[FFmpeg-devel] [PATCH] Export large crop values via AVCodecContext

[David Conrad]

On Jun 3, 2009, at 6:48 PM, Michael Niedermayer wrote:

> On Wed, Jun 03, 2009 at 06:43:33PM -0400, David Conrad wrote:
>> On Jun 3, 2009, at 11:34 AM, Michael Niedermayer wrote:
>> 
>>> On Thu, May 28, 2009 at 09:10:45PM -0400, David Conrad wrote:
>>>> Hi,
>>>> 
>>>> As far as I can tell, it's impractical to crop large values internally,
>>>> since buffers returned from decode_frame must have the same dimensions as
>>>> AVCodecContext, which also must be the coded dimensions (or up to 15 
>>>> less)
>>>> in order for get_buffer to allocate buffers of the needed size.
>>>> 
>>>> Thus, the only solution I see is to export these values and leave it to
>>>> individual applications that care about such offsets to deal with it
>>>> themselves.
>>> 
>>> I think these values can be exported through AVCodecContext.pan_scan
>> 
>> From my understanding of mpeg-2 (the only place AVPanScan is currently 
>> used), the area(s) in a AVPanScan are the more important areas in a frame 
>> that shouldn't be cropped e.g. when changing aspect ratio, while these 
>> cropping offsets aren't intended to be displayed ever.
> 
> My interpretation of mpeg2 is that AVPanScan is exactly the rectangle that
> is intended for display of a given aspect ratio.
> So i would guess that a 16:9 video could contain a single 4:3 panscan
> rectangle
> 
> 
>> 
>> Also, H.264 has separate pan-scan fields than what are exported here, 
>> relative to this cropping (D.2.3 Pan-scan rectangle SEI message semantics)
> 
> I know, thats why i hesitated with my reply
> but the crop values really are easier to use if they use the same API,
> the crop rectangle maybe should be somehow marked as overriding the
> main rectangle by default.

Seems I forgot about this.

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