Re: [FFmpeg-devel] [PATCH] avformat/mxfenc: add h264_mp4toannexb bitstream filter if needed when muxing h264

[Marton Balint <cus@passwd.hu>]

On Fri, 23 Feb 2024, Andreas Rheinhardt wrote:

> Marton Balint:
>> Partially fixes ticket #10395.
>> 
>> Signed-off-by: Marton Balint <cus@passwd.hu>
>> ---
>>  libavformat/mxfenc.c | 12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>> 
>> diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
>> index 61ed6fc3db..adc31c1cf4 100644
>> --- a/libavformat/mxfenc.c
>> +++ b/libavformat/mxfenc.c
>> @@ -3542,6 +3542,16 @@ static int mxf_interleave(AVFormatContext *s, AVPacket *pkt,
>>      return mxf_interleave_get_packet(s, pkt, flush);
>>  }
>> 
>> +static int mxf_check_bitstream(AVFormatContext *s, AVStream *st, const AVPacket *pkt)
>> +{
>> +    if (st->codecpar->codec_id == AV_CODEC_ID_H264) {
>> +        if (pkt->size >= 5 && AV_RB32(pkt->data) != 0x0000001 &&
>> +                              AV_RB24(pkt->data) != 0x000001)
>> +            return ff_stream_add_bitstream_filter(st, "h264_mp4toannexb", NULL);
>> +    }
>> +    return 1;
>> +}
>> +
>>  #define MXF_COMMON_OPTIONS \
>>      { "signal_standard", "Force/set Signal Standard",\
>>        offsetof(MXFContext, signal_standard), AV_OPT_TYPE_INT, {.i64 = -1}, -1, 7, AV_OPT_FLAG_ENCODING_PARAM, .unit = "signal_standard"},\
>> @@ -3623,6 +3633,7 @@ const FFOutputFormat ff_mxf_muxer = {
>>      .p.flags           = AVFMT_NOTIMESTAMPS,
>>      .interleave_packet = mxf_interleave,
>>      .p.priv_class      = &mxf_muxer_class,
>> +    .check_bitstream   = mxf_check_bitstream,
>>  };
>>
>>  const FFOutputFormat ff_mxf_d10_muxer = {
>> @@ -3656,4 +3667,5 @@ const FFOutputFormat ff_mxf_opatom_muxer = {
>>      .p.flags           = AVFMT_NOTIMESTAMPS,
>>      .interleave_packet = mxf_interleave,
>>      .p.priv_class      = &mxf_opatom_muxer_class,
>> +    .check_bitstream   = mxf_check_bitstream,
>>  };
>
> I sent the very same patch long ago [1]. Tomas Härdin opposed it [2],
> [3], because he sees stuff like this as hack.
>
> - Andreas
>
> [1]: https://ffmpeg.org/pipermail/ffmpeg-devel/2021-November/287638.html
> [2]: https://ffmpeg.org/pipermail/ffmpeg-devel/2021-November/287702.html
> [3]: https://ffmpeg.org/pipermail/ffmpeg-devel/2021-November/287703.html

Maybe we should discuss this again, define what is missing 
exactly, considering that we both think this is a step in the right 
direction.

The specs says this:

The Picture Element Values shall be the AVC NAL unit stream or the AVC 
byte stream. The bit streams carried in the Value field shall contain 
complete NAL units including their relevant parameter sets, other 
Supplemental Enhancement Information (SEI) and padding zeroes.

(https://pub.smpte.org/doc/st381-3/20170830-pub/)

Regards,
Marton
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