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

["zhilizhao(赵志立)"]

> On May 30, 2023, at 09:03, Lance Wang <lance.lmwang at gmail.com> wrote:
> 
> On Mon, May 29, 2023 at 10:16 PM Zhao Zhili <quinkblack at foxmail.com> wrote:
> 
>> From: Zhao Zhili <zhilizhao at tencent.com>
>> 
>> Signed-off-by: Zhao Zhili <zhilizhao at 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.

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.


> 
> 
>>             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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