[MPlayer-dev-eng] New filter vf_ivtc, smart dropping of every 5th frame

[Johannes Guenther]

D Richard Felker III wrote:
> On Sun, Feb 16, 2003 at 01:41:27PM +0100, Arpi wrote:
>> isn't -vop dint the same? afair it was written for the same purpose.
> AFAIK, -vop dint does not work at all. I've never been able to succeed
> in getting it to drop frames.

As described is the man page -vop dint wants to skip interlaced frames,
whereas -vop ivtc wants to skip duplicate frames (and skips only one out
of five).
After your hint I experimented with dint and had a look to its source
code - it is not useful for this purpose.

>>why do you need 6 frames for detecting duplicated frame?
>>keep only the previous one (IMGTYPE_IP) and comtare teh current one with
>>the previous, if the same, drop it.
> Agree!

I think using 6 frames is more reliable.
You can know for sure that the frame which was inserted is among this 6
(last) frames. Thus you choose to drop that frame that is the most
similar one. (Actually it is not that simple: for speed reasons not every
pixel is compared; so if the filter detects a second frame which seems
to be also similar to another frame, a second pass with comparing more
pixels is performed.)

Using only the (difference to the) last frame may lead to false
decisions. To decide whether to drop the frame in progress or not you
would need a threshold for the difference since the duplicated frame will
not be 100% the same (compression artefacts, etc.). But frames in dark
scenes with little motion will also fall under this threshold. With some
heuristics (drop only one frames out of five) you can avoid some of
this mistakes, but not all.

Greets,
	Johannes
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