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List:       mjpeg-users
Subject:    [Mjpeg-users]  Lavrec records blank
From:       "Ronald S. Bultje" <rbultje () ronald ! bitfreak ! net>
Date:       2007-05-01 18:44:12
Message-ID: 5D6B0110-A35D-4B6A-A61E-02D5C68F590B () ronald ! bitfreak ! net
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Hi,

On April 24, jankom@aahawk.com wrote:
> Trying to record from analog video camera playback with cheap bt878
> capture card, kernel 2.6.20 (Fedora-3) using lavrec.
>
> xawtv works fine, however, when start recording with lavrec xawtv  
> screen
> goes blue and remains blue even after stopping lavrec. Image can be
> restored in xawtv if I change input from composite1 to something  
> else and
> back to composite1. The recorded movie is blue screen either with  
> glav or
> with Mplayer. The same thing happens if I don't use xawtv, just record
> with lavrec.
[..]
> There are no error messages, recording seems progressing well.  
> There is a
> warning about "negative priority" and "Pthread" when lavrec starts. I
> googled it but could not find remedy for this.

So let's do this issue by issue. Threading is unrelated, this just  
sets process priority. Only root can do this, so running lavrec as  
user will cause such warnings. They're harmless for the issue that  
you're describing.

> While I'm not a linux expert I begin to understand how it works. I  
> suspect
> an input problem. xawtv hwscan shows /dev/video0 while Ronald Bultje's
> lavrec man indicates LAV_VIDEO_DEV /dev/video. So I tried to export
> LAV_VIDEO_DEV=/dev/video0 to no avail. I also tried "alias video  
> video0"
> in modprobe.conf, again, without success.

I think it picks up the video device just fine, given the response in  
xawtv (and the fact that it doesn't error out). I wouldn't worry  
about this.

> Here is the command to start lavrec (no audio as a stepwise debugging
> method):
>
> lavrec --software-encoding -a 0 -f a -g 352x288 -i n test.avi
>
> The recorded file size seems normal, but content is either hidden or
> content is blank.

Right, so no input. Have you tried -i n:0? It should do the same, but  
just in case. What input on the bt8x8 card are you capturing from?  
Tuner? composite? S-video?

> If I record with xawtv streamer I do get a video:
>
> streamer -t 0:10 -f jpeg -r 23.976 -s 352x288 -o video.avi
>
> video.avi plays with mplayer. On the otherhand, if I try lavplay  
> video.avi
> I get this:
>
> lavplay1.6.2
> lavtools version 1.6.2
> **ERROR: [lavplay] File video.avi has 23.976212 frames/sec, chose norm
> with +[np] param
>
> Now I don't underfstand this last one.

lavplay +n file.avi

Ronald


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