[FFmpeg-devel] [PATCH] movenc: enable writing of interlace information back to the 'fiel' atom.

[Tim Nicholson]

On 18/10/12 16:33, Michael Niedermayer wrote:
> On Thu, Oct 18, 2012 at 11:26:13AM +0100, Tim Nicholson wrote:
>> Currently interlace information is carried all the way through the
>> chain, being modified as required by options such as "-top" and filters
>> such as "setfield" but is then ignored when it comes to setting the
>> "fiel" atom, which is mandated for some codecs.
>>
>> This patch updates the mov style interlace information from ffmpeg's
>> internal flags enabling the atom to be written.
>>
>> Passes Fate.
>> -- 
>> Tim
>>
> 
>>  movenc.c |    5 +++++
>>  1 file changed, 5 insertions(+)
>> 5ca2cc166967a4bb7d2dd944cdadfb23378b43c4  0001-movenc-enable-writing-of-interlace-information-back-.patch
>> From 49411c0f39fa95c645b630f3fd51a93bcf39a0ce Mon Sep 17 00:00:00 2001
>> From: Tim Nicholson <Tim.Nicholson at bbc.co.uk>
>> Date: Thu, 18 Oct 2012 11:17:12 +0100
>> Subject: [PATCH] movenc: enable writing of interlace information back to the
>>  'fiel' atom.
>>
>> ---
>>  libavformat/movenc.c |    5 +++++
>>  1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/libavformat/movenc.c b/libavformat/movenc.c
>> index 0b0bf83..b422b38 100644
>> --- a/libavformat/movenc.c
>> +++ b/libavformat/movenc.c
>> @@ -1103,6 +1103,11 @@ static int mov_write_video_tag(AVIOContext *pb, MOVTrack *track)
>>      avio_wb32(pb, 0); /* Data size (= 0) */
>>      avio_wb16(pb, 1); /* Frame count (= 1) */
>>  
>> +    /* Set AVCodecContext.field_order to match current interlace status
>> +       this is used to control the writing of the "fiel" atom */
>> +    if (track->enc->coded_frame->interlaced_frame)
>> +        track->enc->field_order = track->enc->coded_frame->top_field_first ? AV_FIELD_TB:AV_FIELD_BT;
> 
> that looks quite odd, for example assume there is no decoder and
> encoder, but just stream copy, coded_frame will be NULL in that case.

I originally tested for track->enc->coded_frame but never found an
occasion where it was NULL so took it back out as in the case of a
stream copy the field_order is preserved anyway, forgetting that in this
case it would be NULL, doh! :(

> or consider the encoder (which can run in a seperate thread) frees
> coded_frame somewhere short before top_field_first is accessed.

Ahh, your right, I hadn't considered threading, and as I said in my
tests it never happened that way. However this is a more serious issue.
Presumably then there is no way to avoid doing it in the coder rather
than the muxer? I was trying to avoid having to add something to all
relevant coders..


> 
> 
> [...]
> 
> 
> 
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-- 
Tim