[FFmpeg-devel,PATCHv3] avfilter/vf_framerate: always request input if no output is provided in request_frame

Fixes ticket #6285.

Signed-off-by: Marton Balint <cus@passwd.hu>
---
 libavfilter/vf_framerate.c | 42 ++++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 16 deletions(-)

On Sat, 8 Apr 2017, Marton Balint wrote:

> Fixes ticket #6285.
>
> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
> libavfilter/vf_framerate.c | 42 ++++++++++++++++++++++++++----------------
> 1 file changed, 26 insertions(+), 16 deletions(-)

Applied this as well.

> @@ -695,7 +689,23 @@ static int request_frame(AVFilterLink *outlink)
>     }
>
>     set_work_frame_pts(ctx);
> -    return process_work_frame(ctx, 0);
> +    ret = process_work_frame(ctx, 0);
> +    if (ret < 0)
> +        return ret;
> +    if (ret)
> +        return ff_filter_frame(ctx->outputs[0], s->work);
> +
> +request:
> +    ff_dlog(ctx, "request_frame() call source's request_frame()\n");
> +    ret = ff_request_frame(ctx->inputs[0]);
> +    if (ret < 0 && (ret != AVERROR_EOF)) {
> +        ff_dlog(ctx, "request_frame() source's request_frame() returned error:%d\n", ret);
> +        return ret;
> +    } else if (ret == AVERROR_EOF) {
> +        s->flush = 1;
> +    }
> +    ff_dlog(ctx, "request_frame() source's request_frame() returned:%d\n", ret);
> +    return 0;
> }

Note that the above code which I moved returns 0 if ff_request_frame 
returns AVERROR_EOF. As far as I see, this can only happen a few times, 
not infinitely, so I am not sure if this is an error or not, so I kept is 
as it was before.

Regards,
Marton

Le tridi 23 germinal, an CCXXV, Marton Balint a écrit :
> Note that the above code which I moved returns 0 if ff_request_frame returns
> AVERROR_EOF. As far as I see, this can only happen a few times, not
> infinitely, so I am not sure if this is an error or not, so I kept is as it
> was before.

There are exactly three acceptable behaviours for request_frame() and
all the functions it calls:

* it pushes a frame and returns 0;

* it issues a ff_request_frame() on the input and returns 0;

* it returns EOF or an error.

If the "few times" correspond to frames pushed, then it is ok.
Otherwise, it is not. lavfi will not activate filters saying "hey, you
told me last time you had nothing to do, but just in case I am taking
news". A filter should never do nothing.

Regards,

On Wed, 12 Apr 2017, Nicolas George wrote:

> Le tridi 23 germinal, an CCXXV, Marton Balint a écrit :
>> Note that the above code which I moved returns 0 if ff_request_frame returns
>> AVERROR_EOF. As far as I see, this can only happen a few times, not
>> infinitely, so I am not sure if this is an error or not, so I kept is as it
>> was before.
>
> There are exactly three acceptable behaviours for request_frame() and
> all the functions it calls:
>
> * it pushes a frame and returns 0;
>
> * it issues a ff_request_frame() on the input and returns 0;
>
> * it returns EOF or an error.
>
> If the "few times" correspond to frames pushed, then it is ok.
> Otherwise, it is not. lavfi will not activate filters saying "hey, you
> told me last time you had nothing to do, but just in case I am taking
> news". A filter should never do nothing.

Well, then I guess the doc/filtering_design.txt is outdated, because
it uses term "making progress towards producing a frame" when returning 0

There is also an example code snippet there:

         if (frames_queued) {
             push_one_frame();
             return 0;
         }
         input = input_where_a_frame_is_most_needed();
         ret = ff_request_frame(input);
         if (ret == AVERROR_EOF) {
             process_eof_on_input();
         } else if (ret < 0) {
             return ret;
         }
         return 0;

Am I getting this right, process_eof_on_input() should be extended to

process_eof_on_input();
if (!frames_queued)
     return AVERROR_EOF;
push_one_frame();

Regards,
Marton