[gst-devel] framerate and deinterlace2

Sebastian Dröge sebastian.droege at collabora.co.uk
Sat Dec 6 10:29:05 CET 2008

Am Freitag, den 05.12.2008, 21:43 +0100 schrieb Julien Isorce:
> Hi,
> I would like to know why deinterlace2 changes the framerate ? (see
> gst_deinterlace2_getcaps then gst_fraction_double).
> I do not a lot about the deinterlacing methods. But in an interlacing
> video flux, an odd frame follows an even frame. Using a frame and its
> previous frame, the result is one deinterlaced frame.
> And so why N interlaced frames you got N-1 deinterlaced frames. 
> Finally there is no reason to change the framerate.
> I am sure I am wrong or missing something important but something I
> got a framerate about 50/1 in the deinterlace2 ouput while the input
> framerate is 25/1.
> Could someone explain this behaviour ?
> Maybe it depends  on the method used (deinterlace2 "method" property).

It doesn't depend on the deinterlacing method (but some produce a
jumping picture if outputting the doubled framerate).

The fields property can be used for this, if it's set to all you will
get the doubled framerate, top/bottom will only output the interpolated
top or bottom field.

Let's assume you have a interlaced video (with both fields weaved into
one frame) with 30fps. Taking every even line corresponds to one field,
every odd line corresponds to the other field then. Now these two fields
don't have the exact same timestamp but the second field is 1/2 frame
after the first one, i.e. 1/60 second in our example. The fields=all
deinterlacing will now output a frame every 1/60 seconds, where every
frame is created from the corresponding field and the missing lines are
interpolated by some method (which you can choose with the method
property). This method could of course be to simply take the missing
lines from the previous or following field but there are also some more
complex methods ;)
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