Re: [FFmpeg-devel] [PATCH v1] avformat/imfdec: preserve stream information

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Pierre-Anthony Lemieux:
> On Sun, Jul 3, 2022 at 12:15 PM Andreas Rheinhardt
> <andreas.rheinhardt@outlook.com> wrote:
>>
>> Pierre-Anthony Lemieux:
>>> On Sun, Jul 3, 2022 at 11:28 AM Andreas Rheinhardt
>>> <andreas.rheinhardt@outlook.com> wrote:
>>>>
>>>> pal@sandflow.com:
>>>>> From: Pierre-Anthony Lemieux <pal@palemieux.com>
>>>>>
>>>>> As discussed at https://trac.ffmpeg.org/ticket/9818, the IMF demuxer does not
>>>>> currently preserve stream information such as language in the case of audio
>>>>> streams. This patch is modeled on copy_stream_props() at avformat/concatdec.c.
>>>>>
>>>>> ---
>>>>>  libavformat/imfdec.c | 5 +++++
>>>>>  1 file changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/libavformat/imfdec.c b/libavformat/imfdec.c
>>>>> index 71dfb26958..7aa66a06bf 100644
>>>>> --- a/libavformat/imfdec.c
>>>>> +++ b/libavformat/imfdec.c
>>>>> @@ -580,11 +580,16 @@ static int set_context_streams_from_tracks(AVFormatContext *s)
>>>>>              return AVERROR(ENOMEM);
>>>>>          }
>>>>>          asset_stream->id = i;
>>>>> +        asset_stream->r_frame_rate = first_resource_stream->r_frame_rate;
>>>>> +        asset_stream->avg_frame_rate = first_resource_stream->avg_frame_rate;
>>>>> +        asset_stream->sample_aspect_ratio = first_resource_stream->sample_aspect_ratio;
>>>>>          ret = avcodec_parameters_copy(asset_stream->codecpar, first_resource_stream->codecpar);
>>>>>          if (ret < 0) {
>>>>>              av_log(s, AV_LOG_ERROR, "Could not copy stream parameters\n");
>>>>>              return ret;
>>>>>          }
>>>>> +        av_dict_copy(&asset_stream->metadata, first_resource_stream->metadata, 0);
>>>>> +        ff_stream_side_data_copy(asset_stream, first_resource_stream);
>>>>>          avpriv_set_pts_info(asset_stream,
>>>>>                              first_resource_stream->pts_wrap_bits,
>>>>>                              first_resource_stream->time_base.num,
>>>>
>>>> Seems to me like one should use ff_stream_encode_params_copy here. Of
>>>> course, it would have to be renamed and moved if used in a demuxer.
>>>
>>> Would copy_stream_props() in concatdec.c need to be refactored as well?
>>>
>>
>> I often wondered about this. The problem with copy_stream_props is that
>> it is not only called during read_header, but lateron as well, but e.g.
>> the documentation of AVStream.side_data says that it is populated when
>> the stream is created and not later.
>> This issue does of course not exist in your case.
> 
> ff_stream_encode_params_copy() does not seem to set pts_wrap_bits,
> i.e. it does not call avpriv_set_pts_info().
> 

The reason for this is that pts_wrap_bits is irrelevant for muxing.

>>
>>> Note that, in the case of avformat/imfdec.c, AVStream::id is not
>>> copied across, so ff_stream_encode_params_copy() would need to be
>>> followed by asset_stream->id = i;
>>>
>>
>> Yeah, I know.
>>
>> - Andreas
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