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Unofficial VirtualDub Support Forums > Codec Discussion > H.264 And Virtualdub Hack -> What Does It Do?

Posted by: Barnister Feb 8 2011, 10:36 AM

Howdy,

I've noticed the Option VirtualDub Hack (http://i.imgur.com/XsCjp.png), I've always been using it, just because I thought it'd be good without ever reading up what it precisely does.

Now, the only thing I could find so far is:

QUOTE

The "VirtualDub Hack" option is highly recommended when using x264vfw with VirualDub (or VirtualDubMod). And it does NOT recommended with other encoding programs. It helps to overcome the limitation of VFW interface with its ideology of "one frame in, one frame out" when using B-frames or frame-base multithreading (or other techniques where frame buffering is needed).

I'm still a late-stage newb concerning video codecs and rendering. Can someone please explain to me, in detail preferably, a newb, what it precisely does?

Thank you in advance!

Posted by: phaeron Feb 13 2011, 10:42 PM

I haven't looked at the details, but I believe it allows the codec to see frames in both directions (forward and backward) when deciding how to compress one. The reason for it being a hack has to do with the VFW codec interface in Windows that everything is being funneled through.

Posted by: BugMaster Feb 14 2011, 06:22 PM

This is the main thing it do: http://x264vfw.svn.sourceforge.net/viewvc/x264vfw/trunk/codec.c?revision=30&view=markup#l1424

Posted by: i4004 Feb 14 2011, 06:54 PM

could we get the same in plain language?
for all of us non-programmers.

Posted by: stephanV Feb 14 2011, 07:07 PM

If I understand correctly it is doing the same thing as DivX and XviD, only without packed bitstream. It's sending delay frames which VirtualDub knows to remove.

Posted by: i4004 Feb 14 2011, 07:33 PM

is it a way encoder is fetching frames to encode, or a way one is packing frames to .avi?

Posted by: stephanV Feb 14 2011, 07:37 PM

The first.