[FFmpeg-devel] [RFC] libavfilter-soc and variable-frame-size video streams

Erik Kaashoek erik
Sat Dec 13 17:27:12 CET 2008

If someone ever needs a real- life mpeg test recording with variable 
frame rate send me a mail.

Stefano Sabatini schreef:
> On date Saturday 2008-12-13 14:23:40 +0100, Michael Niedermayer encoded:
>> On Fri, Dec 12, 2008 at 04:54:26PM -0800, Jason Garrett-Glaser wrote:
>>>> But maybe I'm just confused and there is a far simpler solution, or
>>>> maybe we could just decide that supporting variable-frame-size video
>>>> streams is not worth that hassle.
>>> This sounds reasonable to me: thinking through what every filter would
>>> have to do to support such a thing, it sounds completely
>>> unmaintainable, especially for filters that act temporally: how will
>>> they deal with the fact that cached temporal data from previous frames
>>> (such as for temporal denoisers) is no longer the correct size
>>> matching the current frame?!
>>> Avisynth gets away just fine without variable frame size support: I
>>> have actually never seen such a thing as a feature request either.  I
>>> don't think libavfilter needs it either.
>> I think variable size is pretty much a requirement for libavfilter.
>> I dont remember exactly how/if this was discussed during lavfi development
>> but it surly is not ok to drop it. Also lack of support of it in Avisynth
>> is not an argument not to support it in lavfi.
>> About individual filters, variable size support is surely optional and
>> that way its no burden on a per filter level.
>> Filters that are "stateless" should be able to very easily support it,
>> the scale filter has to support it for the obvious reason to remove
>> size changes at the begin of a filter chain when that is wanted.
>> and temporal filters may or may not be able to easily support it, after
>> all they dont have to do much more than free their stuff and pretend its
>> the start of a stream.
> I'm thinking about something like avfilter_config_output_links(),
> which should work in a way very similar to avfilter_config_links, and
> maybe will share some code with it.
> It may work like this: when the request_frame callback of a filter
> recognize that the frame to output changed its size, it will call
> avfilter_config_output_links(), which will run all the config_props of
> the *input* pads of the following filters in the chain.
> Regards.

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