[Bug 781069] postproc: framerate should not be always duplicated

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=781069

--- Comment #20 from sreerenj <bsreerenj at gmail.com> ---
(In reply to Nicolas Dufresne (ndufresne) from comment #19)
> In gstreamer caps, the framerate field is always frames. So the parser
> helper gst_h264_video_calculate_framerate() returns a framerate (it will
> half the SPS framerate).
> 

So the parser produces fps which is the actual number of frames outputting from
the parser, it won't send a field in a buffer I guess.
Then we all are good, gstreamer-vaapi should double the framerate IMO.

> Though, if I understood correctly, for scalerbob technique, if you don't
> double the rate, it means we will likely scale up all top fields, or all
> bottom fields, dropping the other fields. Is that what MSDK VPP
> implementation do ? This would obviously remove shakyness.

I'm not sure what msdk internally do, but it provides two modes for BOB. Either
you can output half-framerate or double-framerate. It is up to the user to
chose what he/she wants.

What I am curious is, whether the driver always doubles the fps or not. Is it
only msdk plays in the middle to drop or keep frames?

We are dealing with two drivers here. msdk uses iHD and gst-vaapi uses i965.
It is worth to investigate whether one driver has a mode to set the number of
frames required for deinterlacing based on user-provided fps.

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