> From: "Andrew A. Chen" <achen-v4l-list@xxxxxxxxxxxxxx>
> Date: Fri, 05 Jan 2001 09:10:00 -0800
>
> How does that streamer command work for you at all, if you're losing
> frames? If you lose frames, the audio/video drop out of sync, which makes
> that file somewhat useless, no? I use this, and I constantly get pages and
> pages of 4-8 frames lost. I've even tried to increase the buffer size in
> the btt driver.
>
> streamer -r 29.97 -t 9000 -o /mnt/media/foo.avi -j 60 -f mjpeg -F stereo -R
> 8000
>
> I just end up with pages and pages of this:
> rate: video is 8 frames behind
> rate: video is 8 frames behind
> rate: video is 7 frames behind
> rate: video is 7 frames behind
I don't think that being 7 frames behind doesn't mean that you've lost
them - the message comes from grabber_sw_rate() in grab.c which looks
like:
if (frames-count > 3)
fprintf(stderr,"rate: video is %d frames
behind\n",frames-count);
return frames-count+1;
and that is called from grab-v4l.c
rc = grabber_sw_rate(&grab_start,grab_fps,grab_frames);
if (rc <= 0)
goto next_frame;
grab_frames++;
So you get the warning message if the return value is positive and the
skipping frames occurs if the return value is zero or negative. I
guess this is what the buffer is for.
I'm no expert, but it seems to work. The sound quality is pleasingly
good (I've a nicam chip in my bt878 card which seems to be operational).
> This is a celeron 600 with 128MB RAM on an Intel D815EEAL board, hooked up
> to a UDMA/100 40GB drive... Am I running low on cpu speed, memory size,
> drive speed, or something else? I really want to get this to work. The
> key for me is getting ~320x240 at 29.97fps... Thanks.
I'm getting 320x240 at the default 10 frames/second. The key to
reducing the warning messages you and I see was reducing the rate the
video was written to the drive, so I guess writing more compressed, like
MPEG (I have yet to check out the recommended mp1e) or getting SCSI
drives will help.
Anyway, I've been recording for about a day now and only seen the
"frames behind" message about once a half hour, and have only filled 1/6
of my disk...
> From: "Thomas Hargrove" <ciagon@xxxxxxxxxxxxxxx>
> Date: Sat, 6 Jan 2001 00:58:30 -0800
>
> I have been working on the exact same problem. So far, here is what has and
> has not worked:
>
> Not worked:
> bttv + streamer - bad a/v sync
> bttv + bttvgrab - filesize too big
> bttv + fame - no audio support
> bttv + bcast2k - it's quicktime
>
> Has worked:
> bttv + realproducer - great a/v sync. rock solid. .rm only
> dc10 + lavrec - also good a/v. Does hardware mjpeg. No tuner :(
>
> I have not yet tried AviFile, but I don't have my hopes up.
Well, I've found that the mjpeg option ot the AVI file helps a lot as it
reduces the rate stuff has to be written to disk.
> Although it is a pain in the ass to get good automated video capture
> working under Linux, it is worth the effort. I have a Linux box
> that has been doing about 5 x 30min real video captures a day for the
> last 5 months. (like 50 gigs of compressed video) There has not been a
> single hiccup and I have not lost a single capture. I tried to do the same
> on a windows box and could only get one or two captures off before
> I needed to reboot.
Great to hear your story - thanks.
Tony Robinson
--
http://www.softsound.com
