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

[Michael Niedermayer]

On Thu, Oct 18, 2012 at 05:13:49PM +0100, Tim Nicholson wrote:
> 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..

the user app could set it before the encoder, but the dox would
need to be updated

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No great genius has ever existed without some touch of madness. -- Aristotle
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