KR20060083312A - Decoding method of digital broadcasting receiver - Google Patents

Abstract

The present invention relates to a decoding method of a digital broadcast receiver that performs synchronization error correction through control of a decoder buffer during A / V synchronization in an A / V decoder when a real time broadcast is performed in a digital broadcast receiver.

The present invention provides a method for decoding data input in units of an access unit (AU), obtaining a delay time from a difference between a current STC and a PTS of the AU after decoding, and calculating an error range on a difference between a current PTS and a previous PTS. Estimating the considered threshold value, if the delay time is greater than the threshold value, replacing the delay time with a difference between the current PTS and the previous PTS value, waiting for the delay time, and outputting decoded data. It provides a decoding method of a digital broadcast receiver comprising a.

Therefore, it is possible to prevent the overflow and underflow of the buffer by decoding at the appropriate time through the buffer control of the decoder.

Buffer, Decoding, Error Correction, STC, PTS

Description

Decoding method of digital broadcasting receiver

1 is a diagram illustrating time of playing video and audio sampled at different sample rates in the related art.

2 is a flowchart illustrating a method of synchronizing decoded audio and video in a digital broadcast receiver according to the present invention.

3A and 3B show a first embodiment in which PTSs and STCs are represented on the time axis;

4A and 4B show a second embodiment representing PTS and STC on the time axis.

The present invention relates to a decoding method of a digital broadcast receiver, and more particularly, to a synchronization error correction and decoder buffer control method for A / V synchronization in an A / V decoder of a digital multimedia broadcasting receiver.

Streams of digital multimedia broadcasting (DMB) use a common system clock to synchronize video and audio while multiplexing packets. The video and audio decoders play back at each presentation time stamp (PTS), which synchronizes the video and audio.

1 is a diagram illustrating a time for playing video and audio sampled at different sampling rates in the related art.

In the case of an ideal decoder, it can be assumed that it takes no time to decode the signal, and that the delay in transmission is fixed. In practice, such a decoder does not exist and is sometimes affected by the delay in decoding. May affect.

Also, in the digital multimedia broadcasting system, the common clock of the decoder system is referred to by the video and audio decoder, and playback is performed according to the reproduction reference time (PTS) determined by the encoder.

However, the above-described decoding method of the conventional digital broadcasting receiver has a problem that overflow and underflow of the buffer occurs when the decoding is not performed at an appropriate time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide synchronization error correction through control of a decoder buffer during A / V synchronization in an A / V decoder when real-time broadcasting is performed in a digital broadcast receiver. It is to provide a decoding method of a digital broadcast receiver.

In order to achieve the above object, the present invention is to decode the data input in units of an access unit (AU), to obtain a delay time from the difference between the current STC and the PTS of the AU after decoding, Estimating a threshold value considering an error range with respect to a previous PTS difference, replacing the delay time with a current PTS difference and a previous PTS difference value if the delay time is larger than the threshold value, waiting for the delay time, and then decoding It provides a decoding method of a digital broadcast receiver comprising the step of outputting the data.

And if there is an STC error, correcting the STC error, and determining whether the delay time is less than half of the STC maximum value.

Therefore, according to the present invention, the decoding is performed at an appropriate time through the buffer control of the decoder so that overflow and underflow of the buffer can be prevented. It is possible to apply to video and audio synchronization method in the decoder such as digital multimedia broadcasting that follows MPEG system because it processes in consideration of the situation.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can be specifically realized for the above purpose.

2 is a flowchart illustrating a method of synchronizing decoded audio and video in a digital broadcast receiver according to the present invention.

The present invention is largely divided into three parts.

In the first part, after decoding the access unit (AU), the current system time clock (STC) and the presentation time stamps (PTS) of the AU are set and the error of the set value is estimated.

 The second part is to obtain a delay (Delta delay), which is the difference between the PTS and the STC, correct the delay error, and set a timer of a processor used by the decoder.

 Lastly, a delay is output in response to a timer set in the decoder of the decoder.

Learn more about each step below.

First, a result frame of an access unit (AU) decoded from the decoder of the DMB receiver is stored in the output delay buffer (S10).

The PTS of the input AU is checked, and the STC is checked from the system decoder (S20).

After checking the STC and the PTS, it is determined whether there is an error in the STC (S30). If there is an error in the STC, the STC is corrected (S40). If there is no error in the STC, the delay time is the absolute difference between the PTS and the STC. (Delta delay, 'dt') and a threshold which is a period of the PTS is calculated (S50).

In this case, the threshold value may be corrected by giving an error range ε.

In the case of real-world DMB systems, many exceptions occur in obtaining dt. The information for synchronizing video and audio is also the object of the present invention to provide a solution in case of various exceptions. Hereinafter, various exceptions will be described in detail as follows.

3A and 3B are diagrams illustrating a first embodiment in which PTSs and STCs are represented on a time axis.

3A and 3B, the horizontal axis represents an absolute time as the processor proceeds. The vertical axis represents the set values of the PTS and STC. Since the STC changes every 24 hours, it is normal to follow the clock counter guide line.

Here, the star point of FIGS. 3A and 3B is a value of the PTS inserted during encoding, and is a point in time when the process reaches the absolute time on the horizontal axis, the decoded data is output. On the other hand, the round point is a reference value for comparing the absolute time corresponding to the PTS with the STC obtained when the decoder finishes decoding the data.

Therefore, the decoded data is output only when the STC value is equal to the PTS value. However, in the present invention, the difference between the STC and the PTS is converted to a value corresponding to the clock of the processor used by the decoder and delayed.

Fig. 3A shows the PTS and STC in the ideal case, and shows that the decoding is always performed before the playback time (PTS) and delayed by the playback time before being output. In this case, processing is important at the end of STC cycle, so the calculation of delay time is as follows.

dt = (PTS-STC + MAX)% MAX

In Equation 1,% represents a modulus operation, and MAX represents a maximum value of the STC. And dt is greater than zero.

After the step S50, it is determined whether the delay time is less than MAX / 2 (S60). If the delay time is greater than MAX / 2, the playback time is past, and thus the playback time is immediately displayed (S100).

In relation to FIG. 3B, dt should be smaller than MAX / 2 in order to determine when the PTS has passed the PTS due to the delay of the decoder.

If the delay time is less than MAX / 2 in the step S60, it is determined whether the delay time is smaller than a threshold (S70).

DMB video has a constant sampling rate of up to 30 FPS. Therefore, the PTS for each program has a substantially constant period. Therefore, since the delay time between AUs should be shorter than their periods, these periods should be used as thresholds, but the error range ε can be corrected for errors.

Threshold = PTS _current  -PTS _previous  + ε

The PTS _current Is the current PTS and PTS _previous is the previous PTS.

If the delay time is less than the threshold value in step S70, the delay time is counted by the CPU timer (S90). If the delay time is greater than the threshold value, the delay time is corrected (S80).

After the step S90, the AU is displayed (S100).

4A and 4B are diagrams illustrating a second embodiment in which PTSs and STCs are represented on a time axis.

4A is a case where the STC value shows a larger difference than expected, and the cause may be considered as follows. First, if the program time reference (PCR) is changed, that is, if the program is changed, the base of the time is changed. In this case, it is possible to check that the basis of time has changed through the HOST system.

offset = PTS _One  -STC ₂

In Equation 3, 1 and 2 mean different time bases.

The offset is valid until the value of the PTS returns to the base of the same time.

The STC value corrected in step S40 is obtained by using the correction value obtained in Equation 3 as follows.

STC _One  = STC ₂ + offset

In addition, when a value larger than the MAX value is referred, it is determined that the STC value is an error and the STC is requested again.

4B is a case where the PTS is set larger than the expected value. In this case, as described above, the constraint is not greater than the periodic difference (threshold) between the PTSs.

By default, you have to wait for the delay time (Delta_delay) to match the time you want to print. The delay value depends on the STC and the PTS. When the error of these values mentioned above actually causes an error in the time that the processor has to wait for the output, it should be corrected.

In order to determine the error that occurred, threshold is set.If Delta_delay is smaller than the threshold, delay value is delayed by Delta_delay and output (S90). Otherwise, delay time (Delta_delay) is Correct (S80).

In addition, since the reproduction time has a relatively constant time interval as shown in FIG. 1, the difference between the values of the PTS and the STC is corrected so as not to be larger than this. The correction method uses the data of the previous PTS.

In this regard, the interval of the PTS (ie, the interval of output time) is preferably constant at 33 msec for video at 30 FPS. Therefore, in the above case, the delay time Delta_delay is calculated to be output at a time point 33 msec based on a time point previously output.

PTS_INTERVAL = 33 msec (for video)

Current_CPU_CLOCK = GetCPUClock ();

Delta_delay = (Previous_CPU_CLOCK + PTS_INTERVAL)-Current_CPU_CLOCK;

Wait for Delta_delay seconds .

update Previous_CPU_CLOCK = Current_CPU_CLOCK;

Equation 5 is a method for correcting the delay time (Delta_delay) of the step S80 and waits for the delay time and outputs the correction.

The present invention is not limited to the above-described embodiments, and as can be seen in the appended claims, modifications can be made by those skilled in the art to which the invention pertains, and such modifications are within the scope of the present invention.

The decoding method effect of the digital broadcast receiver according to the present invention described above is as follows.

First, the present invention can decode at an appropriate time through the buffer control of the decoder to prevent the overflow and underflow of the buffer.

Second, since the present invention processes the decoded video and audio signals in consideration of the actual decoder situation, the present invention can be applied to the synchronization method of video and audio in a decoder such as a digital multimedia broadcasting according to the MPEG system.

Claims (5)

(a) decoding data input in units of an access unit (AU); (b) obtaining a delay time from the difference between the current STC and the PTS of the AU after decoding in step (a), and estimating a threshold value considering the error range in the difference between the current PTS and the previous PTS; (c) if the delay time is greater than the threshold, replacing the delay time with a current PTS difference value; and (d) waiting for the delay time, and then outputting the decoded data. The method of claim 1, And if there is an error in the STC, correcting the STC error. The method of claim 1, And wherein the delay time is obtained by performing a modulus operation on the difference between the current STC and the PTS of the AU. The method of claim 1, And determining whether the delay time is less than half of the STC maximum value. The method of claim 1, wherein step (d) A decoding method of a digital broadcasting receiver, characterized by setting a timer of a processing apparatus used by a decoding unit, and outputting after delaying an AU according to the set timer.

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