[FFmpeg-devel] [PATCH] libavfilter-soc: Make overlay handle still images

[Michael Niedermayer]

On Thu, May 07, 2009 at 10:45:53PM +0300, Martin Storsj? wrote:
> Hi Vitor,
> 
> On Wed, 6 May 2009, Vitor Sessak wrote:
> 
> > Just a question: how are you testing those changes?
> 
> I'm testing it with the following command line:
> 
> ffplay in.mov -vfilters "movie=0:png:overlay.png, scale=0:0 [over1], [in] [over1] overlay=10:10 [out]"
> 
> and similarly with ffmpeg.
> 
> 

> > > +        oldpts = over->pics[idx][1]->pts;
> > >          if(avfilter_request_frame(link->src->inputs[idx]))
> > >              return -1;
> > > +        if(over->pics[idx][1]->pts == oldpts) {
> > > +            /* no new pts, we're probably at eof, pull a frame
> > > +               from the other queue to keep it moving */
> > 
> > The correct way to know if the video is over is to check if request_frame()
> > returned -1.
> 
> That was my initial guess, too, but the movie source filter provides the 
> last frame repeatedly instead of returning -1.

I think repeatly providing a frame with the same PTS ad infinitum is not
correct


> 
> This can easily be fixed by the first attached patch. (It contains checks 
> both before and after movie_get_frame, to avoid unnecessary calls to the 
> underlying layers after reaching eof.)
> 
> 
> When this is applied, the eof handling in the overlay filter can be fixed 
> in a few other ways, named -overlay-eof2 and 4.
> 
> The first one, -eof2, alters the frame pulling logic only slightly. The 
> request_frame function returns -1 when unable to pull frames from both 
> streams. Since a stream may contain only one frame, it requires the image 
> copying to try to check over->pics[idx][1] if over->pics[idx][0] is null.
> 
> The second way of solving it, -eof4, moves the last frame from 
> over->pics[idx][1] into over->pics[idx][0] by a 
> start_frame(link->src->inputs[idx], NULL) if there still is a frame in 
> over->pics[idx][1]. This way, all input frames should be output too. (In 
> the original overlay filter logic, the last input frame wouldn't be 
> output.)
> 
> Do these look sensible?

returning -1 is not good, it should be AVERROR_EOF and this must be
documented in the header.

also poll_frame() likely should similarly return AVERROR_EOF


[...]

>          if(avfilter_request_frame(link->src->inputs[idx]))
> -            return -1;
> +            if(avfilter_request_frame(link->src->inputs[!idx]))
> +                return -1;
>  

cosmetics

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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