KR100673253B1 - Apparatus for Video Decoding - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video decoding apparatus and method, and more particularly, when a system is changed and a system time clock (STC), which is a reference of a time stamp, is changed, video that has already been received through a previous channel. The data is decoded and output without using the time stamp, and when the video data processing of the previous channel is completed, the data is decoded and outputted using the time stamp again.

Accordingly, the video data decoding of the previous channel and the video data decoding of the current channel are continuously performed in the same buffer during channel switching, so that the seamless display of the screen is possible and the channel switching time is shortened even during channel switching. have.

Digital TV, Video Decoder, Channel Switching, STC, Time Stamp

Description

Video decoding device {Apparatus for Video Decoding}

1 is an example of a digital TV to which a video decoding apparatus of the present invention is applied;

2 is an overview of the status of a video video bit stream buffer;

3 is an embodiment of a video decoding method according to the present invention;

4 is an example of a state of a frame memory;

5 is another example of a state of a frame memory;

6 is a relationship between decoding time and display time.

* Explanation of symbols for main parts of the drawings

11: tuner 12: system decoder

13: audio decoder 14: speaker

15: Video Bit Stream Buffer 16: Video Decoder

17: frame memory 18: video post-processing unit

19: display device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video decoding apparatus and method, and more particularly, to enable channel switching to be performed smoothly and in a short time without any dark screen processing during channel switching.

By using digital broadcasting technology, data such as voice, video, and text can be efficiently compressed and transmitted, thereby reducing the amount of data required for one channel and providing more information.

On the other hand, Digital TV System is developing into a system capable of interactive or interactive service that can directly reflect the needs of viewers, and return channel such as modem, internet, leased line connected to digital TV system. ) May inform the broadcast service provider of the request of the viewer and return the appropriate service to the viewer. For example, a digital TV screen allows users to shop, order, and check delivery of products related to a broadcast program, and various interactive services such as ordering and paying for a movie that viewers want in a movie channel classified by various themes. It is possible.

Video compression for digital broadcasting uses the Moving Picture Expert Group (MPEG) standard. The basic framework of this compression scheme is the use of techniques to remove spatial and temporal redundancy. To remove spatial redundancy, the data in the pixel domain is transformed into the frequency domain and quantized, which removes high-frequency components that are not visually sensitive and reduces the amount of data to be transmitted.

As a method of eliminating temporal redundancy, motion estimation and compensation techniques are used. A portion having a pixel value similar to the current image frame is found from the reference image frame and encoded into a motion vector, and the remainder is encoded by frequency transforming the difference value.

Video frame types of the MPEG video include I (Intra), P (Predictive), and B (Bi-predictive). In case of I frame, it is a video frame that can be restored by itself without requiring another reference frame, P frame requires one reference frame decoded first in decoding order, and B frame according to decoding order. First we need two decoded reference frames. Since the I frame can be restored by itself without a reference frame, the video decoder is refreshed by eliminating error accumulation due to motion compensation.

In general, I frames need to be spaced to some degree. In general, one I frame is transmitted for each video sequence or group of pictures (GOP) layer. The time interval is generally about 0.5 seconds. This constant interval serves as a constraint to determine the start point of the video when the channel is switched in the digital TV receiver.

When the digital TV channel is switched, channel switching delay time is required according to the characteristics of the previous channel and the channel to be switched. Most channel switching requires switching of the system clock. The system clock is used to control the internal video buffer and to synchronize video and audio.

In the case of voice, it does not generally use a buffer to store the compressed data. Therefore, if the decoding time and the output time are decoded without synchronizing with the system clock, they can be output through the speaker immediately after the channel switching.

However, in case of an image, a time stamp (DTS: Presentation Time Stamp) based on a system clock is used to read, decode data from a video bit stream buffer, and output a restored video. In addition, when channel switching is performed, a process of initializing an internal STC counter by the system clock is performed. After the system clock has stabilized, a sequence of steps is needed to free the data from the previous channel stored in the video bit stream buffer, find the I frame from the new video sequence, and decode it. In other words, if the system clock is changed by channel switching, the video bit stream buffer is reset and emptied, and all video decoder operations are stopped and the decoding state is reset to prepare for decoding the next video sequence.

When a new video bit stream input from the converted channel is stored in a buffer, I frames are found and decoded, and subsequent video frames are sequentially decoded and output by matching time stamps (DTS and PTS). Is done. This series of processes, as mentioned above, requires a certain amount of time, and most of the channel switching time is a video delay time.

In addition, in terms of frame memory, a memory storage area may change when channel switching is performed.

That is, when two channels of video have different image frame sizes, a new memory storage area of the previous channel and the switching channel overlaps. In this case, the screen output to the display device is mostly damaged.

Therefore, in order to avoid outputting a damaged screen, a dark screen or a different screen is displayed instead of the video delay time according to channel switching. As a result, a smooth and natural channel switching cannot be performed, and inconveniences such as the screen are broken from the viewer's point of view occur.

Accordingly, the present invention has been made to solve the above problems, and can reduce the video delay time and support seamless channel switching of the screen without processing a dark screen or displaying another screen during the video delay time according to the channel switching. It is an object of the present invention to provide a video decoding apparatus and method.

In order to achieve the above object, the video decoding apparatus according to the present invention separates an audio bit stream and a video bit stream from a received bit stream, and uses a system time clock (STC) that is a reference of a time stamp. A system decoder for recovering a system time clock; A video bit stream buffer for temporarily storing a video bit stream output from the system decoder; And a video decoder which decodes the video data of the video bit stream buffer using the time stamp, but decodes the data without using the time stamp for a certain 'hold time' when the STC is changed. A frame memory for storing image frame information decoded by the video decoder; And a video post-processing unit outputting image frame information stored in the frame memory to a display device.

If the STC is changed, the video decoder keeps the video frame information necessary for decoding the video frame of the previous channel in the frame memory until the holding time elapses, and the video frame information of the converted new channel is stored in the video memory. It can be configured to store sequentially in the other areas of the frame memory. The video decoder deletes information related to an image frame of a previous channel stored in the frame memory after the holding time elapses.

A video decoding method according to the present invention includes the steps of changing the system time clock (STC) through channel switching; Turning off the time stamp checking function of the video decoder; Decoding video data of the video bit stream buffer without using a time stamp for a predetermined 'hold time'; Turning on a time stamp checking function of a video decoder when the holding time elapses; Decoding the video data of the video bit stream buffer using a time stamp.

The holding time is preferably configured to have a value equal to or greater than a maximum delay time of the video bit stream buffer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The video decoding apparatus according to the present invention will be described with reference to the digital TV system shown in FIG. 1.

The broadcast signal is received through the antenna, and a specific program or channel is selected through the tuner 11 and transmitted to the system decoder 12 in the form of a transport stream (TS).

The system decoder 12 collects program guide information from the transport stream TS, filters the audio and video information corresponding to the program selected by the viewer, and transmits the audio and video information to the audio decoder 13 and the video decoder 16, respectively. At this time, the format of the data delivered to the audio decoder 13 and the video decoder 16 is in the form of a packetized elementary stream (PES), and information useful for decoding such as time stamps (DTS, PTS) and elementary stream (ES) It is included.

In addition, the system decoder 12 restores the STC (System Time Clock), which is a reference of the system, from the PCR (Program Clock Reference), which is information contained in the transport stream TS, to the audio decoder 13 and the video decoder 16. To pass on. The STC may be used as a driving clock of the STC counter on which the audio decoder 13 and the video decoder 16 match and decode time stamps DTS and PTS.

The audio decoder 13 receives the audio PES from the system decoder 12, decodes the audio frame according to the PTS, and outputs the audio PES through the speaker 14.

Meanwhile, the video bit stream output from the system decoder 12 is once stored in the video bit stream buffer 15, and the video decoder 16 decodes the video data stored in the video bit stream buffer 15 to frame memory 17. ).

In particular, when the STC is changed in the system decoder 12, the video decoder 16 according to the present invention decodes the video data of the video bit stream buffer 15 without using a time stamp for a certain 'hold time'. When the retention time elapses, the video data of the video bit stream buffer 15 is decoded using the time stamp.

Here, the retention time means a time required to process all the video data of the previous channel remaining in the video bit stream buffer 15 when the channel is changed, and is set to a value equal to or greater than the maximum delay time of the video bit stream buffer 15. It is preferable. In addition, any method having the same meaning as applying a holding time may be used, such as comparing a DTS and an STC counter value to determine a predetermined condition and confirming that all video data of a previous channel has been processed. .

2 shows the state of the video bit stream buffer 15 when channel switching occurs. At time t1, channel switching occurs and the input video bit stream is switched, and the remaining data amount in the video bit stream buffer at that time is dn. When the data amount dn2 removed for decoding at time t2 is equal to dn, it is determined that video data of the previous channel is completely removed from the video bit stream buffer. Therefore, while the dt time video data of the previous channel is decoded, on the other hand, the video data of the converted current channel is also input.

At this time, since the video decoder 16 should not decode the video data of the previous channel using the new DTS and PTS, the video decoder 16 processes all the video data of the previous channel remaining in the video bit stream buffer 15. Until this time (during the holding time), it is to decode the video data of the previous channel stored in the video bit stream buffer 15 using only STC without checking the time stamp information.

When all the video data of the previous channel is processed, the video data of the new channel is normally decoded using the time stamp. That is, the retention time is preferably set to the time required to decode all the video data when the video bit stream buffer 15 has the most video data of the previous channel.

Frame memory 17 is a component that stores image frame information decoded by video decoder 16. Frame memory 17 is a frame for display and two frames used as reference for decoding another image frame. It is usually composed of memory.

The video post-processing unit 18 converts the image frame information decoded by the video decoder 16 and stored in the frame memory 17 to match the screen configuration of the display device 19 and displays the image on the screen. Examples of image conversion include screen size conversion, aspect ratio conversion, and display scan method conversion.

An embodiment of a video decoding method according to the present invention will be described with reference to FIG. 3.

When channel switching is made through the tuner 11 (S31), the system decoder 12 collects program information from the transport stream TS of the new channel and determines whether the system clock has been changed (S32). At this time, the system decoder 12 may determine whether the system clock is changed when the channel switching through the tuner 11 is made and the transport stream TS of the new channel starts to be input.

If the determination in step S32 has not changed the system clock (ie, the program has been encoded with the same system clock), then the video decoder 16 decodes the video data entering the video bit stream buffer 15 in a previous state. Continues to be performed continuously (S38).

However, if the system clock is changed as a result of the determination in step S32, the DTS and PTS check functions of the video decoder 16 are turned off (S33), initialized with a new system clock, and the video and audio PES corresponding to the selected program are filtered out. Resume the function (S34).

The video decoder 16 continuously decodes the video data of the previous channel remaining in the video bit stream buffer 15 (S35 and S36). At this time, since the DTS and PTS check functions are turned off in step S33, the video decoder 16 performs decoding without using the time stamp. That is, two bit streams based on different system clocks are mixed in the video bit stream buffer 15, and because of the discontinuity in the DTS and the PTS due to the change of the STC, the inspection of the DTS and the PTS is performed for continuous decoding. Should not.

At this time, the audio decoder 13 also decodes the audio frame and outputs it to the speaker 14 without checking the PTS.

On the other hand, if the video data of the previous channel is completely removed from the video bit stream buffer 15 (S36), the DTS and PTS check function of the video decoder is turned on again (S37), and the video decoder 16 receives the DTS and PTS information. Decode the video data of the new channel by using (S38).

At this time, the audio decoder 13 also controls to decode using the PTS so that the audio and video are synchronized. That is, when audio and video are output based on the same PTS based on the system clock, synchronization between them is achieved. However, since the PTS is not checked during the holding time during channel switching, the audio and video may not be synchronized during the holding time. However, it is possible to shorten the channel switching time and show more to the viewer as compared to processing the voice to mute and processing the video to the dark screen as in the prior art.

On the other hand, since the memory of the digital TV receiver is limited, decoding is performed while changing various memory maps according to the screen size of an image to be decoded. In this case, the frame memory 17 may be divided into a memory area for storing a reference frame and a memory area for temporarily storing a display, and additionally, a memory used by the video post-processing unit 18 is needed.

Since video frame information of the frame memory 17 is also mixed at the time of channel switching, a method of managing the frame memory 17 at the time of channel switching is necessary.

According to one embodiment of the present invention for effectively processing video frames mixed in the frame memory 17 at the time of channel switching, image frame information required for decoding the video frame of the previous channel until the retention time elapses may be stored in the frame memory ( The video frame information received in the current channel and stored in the current channel is sequentially stored in the other area of the frame memory 17. When the retention time has elapsed, the information related to the video frame of the previous channel stored in the frame memory 17 is deleted.

A method of managing the frame memory 17 will be described in more detail with reference to FIGS. 4 to 6.

FIG. 4 illustrates a state of change of the frame memory 17 when the size of an image frame is changed from a high definition (HD) to a standard definition (SD) according to channel switching. 4A shows a frame memory map for HD video before channel switching occurs. The frame memory 17 includes memory areas Fr1 and Fr2 for storing reference frames (eg, I and P), memory area Fr3 for display, and memory area Disp Fr used by the video post-processing unit 18. . Here, the memory area Disp Fr is used for Picture In Picture (PIP), On Screen Display (OSD) or graphics, and is configured to have one or more HD image frame sizes to give various display effects.

4B illustrates an intermediate process in which channel switching occurs and display switching occurs, and image frames New Fr1 to New Fr4 of new channels are stored while Fr1 and Fr2 are stored for image frame processing of the previous channel.

4C illustrates a memory map in which display switching is completed after channel switching. When all image frame processing of the previous channel is completed, all image frame information of the previous channel is deleted and no longer stored.

That is, when channel switching occurs from the HD video to the SD video, decoding is performed on the SD video while displaying the HD video.

FIG. 5 illustrates a state in which the frame memory 17 is changed when a channel transition occurs from an SD image to an HD image, and similarly to the switching process illustrated in FIG. Is preserved until

6 shows the decoding change time point t1 and the display change time point t2.

That is, since the decoding change point and the display change point are different from each other, each piece of information must be managed separately. In the general case, Fr1, Fr2, Fr3 in Fig. 4a must be preserved for the next display. Therefore, as shown in FIG. 4B, the decoded image frames New Fr1 to New Fr4 should be stored after securing the decoded image frame in the display frame area Dis Fr by simplifying the display effect and mode while preserving the previous image frames. After the time t2 passes, that is, after the display of the image frame of the previous channel is completed, the frames Fr1, Fr2, and Fr3 are used as memory areas for other purposes.

The present invention is not limited to the above-described embodiments and can be variously modified and implemented by those skilled in the art without departing from the technical spirit of the present invention.

According to the present invention, the video data decoding of the previous channel and the video data decoding of the current channel are continuously performed in the same buffer at the time of channel switching, thereby enabling seamless continuous display of the screen even during channel switching and shortening the channel switching time. It is effective. In particular, when switching channels, it is not necessary to provide a dark screen or a separate screen, so that the screen can be switched more naturally.

Claims (6)

A system decoder which separates an audio bit stream and a video bit stream from a received bit stream and recovers a system time clock (STC), which is a time stamp reference, and a video bit stream output from the system decoder. A video bit stream buffer for temporarily storing the video bit stream buffer, and a video decoder for decoding the video data of the video bit stream buffer using the time stamp, but without using the time stamp for a certain 'hold time' when the STC is changed. A frame memory for storing image frame information decoded by the video decoder, and a video post-processing unit for outputting image frame information stored in the frame memory to a display device; When the STC is changed, the video decoder keeps the image frame information necessary for decoding the image frame of the previous channel in the frame memory until the holding time elapses, and the image frame information of the current channel is stored in the frame. And store the data in a sequence in another area of the memory. The method of claim 1, The holding time is configured to have a value equal to or greater than a maximum delay time of the video bit stream buffer. delete The method of claim 1, And the video decoder is configured to delete information related to an image frame of a previous channel stored in the frame memory when the holding time elapses. delete delete

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