[FFmpeg-devel] [PATCH] ffmpeg: fix setting field_order during muxing

[James Almer]

On 8/10/2017 5:21 AM, Hendrik Leppkes wrote:
> On Thu, Aug 10, 2017 at 4:43 AM, James Almer <jamrial at gmail.com> wrote:
>> AVFrame.top_field_first doxy states
>>
>> "If the content is interlaced, is top field displayed first."
>>
>> And AVFieldOrder doxy defines:
>>     AV_FIELD_TB,          //< Top coded first, bottom displayed first
>>     AV_FIELD_BT,          //< Bottom coded first, top displayed first
>>
>> Fixes ticket #6577
>>
> 
> Isn't top coded first in most codecs? So maybe it should use TT (top
> coded and displayed first), and TB (top coded first, bottom displayed
> first)?

I can make it TT/TB if that's preferred, but it would be as much of a
guess as it currently is.

> I suppose that difference between coding order might be highly codec
> dependent, though.

I don't know. ffmpeg.c right now is using TT/BB for mjpeg only, so it
has at least one codec specific case.

A quick grep shows codecs like h264, vc1 and canopus using TT/BB, and
ffv1 using TT/TB, so someone more familiar with this might want to take
a look at it and add some other cases as required, at least for codecs
supported in containers that care about the contents of
AVFormatContext.field_order (matroska, mov, etc).

> 
> - Hendrik
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