Re: [FFmpeg-devel] [PATCH] avformat/hlsenc: fix CODECS attribute of H.264

[Lance Wang <lance.lmwang@gmail.com>]

On Tue, May 30, 2023 at 11:09 AM "zhilizhao(赵志立)" <quinkblack@foxmail.com>
wrote:

>
>
> > On May 30, 2023, at 09:03, Lance Wang <lance.lmwang@gmail.com> wrote:
> >
> > On Mon, May 29, 2023 at 10:16 PM Zhao Zhili <quinkblack@foxmail.com>
> wrote:
> >
> >> From: Zhao Zhili <zhilizhao@tencent.com>
> >>
> >> Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
> >> ---
> >> libavformat/hlsenc.c | 14 ++++++++++++--
> >> 1 file changed, 12 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/libavformat/hlsenc.c b/libavformat/hlsenc.c
> >> index 871afb571b..1e0848ce3d 100644
> >> --- a/libavformat/hlsenc.c
> >> +++ b/libavformat/hlsenc.c
> >> @@ -355,9 +355,19 @@ static void write_codec_attr(AVStream *st,
> >> VariantStream *vs)
> >>
> >>     if (st->codecpar->codec_id == AV_CODEC_ID_H264) {
> >>         uint8_t *data = st->codecpar->extradata;
> >> -        if (data && (data[0] | data[1] | data[2]) == 0 && data[3] == 1
> &&
> >> (data[4] & 0x1F) == 7) {
> >> +        if (data) {
> >> +            const uint8_t *p;
> >> +
> >> +            if (AV_RB32(data) == 0x01 && (data[4] & 0x1F) == 7)
> >> +                p = &data[5];
> >> +            else if (AV_RB24(data) == 0x01 && (data[3] & 0x1F) == 7)
> >> +                p = &data[4];
> >> +            else if (data[0] == 0x01)  /* avcC */
> >> +                p = &data[1];
> >> +            else
> >> +                goto fail;
> >>
> >
> > how to reproduce the issue? I recall mpegts is annex b format and sps/pps
> > start code is 4 byte always.
>
> For example:
>
> ffmpeg -i foo.mp4 -c copy -hls_playlist_type vod -master_pl_name bar.m3u8
> test.m3u8
>
> 1. The input of hls muxer can be avcc
>
> 2. The output of hls muxer can be avcc too, with fmp4 segments.
>
>
Yes, this is the case. I had to add mp4toannexb bsf after the copy for avcc
input.  If we
don't add the format conversion, hevc may  have the same issue I guess.
Also we should
check the size of extradata.



> 3. Start code of SPS/PPS should be 0 0 0 1, however, 0 0 1 exist in wild.
> ff_isom_write_avcc() does the same:
>
>     /* check for H.264 start code */
>     if (AV_RB32(data) != 0x00000001 &&
>         AV_RB24(data) != 0x000001) {
>         avio_write(pb, data, len);
>         return 0;
>     }
>
> ff_isom_write_avcc() can be used here, and get/create CODECS attribute can
> be
> shared by multiple muxers. I won't go that further by now.
>
>
The next NALU checking is for SPS only, so one more byte is zero_byte. It's
required by specs:

zero_byte is a single byte equal to 0x00.

When any of the following conditions are true, the zero_byte syntax element
shall be present:

   -

   –  the nal_unit_type within the nal_unit( ) is equal to 7 (sequence
   parameter set) or 8 (picture parameter set),
   -

   –  the byte stream NAL unit syntax structure contains the first NAL unit
   of an access unit in decoding order, as specified in clause 7.4.1.2.3.





>
> >
> >
> >>             snprintf(attr, sizeof(attr),
> >> -                     "avc1.%02x%02x%02x", data[5], data[6], data[7]);
> >> +                     "avc1.%02x%02x%02x", p[0], p[1], p[2]);
> >>         } else {
> >>             goto fail;
> >>         }
> >> --
> >> 2.25.1
> >>
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