[FFmpeg-devel] [PATCH 07/10] lavf: document that AVStream::codecpar may be modified by lavf after avformat_write_header(). This is assumed not to break API because it's already true (see e.g. matroskaenc handling of new AAC extradata)

[Rodger Combs]

Could we just declare that lavf can update extradata (and nothing else) if it gets packets with new-extradata side-data? If not, I suppose we could either add something to AVStreamInternal, or do something internal in check_bitstream (and update movenc and matroskaenc, as both exhibit this behavior right now).

> On Mar 15, 2018, at 20:04, Hendrik Leppkes <h.leppkes at gmail.com> wrote:
> 
> On Fri, Mar 16, 2018 at 12:29 AM, Michael Niedermayer
> <michael at niedermayer.cc <mailto:michael at niedermayer.cc>> wrote:
>> On Wed, Mar 14, 2018 at 01:24:42AM -0500, Rodger Combs wrote:
>>> ---
>>> libavformat/avformat.h | 3 ++-
>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>>> index 9e87d6cdac..5f0ebfc114 100644
>>> --- a/libavformat/avformat.h
>>> +++ b/libavformat/avformat.h
>>> @@ -1006,7 +1006,8 @@ typedef struct AVStream {
>>>      *
>>>      * - demuxing: filled by libavformat on stream creation or in
>>>      *             avformat_find_stream_info()
>>> -     * - muxing: filled by the caller before avformat_write_header()
>>> +     * - muxing: filled by the caller before avformat_write_header();
>>> +     * -         may be modified by libavformat afterwards
>>>      */
>> 
>> a generic "anything can change" is not really practical
>> a user app would have to check every field of codecpar and possibly insert
>> video scalers if resoluton changed, or all kinds of other filters and even
>> different encoders if codec_id was adjusted ...
>> 
> 
> I generally don't like this either. codecpar describes the codec as
> given to the muxer by the user. The muxer has no business changing
> things around in it.
> If it can derive better values somehow, let it store it internally somewhere.
> 
> - Hendrik
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel at ffmpeg.org <mailto:ffmpeg-devel at ffmpeg.org>
> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel <http://ffmpeg.org/mailman/listinfo/ffmpeg-devel>