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

[Janez Pers]

Reimar Döffinger wrote:

> 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.

Thanks for these hints, I guess this brings me much closer to the
motion data.

>> 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...

I have observed the motion vectors that Axis 207 produces, and they are
well, extremely good, almost stunning.  (disclaimer: I am not affiliated
with Axis, otherwise I would not bother to decoding the stuff camera
itself produces, obviously :)

I had similar observations like you with other encoders, even with many
software motion estimation schemes available through mencoder.

Janez.