[Ffmpeg-devel] [PATCH] enable libswscale

Víctor Paesa wzrlpy
Fri Aug 25 01:04:46 CEST 2006

Hi Luca,

Luca wrote:
> On Wed, 2006-08-23 at 19:28 +0200, V?ctor Paesa wrote:
> [...]
>> Here is my attempt to convert vhook/null.c
> I had a quick look at it, and it seems to be ok (modulo the checks on
> sws_scale() return value).
> Only one question: is it really possible that the image format or
> dimensions dynamically change? (I see you added support for this
> possibility).

I really added that support because pix_fmt, width, height exist as
parameters to Process(), if they wouldn't potentially change every frame,
then passing them as parameters to Configure() should be enough.

Changing pix_fmt seems overkill, but regarding dimensions, hmm,
I can read your question in two ways:

a) It might be possible to find videos were dimensions change, I can think
of captured DTV broadcasts, they may change size from comercials to

b) Currently ffmpeg is not supporting dimensions changes, at least in this
quick test:

ffmpeg -f image2 -i logo%d.png -y logo%d.jpg

The test source PNGs have different sizes, but the resulting JPEGs are the
same size.

But I not sure if ffmpeg was designed to support it. That looks a design
Michael, could you please shed some light?

>> I don't understand well if sws_scale returns any specific value to
>> signal
>> errors, does it?
> I think swscale does not return errors - and sws_scale() never fails (in
> fact, I see that the return value of sws_scale() is never checked in
> mplayer's code), but in the "swscale emulation" code I return a negative
> value in case of error.

OK, then I will remove the checks for what sws_scale returns.


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