> On May 16, 2025, at 22:52, Timo Rothenpieler <t...@rothenpieler.org> wrote:
>
> On 16/05/2025 16:24, Zhao Zhili wrote:
>> From: Zhao Zhili <zhiliz...@tencent.com <mailto:zhiliz...@tencent.com>>
>> ffmpeg -i input.mp4 -c copy -tag:v av01 output.flv
>> [flv @ 0x143204080] Tag av01 incompatible with output codec id '225' (10va)
>
> I don't quite understand what causes this.
> Is this an issue when running on big endian architectures?
> I'm pretty sure I tested all combinations of codecs with muxing and demuxing,
> and never ran into that error.
The key point is when specify tag via command line, e.g., -tag:v av01, it’s
passed to AVCodecParameters codec_tag in little endian.
You didn’t see the error because without specify the tag explicitly, codec_tag
is copied
from AVOutputFormat codec_tag to AVCodecParameters codec_tag, so they are
the same.
Another example is codec_mp4_tags.
>
>> ---
>> libavformat/flvenc.c | 26 +++++++++++++++++---------
>> 1 file changed, 17 insertions(+), 9 deletions(-)
>> diff --git a/libavformat/flvenc.c b/libavformat/flvenc.c
>> index f026f0e53b..e92828b197 100644
>> --- a/libavformat/flvenc.c
>> +++ b/libavformat/flvenc.c
>> @@ -52,9 +52,9 @@ static const AVCodecTag flv_video_codec_ids[] = {
>> { AV_CODEC_ID_VP6, FLV_CODECID_VP6 },
>> { AV_CODEC_ID_VP6A, FLV_CODECID_VP6A },
>> { AV_CODEC_ID_H264, FLV_CODECID_H264 },
>> - { AV_CODEC_ID_HEVC, MKBETAG('h', 'v', 'c', '1') },
>> - { AV_CODEC_ID_AV1, MKBETAG('a', 'v', '0', '1') },
>> - { AV_CODEC_ID_VP9, MKBETAG('v', 'p', '0', '9') },
>> + { AV_CODEC_ID_HEVC, MKTAG('h', 'v', 'c', '1') },
>> + { AV_CODEC_ID_AV1, MKTAG('a', 'v', '0', '1') },
>> + { AV_CODEC_ID_VP9, MKTAG('v', 'p', '0', '9') },
>> { AV_CODEC_ID_NONE, 0 }
>> };
>> @@ -69,10 +69,10 @@ static const AVCodecTag flv_audio_codec_ids[] = {
>> { AV_CODEC_ID_PCM_MULAW, FLV_CODECID_PCM_MULAW >>
>> FLV_AUDIO_CODECID_OFFSET },
>> { AV_CODEC_ID_PCM_ALAW, FLV_CODECID_PCM_ALAW >>
>> FLV_AUDIO_CODECID_OFFSET },
>> { AV_CODEC_ID_SPEEX, FLV_CODECID_SPEEX >>
>> FLV_AUDIO_CODECID_OFFSET },
>> - { AV_CODEC_ID_OPUS, MKBETAG('O', 'p', 'u', 's') },
>> - { AV_CODEC_ID_FLAC, MKBETAG('f', 'L', 'a', 'C') },
>> - { AV_CODEC_ID_AC3, MKBETAG('a', 'c', '-', '3') },
>> - { AV_CODEC_ID_EAC3, MKBETAG('e', 'c', '-', '3') },
>> + { AV_CODEC_ID_OPUS, MKTAG('O', 'p', 'u', 's') },
>> + { AV_CODEC_ID_FLAC, MKTAG('f', 'L', 'a', 'C') },
>> + { AV_CODEC_ID_AC3, MKTAG('a', 'c', '-', '3') },
>> + { AV_CODEC_ID_EAC3, MKTAG('e', 'c', '-', '3') },
>> { AV_CODEC_ID_NONE, 0 }
>> };
>> @@ -348,7 +348,11 @@ static void write_metadata(AVFormatContext *s,
>> unsigned int ts)
>> }
>> put_amf_string(pb, "videocodecid");
>> - put_amf_double(pb, flv->video_par->codec_tag);
>> + uint32_t tag = flv->video_par->codec_tag;
>> + // check and convert to fourcc
>> + if (tag & 0xFFFFFF00)
>> + tag = av_bswap32(tag);
>> + put_amf_double(pb, tag);
>
> Shouldn't this be completely equivalent to having MKBETAG generate it in
> big-endian order from the get-go?
>
>> }
>> if (flv->audio_par) {
>> @@ -365,7 +369,11 @@ static void write_metadata(AVFormatContext *s, unsigned
>> int ts)
>> put_amf_bool(pb, flv->audio_par->ch_layout.nb_channels == 2);
>> put_amf_string(pb, "audiocodecid");
>> - put_amf_double(pb, flv->audio_par->codec_tag);
>> + uint32_t tag = flv->audio_par->codec_tag;
>> + // check and convert to fourcc
>> + if (tag & 0xFFFFFF00)
>> + tag = av_bswap32(tag);
>> + put_amf_double(pb, tag);
>> }
>> if (flv->data_par) {
>
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