[FFmpeg-soc] Libavfilter RFC: problem with ffmpeg.c/ffplay.c integration

[Michael Niedermayer]

On Fri, Feb 01, 2008 at 10:18:27PM +0100, Vitor Sessak wrote:
> Hi
>
> Michael Niedermayer wrote:
>> On Wed, Jan 02, 2008 at 10:00:26AM -0500, Bobby Bingham wrote:
>>> On Wed, 02 Jan 2008 12:49:24 +0100
>>> Vitor Sessak <vitor1001 at gmail.com> wrote:
>>>
>>>> Hi all,
>>>>
>>>> I've spotted a problem with the ffmpeg.c integration using the command
>>>>
>>>> ffmpeg -vfilters fps=1 -i input.avi output.avi
>>>>
>
> [...]
>
>>>>
>>>> What is your opinion on that?
>>> I'll take a closer look at this tonight, but I think solution 3 sounds
>>> reasonable.
>> As nothing has been commited yet to solve this IIRC ...
>> what about
>>     /**
>>      * Frame poll callback.  This returns the number of immedeately 
>> available
>>      * frames. That is if it returns 1 or larger than the next 
>> request_frame()
>>      * is guranteed to return one frame (with no delay)
>>      *
>>      * Output video pads only.
>>      */
>>     int (*poll_frame)(AVFilterLink *link);
>> with that we could just check each output stream (there could be more than 
>> 1)
>> if a frame could be output. And if yes run a request_frame() on that. If 
>> no
>> stream has a >0 return for poll_frame() than another input packet could be
>> demuxed and decoded (from a file which caused a poll()==0) and send it to 
>> one
>> of the input vf_filo
>> poll_frame() could have a trivial default implementation which just polls
>> its input filters and returns that, this would be sufficient for 90% of
>> filters.
>
> Something like the following?

[...]
> +static int link_in_poll_frame(AVFilterLink *link)
> +{
> +    AVFilterLink *link2 = get_extern_input_link(link);
> +    if(!link2)
> +        return -1;
> +    return avfilter_poll_frame(link2);
> +}
> +
>  static int link_in_config_props(AVFilterLink *link)
>  {
>      AVFilterLink *link2 = get_extern_input_link(link);
> @@ -236,6 +245,15 @@
>      return -1;
>  }
>  
> +static int graph_out_poll_frame(AVFilterLink *link)
> +{
> +    AVFilterLink *link2 = get_intern_output_link(link);
> +
> +    if(link2)
> +        return avfilter_poll_frame(link2);
> +    return -1;
> +}

these 2 are inconsistant, with the retuen -1 and avfilter_poll_frame() order


[...]
> +static int poll_frame(AVFilterLink *link)
> +{
> +    FPSContext *fps = link->src->priv;
> +
> +    if (fps->has_frame)
> +        return 1;
> +
> +    if(avfilter_poll_frame(link->src->inputs[0]) &&
> +       avfilter_request_frame(link->src->inputs[0])) {
> +        fps->videoend = 1;
> +        return 1;
> +    }
> +
> +    fps->has_frame = !!(fps->pic && fps->pic->pts >= fps->pts);
> +    return fps->has_frame;
> +}

This should output values larger than 1 if its known that more can be
output from the available frame.


> +
>  static void end_frame(AVFilterLink *link)
>  {
>  }
> @@ -71,14 +90,17 @@
>  {
>      FPSContext *fps = link->src->priv;
>  
> -    while(!fps->pic || fps->pic->pts < fps->pts)
> -        if(avfilter_request_frame(link->src->inputs[0]))
> -            return -1;
> +    if (fps->videoend)
> +        return -1;
>  
> +    fps->has_frame=0;
>      avfilter_start_frame(link, avfilter_ref_pic(fps->pic, ~AV_PERM_WRITE));
>      avfilter_draw_slice (link, 0, fps->pic->h);
>      avfilter_end_frame  (link);
>  
> +    avfilter_unref_pic(fps->pic);
> +    fps->pic = NULL;
> +
>      fps->pts += fps->timebase;
>  
>      return 0;

This does not look like it would work if poll_frame() isnt used.
I did not intent to make poll_frame() mandatory to be used, but rather
an option for cases like ffmpeg.c.
That is pure use of request_frame() is fine as long as your inputs are
guranteed to be able to handle it until EOF.
I think the extra complexity for supporting both cases is quite small

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

it is not once nor twice but times without number that the same ideas make
their appearance in the world. -- Aristotle
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