[mythtv-users] Is 4MV actually working?

[zoiks2004-ivtv at yahoo.com]

I am interested in getting maximum compression without
losing too much video quality.  To that end, I tried
checking out the effects fo the 4MV encoding with the
mpeg2->mpeg4 transcoder.  (I believe my digital cable
box uses mpeg4 with 4mv, if I understand 4mv
correctly.  I occasionally see blocks of video moving
around and rotating on the screen when the cable
connection has a glitch.)

Anyhoo, I took a ~20s recording and made copies of it
in the /store directory.  I then re-imported them into
the database using myth.rebuilddatabase.pl script,
giving them names like Test1 and Test2.  I then
transcoded them using 600kbps (to make the video
obviously degraded, so I could see an effect).  I
transcoded with myth once with 4mv encoding and then
once without.

The two transcoded videos were slightly different in
size (~1%), and since I know they started with
identical video files, I know transcode tried to do
something different with them.

But, hard as I looked, I could not tell *any*
difference in video quality.  I paused and looked at
various paused frames (it was a short recording of
some baseball) and both videos seemed identical in
quality.

So the question is, should I have seen a difference in
video quality?  Is there a possibility that 4MV is not
working due to my ffmpeg compile or something like
that?  Is there a better way to tell if 4mv works?  Or
is my experience to be expected?

Thanks!