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

[Baptiste Coudurier]

Hi Michael,

On 6/12/2009 8:12 AM, Michael Niedermayer wrote:
> 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

Well too bad. Want to improve it ? :)

>> 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 ...

Well I don't see any point adding max_sar_value to AVCodec when
AVOptions exists.

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
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