[FFmpeg-devel] [PATCH] mov: support for Quicktime CLEF/TAPT atoms

[Tim Nicholson]

On 03/07/12 15:50, Nicolas George wrote:
> Le sextidi 16 messidor, an CCXX, Tim Nicholson a écrit :
>> This sounds like the right approach. However where can you currently
>> define the pixel rectangle for which the DAR is calculated? For example
>> the setdar filter allows the DAR to be set and calculates the SAR on the
>> basis of the equation I quoted.
> 
> As far as I know, a SAR field is always part of a structure such as AVFrame,
> AVCodecContext, AVFilterLink, AVFilterBufferRefVideoProps, etc., and these
> structure always have a pair of width, height fields. These three fields
> work together.
>

So if there is only one pair of width, height fields, then the equation
will always have to hold true. It sounds like what is needed are two
pairs, one the actual frame size, the other the pixel rectangle for
which the DAR is relevant, which is roughly what quicktime provides. By
default these two pairs would be the same but could diverge if required,
allowing one pair to maintain the defined relationship while the other
was decoupled from this, but providing the necessary information as to
the actual pixel dimensions of the coded frame.

This is the kind of API change I was contemplating might be needed,
based upon my reading of past discourses.

-- 
Tim