[FFmpeg-devel] [PATCH] avformat/yuv4mpegenc: simplify writing the header

[James Almer]

On 9/9/2020 7:54 PM, Michael Niedermayer wrote:
> On Thu, Sep 03, 2020 at 03:55:04PM -0300, James Almer wrote:
>> Actually write it in yuv4_write_header() instead of with the first
>> packet.
>>
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>>  libavformat/yuv4mpegenc.c | 35 ++++++++++++++---------------------
>>  1 file changed, 14 insertions(+), 21 deletions(-)
> 
> This changes the written header
> for example:
> ./ffmpeg  -i ~/tickets/2190/clip.yuv -bitexact testbad.y4m
> 
> YUV4MPEG2 W720 H480 F30000:1001 Ip A10:11 C411 XYSCSS=411
> vs
> YUV4MPEG2 W720 H480 F30000:1001 Ib A10:11 C411 XYSCSS=411

If I'm reading this right, ffmpeg.c changes the output AVCodecParameters
struct (In this case, field_order) after calling avformat_write_header()
but before writing a packet, which is wrong.

We could revert this change (And the one by Andreas that came after it),
but perhaps ffmpeg.c should be fixed to not violate the API instead.