[MPlayer-users] extracting motion vectors from MPEG4 stream/file

[Reimar Döffinger]

Hello,
On Fri, Feb 15, 2008 at 12:06:33PM +0100, Janez Pers wrote:
> - (most important) - is it a way to do it in a processing
> inexpensive way (my solution above requires essentially that
> the whole stream is decoded, played and motion vectors are
> drawn in addition to ordinary decoding) which is severe
> overkill, since I only need small amount of data which is
> essentially available in the stream itself, right? Which
> parts of the mplayer/ffmpeg pipeline could be relatively
> painlessly disabled so the actual IDCT and other cpu intensive
> stuff does not happen?

Have a look at the FF_DEBUG_MV define for avctx->debug and motion_val
array in AVFrame.
Also the skipidct and other skip options.

> final explanation of what I am trying to do: get Axis 207 camera
> to obtain motion vectors from its own MPEG4 stream. It has ARM
> processor (~ 200 MIPS), the mpeg4 encoding is done in hardware,
> if I understand correctly.

The motion vectors in standard cheap hardware encoders are usually not much
related to any actual motion...
Just try vismv on some DVDs, you'll surely find quite a few where even
during a smooth pan to one direction half of them point in the other
direction...

Greetings,
Reimar Döffinger