part 12 Clock generation part V Accumulated data amount

Claims (10)

In a network receiver that receives and plays back video data distributed or broadcast in real time over a network,
A buffer for temporarily storing the received video data;
A decoder for decoding the video data read from the buffer;
A display that receives the video data decoded by the decoder and reproduces the video;
A control unit for controlling the buffer and the decoder,
Under the control of the control unit, the amount of stored data of the video data in the buffer during normal speed playback of the video data is managed, and special playback is performed for a short predetermined period according to the increase or decrease of the stored data amount of the buffer. A network receiver that executes and returns from the special reproduction to the normal reproduction with the lapse of the predetermined time. In claim 1,
When the amount of data stored in the buffer tends to be less than the set allowable lower limit threshold during normal speed playback, slow playback is executed as the special playback,
A network receiver, wherein fast-play playback is executed as the special playback when the amount of data stored in the buffer tends to overflow more than a set allowable upper limit threshold during normal-speed playback. In claim 2,
The slow playback is about 0.8 times faster playback than the normal speed playback,
The network receiver according to claim 1, wherein the fast-view playback is about 1.5 times faster playback than the normal speed playback. In any one of Claims 1-3,
The network receiver according to claim 1, wherein the predetermined period is set by a timer. In claim 2 or 3,
The network receiver according to claim 1, wherein the predetermined period is ended by detecting that the underflow tendency or the overflow tendency has been eliminated by executing the special reproduction. In a network receiver that receives and plays back video data distributed or broadcast in real time over a network,
A buffer for temporarily storing the received video data;
A decoder for decoding the video data read from the buffer;
A display that receives the video data decoded by the decoder and reproduces the video;
A control unit for controlling the buffer and the decoder,
Under control of the control unit, the amount of data stored in the buffer in the buffer is managed during normal speed playback using the video data.
(1) When the amount of accumulated data in the buffer tends to be less than the set allowable lower limit threshold during normal speed reproduction, the reading of the video data from the buffer is stopped for a short predetermined period, Performs special playback to freeze the playback image on the display, and after the predetermined period, returns to the normal speed playback,
(2) During normal speed playback, when the amount of data stored in the buffer tends to overflow more than a set allowable upper limit threshold, video data reading in the buffer is skipped frame by frame as the special playback. And a network receiver which returns to the normal speed reproduction upon completion of the skip. In claim 6,
The network receiver according to claim 1, wherein the predetermined period during which the buffer is in an underflow tendency and the reproduced image is frozen is set by a timer. In any one of Claims 1-7,
The network receiver according to claim 1, wherein switching from the normal speed reproduction to the special reproduction is performed by a video scene switching unit based on the video data. In any one of Claims 1-7,
The network receiver according to claim 1, wherein switching from the normal speed reproduction to the special reproduction is performed in a soundless portion of the video based on the video data. In any one of Claims 1-9,
The network receiver according to claim 1, wherein the predetermined period during which the special reproduction is performed is equal to or less than a period of an I picture in a GOP.

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