[FFmpeg-devel] [PATCH] change frame_aspect_ratio to AVRational

[Michael Niedermayer]

On Thu, Jun 11, 2009 at 09:44:23PM -0700, Baptiste Coudurier wrote:
> On 6/11/2009 3:34 PM, Michael Niedermayer wrote:
> > On Thu, Jun 11, 2009 at 03:06:54PM -0700, Baptiste Coudurier wrote:
> >> On 6/11/2009 1:14 PM, Michael Niedermayer wrote:
> >>> On Thu, Jun 11, 2009 at 11:36:31AM -0700, Baptiste Coudurier wrote:
> >>>> On 6/11/2009 4:27 AM, Michael Niedermayer wrote:
> >>>>> On Wed, Jun 10, 2009 at 09:23:40PM -0700, Baptiste Coudurier wrote:
> >>>>>> Hi
> >>>>>>
> >>>>>> $subject, mainly to avoid using double which behaves not correctly
> >>>>>> when using 16:9 commandline.
> >>>>> [...]
> >>>>>> @@ -3012,7 +3012,8 @@
> >>>>>>          st->stream_copy = 1;
> >>>>>>          video_enc->codec_type = CODEC_TYPE_VIDEO;
> >>>>>>          video_enc->sample_aspect_ratio =
> >>>>>> -        st->sample_aspect_ratio = av_d2q(frame_aspect_ratio*frame_height/frame_width, 255);
> >>>>>> +        st->sample_aspect_ratio =
> >>>>>> +            av_mul_q(frame_aspect_ratio, (AVRational){ frame_height, frame_width });
> >>>>>>      } else {
> >>>>>>          const char *p;
> >>>>>>          int i;
> >>>>>> @@ -3039,7 +3040,8 @@
> >>>>>>  
> >>>>>>          video_enc->width = frame_width + frame_padright + frame_padleft;
> >>>>>>          video_enc->height = frame_height + frame_padtop + frame_padbottom;
> >>>>>> -        video_enc->sample_aspect_ratio = av_d2q(frame_aspect_ratio*video_enc->height/video_enc->width, 255);
> >>>>>> +        video_enc->sample_aspect_ratio =
> >>>>>> +            av_mul_q(frame_aspect_ratio, (AVRational){ frame_height, frame_width });
> >>>>>>          video_enc->pix_fmt = frame_pix_fmt;
> >>>>>>          st->sample_aspect_ratio = video_enc->sample_aspect_ratio;
> >>>>>>  
> >>>>> previously these where limited to 255/255 now they arent anymore, i think
> >>>>> some codecs dont support arbitrary fractions
> >>>> Ok, quick survey:
> >>>> theora encoder supports rational.
> >>>> h264 supports rational on 16bits.
> >>>> libxvid indeed checks for 255/255.
> >>>> mpeg12 converts back to float and match supported ones.
> >>>> mjpeg is rational on 16bits.
> >>>> h263/mpeg4 sar is rational on 8bits.
> >>>>
> >>>> Ok to add av_reduce to codecs needing it ?
> >>> encoders should not second guess the user
> >>> i mean if they accept a 300/301 then they should either store that or
> >>> if they cannot then fail
> >>>
> >>> it seems to me the current code is fine, is your patch fixing something
> >>> besides changing float to AVRational ?
> >>> if not we maybe could just keep it as it is
> >> Yes it keeps current par when converting when par > 255.
> >> resolution 720x512 DAR 16:9 PAR 512:405.
> >>
> >> mov can store this perfectly, codec par must be equal to stream par
> >> and current code alters both.
> >>
> >> Stream #0.0: Video: mpeg2video, yuv422p, 720x512 [PAR 67:53 DAR
> >> 3015:1696], q=2-31, 30000 kb/s, 90k tbn, 29.97 tbc
> >>
> >> Even with stream copy, mov can store rational on 32bits.
> >> and H.264 supports this exact PAR corresponding to DAR.
> >>
> >> Can we please apply the patch ?
> > 
> > hmm, iam not entirely happy with that patch
> > at least av_reduce() has to be added where its needed
> > and that needs to take care of cases where a non 0 value becomes
> > 0 through av_reduce()
> > maybe we could add a max_sar_component to AVCodec and use that to
> > reduce in ffmpeg.c ?
> > It feels correcter, i mean
> > "lets set 1000/513 and see what comes out, never knowing what really
> >  is stored ..."
> > vs.
> > "Ahh codec supports up to 255/255, lets reduce and store that"
> > 
> > PS: We already have seperate sar in AVStream and AVCodecContext so it
> > would not affect muxers
> 
> Well, if there is a way to have a max rational value for
> "sample_aspect_ratio" in AVOption (255/255),

i think AVOption cant do that yet


> I can implement per codec
> defaults and min/max using AVOptions * in AVCodec, what do you think ?

I thought simply adding the aspect parameter to ffmpeg.c so it isnt parsed
via AVOptions would be a simple solution ...

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

Dictatorship naturally arises out of democracy, and the most aggravated
form of tyranny and slavery out of the most extreme liberty. -- Plato
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