[FFmpeg-devel] [PATCH] lavc/hevc_parser: add 4 bytes startcode condition in hevc_find_frame_end

[Fu, Linjie]

> -----Original Message-----
> From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf
> Of Michael Niedermayer
> Sent: Thursday, November 29, 2018 02:14
> To: FFmpeg development discussions and patches <ffmpeg-
> devel at ffmpeg.org>
> Subject: Re: [FFmpeg-devel] [PATCH] lavc/hevc_parser: add 4 bytes
> startcode condition in hevc_find_frame_end
> 
> On Tue, Nov 27, 2018 at 08:16:55PM +0800, Linjie Fu wrote:
> > The startcode before VPS,SPS,PPS and the first NALU in an AU is 4 bytes.
> > Blindly taking the startcode as 3 bytes will leave 0x00 in last packet
> > and may lead to some warnings in parse_nal_units when s->flags is set to
> > PARSER_FLAG_COMPLETE_FRAMES.
> >
> > Add 4 bytes startcode condition in hevc_find_frame_end.
> > Modify the code to print the buf_size like in H264 and reduce the
> duplication.
> >
> > Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> > ---
> >  libavcodec/hevc_parser.c | 15 ++++++++++-----
> >  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> breaks
>  make fate-hevc-bsf-mp4toannexb
> TEST    hevc-bsf-mp4toannexb
> --- -	2018-11-28 19:12:47.869732022 +0100
> +++ tests/data/fate/hevc-bsf-mp4toannexb	2018-11-28
> 19:12:47.864276885 +0100
> @@ -1 +1 @@
> -1873662a3af1848c37e4eb25722c8df9
> +73019329ed7f81c24f9af67c34c640c0
> Test hevc-bsf-mp4toannexb failed. Look at tests/data/fate/hevc-bsf-
> mp4toannexb.err for details.
> make: *** [fate-hevc-bsf-mp4toannexb] Error 1
> 

Investigate the root cause:

In fate test:
Step 1. ffmpeg -i hevc-conformance/WPP_A_ericsson_MAIN10_2.bit -c copy -flags +bitexact hevc-mp4.mov
Step 2. ffmpeg -i hevc-mp4_after.mov -c:v copy -fflags +bitexact -f hevc hevc.out
Step3. md5sum and compared with the reference

Compare the output file in Step 1 before and after the patch, and found it changed:
-rw-r--r-- 1 root     root     68460 11月 29 11:23 hevc-mp4_after.mov
-rw-r--r-- 1 root     root     68507 11月 29 11:31 hevc-mp4_before.mov

Compare the original file with two output files:
SUFFIX_SEI bit information in  the first frame for example :

WPP_A_ericsson_MAIN10_2.bit: { 50 01 84 31 00 19 39 77 d0 7b 3f bd 1e 09 38 9a 79 41 c0 16 11 da 18 aa 0a db 2b 19 fa 47 3f 0f 67 4a 91 9c a1 12 72 67 d6 f0 8f 66 ee 95 f9 e2 b9 ba 23 9a e8 80 }

hevc-mp4_before.mov: { 50 01 84 31 00 19 39 77 d0 7b 3f bd 1e 09 38 9a 79 41 c0 16 11 da 18 aa 0a db 2b 19 fa 47 3f 0f 67 4a 91 9c a1 12 72 67 d6 f0 8f 66 ee 95 f9 e2 b9 ba 23 9a e8 80 00 }

hevc-mp4_after.mov: { 50 01 84 31 00 19 39 77 d0 7b 3f bd 1e 09 38 9a 79 41 c0 16 11 da 18 aa 0a db 2b 19 fa 47 3f 0f 67 4a 91 9c a1 12 72 67 d6 f0 8f 66 ee 95 f9 e2 b9 ba 23 9a e8 80 }

Before applying the patch, the output file has an extra 0x00 at the end of SUFFIX_SEI (because of blindly taking startcode as 3 bytes and left one byte).
After applying the patch, the output file has the same bit info like the original file.
So, I think this patch works.

Thanks,
- Linjie