[MPlayer-users] MEncoder: Low frame rate on capture from tv

[Anurag Mehra]

Hello everyone

This mail is to seek help for a very unexpected problem. When I capture
from a v4l source like tv tuner the frame rate is really low:

at 704x576 it is 4 fps
at 352x288 it is 8 fps
at 160x120 it is 25 fps

The command line I use is:

mencoder -tv
on:driver=v4l:width=352:height=288:input=2:norm=PAL:channel=europe-west
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=900 -oac mp3lame -lameopts
cbr:br=128 -vop pp=lb -o mtest.avi
(load shoots above 2.0)

The problem persists even when I use -ovc rawrgb and -oac pcm so the
problem has probably very liitle to do with compression but has to do
with capture itself.

I think that the hardware that I have is powerful enough to capture and
encode in real time. The hardware/software is:

Intel 850 motherboard, 512MB RDRAM, P4 2 GHz CPU and 80 GB IDE (7200 rpm)
hard disk, MATROX marvel G400 with tv tuner, running redhat 8.0.

Interestingly, when I just watch tv using the command:
mplayer -tv
on:driver=v4l:width=352:height=288:input=2:norm=PAL:channel=europe-west
-vo xv

the motion is very jerky and blocky, just the way the captured avi file
looks. The CPU usage hovers around 70 to 80% and the machine load crosses
2.0!

In contrast xawtv work very well and mjpegtools based capture also
works flawlessly (dma is enabled, so write speeds is not a problem). Main
actor (macap) also works fine.

However, transcode, avicap also capture just like mencoder: giving very
low frame rates and consequently very jerky video. avicap shows lots of
dropped frames, perhaps 70% or more.

Mplayer, in general, seems to work quite well on all the video output
options (x11, xv, xmga etc) when playing all kinds of files and dvds.

Have checked everything that I came across but am unable to figure out
what can be wrong. I thought that with the hardware in question I could
easily capture at 25 fps and encode to divx4 or xvid at a resolution of
(greater than?) 352x288 in real time.

Would be very grateful for tips and experiences that others may have had
in this regard.

Thanks

Anurag
_____________________________________________________________________
              Dr. Anurag Mehra, Professor
Department of Chemical Engineering, Indian Institute of Technology,
               Powai, BOMBAY 400 076, INDIA
_____________________________________________________________________