[FFmpeg-devel] h264.c avcC file reading error on PPS with trailing zeros, with tiny patch attached

[Benoit Fouet]

Hi Michael,

Michael Niedermayer wrote:
> On Wed, Aug 13, 2008 at 03:41:05PM -0400, Francois Oligny-Lemieux wrote:
>   
>> Hi,
>>
>> In .mp4 files are saved the SPS and PPS. When ffmpeg decodes the .mp4 video
>> extradata, it should allow trailing zeros at the end of those NAL units.
>>
>> In original code, the SPS is decoded, then the PPS
>>
>>         // Decode sps from avcC
>>         cnt = *(p+5) & 0x1f; // Number of sps
>>         p += 6;
>>         for (i = 0; i < cnt; i++) {
>>             nalsize = AV_RB16(p) + 2;
>>             if(decode_nal_units(h, p, nalsize) < 0) {
>>                 av_log(avctx, AV_LOG_ERROR, "Decoding sps %d from avcC
>> failed\n", i);
>>                 return -1;
>>             }
>>             p += nalsize;
>>         }
>>         // Decode pps from avcC
>>         cnt = *(p++); // Number of pps
>>         for (i = 0; i < cnt; i++) {
>>             nalsize = AV_RB16(p) + 2;
>>             if(decode_nal_units(h, p, nalsize)   != nalsize) {
>>                 av_log(avctx, AV_LOG_ERROR, "Decoding pps %d from avcC
>> failed\n", i);
>>                 return -1;
>>             }
>>             p += nalsize;
>>         }
>>
>> The SPS part is OK because it just checks if decode_nal_units didn't fail.
>> The second part is different and less flexible because it requires that
>> decode_nal_unit consumes the same amount of bytes that were passed. I don't
>> know why both part were not coded the same. The problem is that this doesn't
>> pass when there are trailing zeros. So just making the second part's check
>> like the first one allows the decoding of .mp4 that have trailing zeros in
>> PPS (like the file I uploaded on
>> upload.mplayerhq.hu/MPlayer/incoming/HD4ED_au_720p60.03.mp4). Note
>> that QuickTime is able to
>> decode it, while FFmpeg fails; but with the patch, FFmpeg succeeds.
>>     
>
> patch ok (not that i think that a file needing it would be valid) but its
> more robust with the patch
>
> [...]
>   
>   

as you're working on h.264 these days, do you want to apply it yourself
or do you want me to do it ?

-- 
Benoit Fouet
Purple Labs S.A.
www.purplelabs.com