[MPlayer-users] Capture: video buffer full - dropping frame

[eyagerlist at chartermi.net]

On Fri, 8 Oct 2004, Heine Laursen wrote:

> Hi.
>
> I just tryed to capture a show with mencoder, but suddenliy at midways I
> see alot of these messages; video buffer full - dropping frame
> At end of capturing mencoder tells me that there are 331 frames dropped!
> I did'ent really touch the computer mutch at encoding. And I encoded
> useing nice -n -19
>
> I captured to at 80 GB SATA Harddisk, dedicated to capture!
>
> I used the following command to encode:
> nice -n -19 mencoder -endpos 01:40:00 -tv
> driver=v4l2:input=2:mjpeg:normid=0:decimation=1:adevice=/dev/dsp0:amode=1:fps=25
> -ovc lavc -lavcopts vcodec=huffyuv:vstrict=-1  -oac copy -o capture.avi
> tv://
>
> Are there any thing wrong with my mebcoder options?

First, you've set your capture card to use hardware MJPEG compression. 
Most video codecs use a raw uncompressed video stream on their input. 
Mplayer has to convert the MJPEG video stream back into a raw stream for 
use with other video codecs which is wasting CPU time.  If you don't 
intend on creating an AVI on-the-fly with an MJPEG encoded video stream, 
set the video capture card to output a raw uncompressed format instead.

Second, forget about using the huffyuv codec.  The huffyuv is a lossless 
compression.  Since you've already performed a lossy compression by 
setting your capture card to output an MJPEG video stream, using any 
lossless video codec is completely useless and entirely counterproductive. 
All it will do is create a larger file.

I don't have a capture card that does MJPEG compression, so I can't test 
this.  You should try to use "-ovc copy" instead of "-ovc lavc" which 
should (maybe), create an AVI with an MJPEG video stream.  For what you 
appear to be trying to accomplish leaving the MJPEG stream alone and 
copying it into the AVI is closest you are going to get to "lossless 
compression".

>
> What happend?
>
> What does "video buffer full - dropping frame" mean?

It means that your computer can't encode the video fast enough to keep up 
with the video capture card.  If it can't keep up, it will simply start 
throwing pieces of the video away to catch up.  When you play the video 
back you will notice many freezes in video and jerky motion.  Also huffyuv 
is very slow and possibly even broken.  Even on a very fast computer I
wouldn't expect it to work.



-- 
Eric