KR20130017404A

KR20130017404A - Apparatus and method for reducing zapping delay using hybrid multimedia service

Info

Publication number: KR20130017404A
Application number: KR1020110079798A
Authority: KR
Inventors: 서덕영; 고정곤; 박광훈; 김규헌
Original assignee: 경희대학교 산학협력단
Priority date: 2011-08-10
Filing date: 2011-08-10
Publication date: 2013-02-20

Abstract

The present invention relates to a method of serving multimedia content in an Open IP network, and aims to increase image quality of a mobile terminal while reducing channeling delay through multimedia content having hierarchical quality. The present invention discloses a method of reducing a channel change delay time generated during a channel change in an Open IP multicast broadcast service through a unicast (1: 1 time sharing service) preview channel.

Description

Method and apparatus for reducing channel change delay using hybrid multimedia service {APPARATUS AND METHOD FOR REDUCING ZAPPING DELAY USING HYBRID MULTIMEDIA SERVICE}

The present invention relates to a method of reducing channel changing delay in a multimedia service.

Multimedia services are interactive services such as video telephony, streaming services such as Video On Demand (VOD) services, and multicast and broadcast services. Meanwhile, the real-time multimedia service may be divided into an interactive service, an interactive service, and a streaming service according to the type of service. In addition, the real-time multimedia service can be divided into unicast, multicast, and broadcast according to the number of users participating.

Among them, with the development of the Internet and the spread of PCs (personal computers), more and more users are watching broadcasts using PCs rather than TVs. One example is the increasing number of users who watch baseball games using the streaming system of the portal site. In case of broadcasting by multicast in Open IP network, buffering occurs for about 4-5 seconds considering channel quality is variable when changing channel, which causes delay to service of changed channel. This is called a channel changing delay, which may be inconvenient for a user who receives a service. The method to reduce this has been steadily studied.

Video coding and SVC

Scalable Video Coding (SVC) is an addition to the H.264 / MPEG-4 AVC standardized by the Joint Video Team (JVT) of ITU-T and ISO / IEC JTC 1 to layer the existing H.264 / MPEG-4 AVC. Is a standard for how to encode and decode a stream. Initiated by the continual evolution of receiving devices and the increasing usage of the transmission system, which is characterized by a variety of data reception qualities, svc is immediately adaptable to application requirements such as processing power, display capabilities, and various network transmission states of target devices.

Video coding is used to deliver a wide variety of applications over wired and wireless networks, from multimedia messaging, video telephony and video conferencing to high-end TV broadcasts. In particular, when transmitting data over a wireless network, there are various transmission states that can be handled using the layering feature of svc in the system. In addition, the same multimedia content is delivered to various receiving devices having different display and processing capabilities. SVC thus allows everything to cover a variety of environments and allows for flexible application.

The existing H.264 / MPEG-4 AVC has a hierarchical reference structure between pictures. The I frame can be independently decoded by configuring I, P, and B frames, and the P frame is an I frame or another P frame, and the B frame is a structure for decoding with reference to an I frame, a P frame, or another B frame. SVC extends this structure to create temporal, spatial and quality layered streams, making it compatible with existing AVCs, and creating streams that can adapt to a variety of applications and network conditions.

1 is a diagram illustrating an example of scalable video coding. This hierarchical reference structure shows high compression efficiency even in H.264 / MPEG-4 AVC and is effective in terms of SVC functionality. However, this structure has a disadvantage that the upper layer can be decoded only when the lower layer exists. In SVC, the lower layer tends to have less information while the upper layer tends to have more information. Since the lower layer has a greater impact on the image quality than the upper layer, the UEP (un-equal protection) may be applied to the layered bit stream according to its importance.

How to reduce conventional channel change delay

2 illustrates a conventional method for reducing zapping delay using SVC. Referring to FIG. 2, it can be seen that the period of the intra frame of the upper layer is 9 and the period of the intra frame of the lower layer is 3. By changing the encoding units of the upper layer and the lower layer, it can be seen that the position of the intra frame of the upper layer and the position of the intra frame of the lower layer are different. When the channel is changed, when the lower layer is decoded and outputted until the intra frame of the upper layer is received, the zapping delay felt by the user is shortened, thereby improving QoE.

In addition, there is a method of reducing the channel change delay in the prior art by providing a multicast service to the preview channel that transmits the multimedia with a lower bit rate than the service video to all users. Minimum quality can be guaranteed until buffering is complete.

The present invention provides a method and apparatus for servicing a unicast preview channel in order to reduce a channel change delay occurring when providing an Open IP multimedia service.

The present invention relates to a method of improving image quality and reducing delay time by using a preview channel using unicast in order to reduce a zapping delay in a multimedia service using Open IP multicast.

The present invention provides a preview service for only one user by serving as a unicast for the user only if the user wants to change the channel, rather than the preview channel serviced by the existing multicast. This ensures a progressively higher quality transmission during the buffering time, ensuring not only QoS but also QoE.

According to the present invention, a channel change delay can be reduced through a unicast (1: 1 time sharing service) preview channel in an Open IP multicast broadcast service.

1 is an example of scalable video coding
2 is a conventional method for reducing zapping delay using SVC
3 is a network diagram of the proposed method
4 is a method for reducing a channel change delay through a preview service
5 is a zapping processing procedure when using the preview service
6 illustrates a zapping process when the preview service is not used
7 shows the RD curve according to each case
8 provides a broadcast service over time
9 is a change in image quality over time

Like the Open IP streaming service, multiple multimedia channels exist, and the original video may lose or error. The technique used to restore this is channel coding, and one of the methods is to restore the data by attaching the FEC to the data. In addition, a delay that occurs when a user changes a channel from time to time is called a zapping delay, which inconveniences the user. In streaming services, this delay is known to be 4-5 seconds.

The present invention proposes a method of maximizing image quality of a preview channel by maximizing a user's QoE by transmitting the preview channel in a unicast manner for only one user.

The existing broadcast is served by a broadcast network, and the preview channel is served by a broadband network. The preview channel is serviced 1: 1 in broadcast, and the quality of this channel is very low compared to the broadcasted multimedia and therefore the bit rate is very low.

Broadcasts broadcast over the Internet are buffered for a few seconds for dejittering, so it takes time for them to be fully buffered even during zapping. In this patent, when the channel change request, the stream of the preview channel is transmitted to minimize the buffering time.

3 is a diagram showing the contents of the proposed method. When the user requests a channel change, this information is sent to the server providing the preview service, and upon receiving this signal, the server transmits the preview data for the changed 1: 1 channel to the requesting user. It transmits until buffering of desired broadcast is completed through broadcast network. The preview channel is sent in 1: 1 so you can send the necessary data bursty

When the user requests a channel change, this information is delivered to the server providing the preview service, and upon receiving this signal, the server transmits the preview data for the changed 1: 1 channel to the requesting user. Transmit until buffering for the desired broadcast is completed through the broadcast network.

How to reduce channel change delays with preview service

4 is a diagram illustrating a method for reducing a channel change delay through a preview service. This server provides multimedia service through broadcasting to various users as follows. While User 1 requests a channel change at tc time and is buffered to receive services from other channels, the Preview Server will provide User 1 with lower quality multimedia than this server, and User 1 will provide this service during the buffering time. The minimum quality is guaranteed during the channel change delay time.

Users connected to the preview server and not Between users zapping Differences in Processing Procedures

Referring to FIG. 5, it is time tc requests a change from broadcast M to broadcast N. FIG. In order to minimize the buffering time, the multimedia of the preview channel is provided with a very low quality video compared to the present channel. Lower quality means lower bit rate, and the lower bit rate reduces the buffering time. tpb is a time for which the buffering of the preview image is completed and provided to the user. Between tc and tpb, the user passes the channel change information of the user to the server of the preview channel. From the buffered tpb, the user can be provided with the preview service.

This channel should be provided with the best multimedia service. As a result, the bit rate is increased and the buffering time is longer than that of the preview channel. Buffering is performed in this channel between tpb and tb, and the expected time (tb) at which buffering is completed is transmitted to the preview channel. From tb, the user is provided with the service of this channel, and the preview channel waits for another user who requests a channel change.

6 is a diagram illustrating a zapping processing procedure of a user who does not use the preview channel. tc is the time when the user requests to change the channel, and tb is the time when the buffering is finished and start providing the service of the broadcast N to the user. Compared with the picture above, since the preview channel is not used, the service cannot be provided until buffering for the service of broadcast N is simply completed in this channel. During the buffering time, the user waits while watching the black screen or the last screen of broadcast M.

The quality of the broadcast vs . Preview broadcast quality (comparative analysis in three cases)

In terms of bit rate and PSNR, the three cases of Table 1 are compared in the present and preview broadcasting services.

According to the above case, each R-D curve is shown as a graph in FIG. 7.

In each case, the bit rate of the preview image is 5-20% of the present image, and the PSNR is about 4-8 dB. The preview video is a video that passes by instantaneously. The quality does not need to be high as long as it is possible to check which multimedia is currently being broadcast. Therefore, if you use 270 X 120, which is the preview image of case 3, you can use the preview service with only 5% of the delay time of the video. If you calculate the delay of the video as 3 seconds, you want to change it in 0.15 seconds. It is possible to check what multimedia services are provided in the channel, which can satisfy the user's satisfaction.

Content of the information to pass to the preview server

In order for the user to request a channel change, information for this will need to be delivered to the server providing the preview service. This may include the following.

Signal for channel change: channel_change_signal;

Channel number of the channel the user wants to watch: channel_change_num (int);

Multimedia broadcasting on the channel: main_channel_media;

Basically, you will need the virtual channel number of the channel you want to see. This will allow the preview server to begin preparing to transfer the data for that channel. In addition, it is necessary to know what multimedia is currently broadcasting in the channel, and knowing the buffering time for the service through the bit rate of the multimedia, it is possible to predict from which point in time to serve the video. In addition, the buffering time required to service the channel information in the present channel can be known to predict the time point from the preview channel to the present channel.

From the user's point of view, the service can be provided by the following procedure.

send channel_change_signal;

send channel_change_num;

start buffering main_channel_media;

if user finish main_channel_media buffering

start service main_channel_media;

else

start service pre_channel_media;

How to calculate when the preview service is provided

Although the preview service is smaller than the video, the buffering time is present. If the user requests the channel change time to be tc and the buffering time taken for the service in the preview channel is tpb, the preview service will be provided at tc + tpb. In other words, the preview channel may be serviced by starting buffering from the image of the time broadcasted to tc + tpb.

8 is a diagram illustrating the provision of a broadcast service over time. Since the preview service knows what data is broadcasted in broadcast N at the time of tc + tpb, the preview broadcast can determine the service time. Since tnb knows the multimedia broadcast on channel N, the preview broadcast N contains multimedia data up to tb. After all of the multimedia data is transmitted to the user, the broadcasting of the channel N can be immediately watched.

Preview service in terms of quality

In the preview channel, the buffer will continue to receive data during the service period. And it is gradually larger than the minimum bit rate for the video service. Therefore, when buffering is completed initially, the video can only broadcast the minimum quality for broadcasting. However, since the size of the data that can be used gradually increases, the video can be serviced with a better image than the minimum quality. 9 is a graph showing a change in image quality over time. tb1 is the time when the preview channel completes the initial buffering to serve the image of the minimum quality. And even after this, the preview channel continuously receives multimedia to provide better quality video to tb2 and better quality video to tb3 than tb2. For this purpose, an SVC service can be applied.

Claims

If a user who wants to change the channel is not the preview channel serviced by the existing multicast, the service is provided by the unicast service only for the user to provide the preview service for only one user.