On Sat, Mar 22, 2003 at 10:51:56AM -0600, Dave Ladd wrote:
> In any case, I got much better results putting the timeshift buffer on 
> a tmpfs file system. The one issue I worry about with that solution is 
> how big I can make the buffer, though.

In my experience, one hour = 1 gb with default mp1e settings. I think
at least 10 minutes would be necessary for this to work. If you have a
spare 200mb of RAM, that would do it :)

> - audio mixing: I ended up changing the mp1e command line to specify a 
> non-existent dev file for the mixer device, which allowed me to set up 
> the mixer beforehand from the command line. If you think about it, 
> timeshifting actually simplifies the overall TV mixing problem quite a 
> bit. With timeshifting, you always have the "record side" of the mixer 
> set to record TV, and the "playback side" of the mixer set to play PCM 
> audio. For instance, in my case, I always want line-in muted (but 
> non-zero volume).

I haven't run into that because I use btaudio; but I agree that using
timeshifting works around most of the sound sync issues.

> - channel changing: I compiled Aubin's "chchan" app and was hoping that 
> calling it from Python would work. Unfortunately, it didn't seem to 
> work when /dev/video0 was in use. It works fine to initially set the 
> channel, but changing the tuned channel in mid-timeshift is not working.

I ended up writing a shell script to replace the chchan program using
mplayer (which we already have) I hope this isn't really dumb, but I
use this for recording as well:
---
echo q | mplayer -quiet -vo null \
-tv 
on:driver=v4l:device=/dev/video:input=0:norm=NTSC:channel=$1:chanlist=us-cable:width=640:height=480:outfmt=yuy2
 \
  > /dev/null 2>/dev/null
---
I just have mplayer tune in the channel with vo null/ ao null so it
doesn't put anything on the screen and then quit.

However, in regards to changing the channel "live" (i.e. without
closing /dev/video and re-opening) you need v4l2 to do that. v4l
simply can't change the channel without the device being closed.

> Rather than trying to extend mp1e to do channel-changing, does anybody 
> know how to run mencoder instead of mp1e for the encoding half? I had 
> initially tried encoding with mencoder, using the default recording 
> setup, but the player was unable to figure out what format the stream 
> was in. Futhermore, even if mencoder could write an MPEG stream to the 
> timeshift buffer, could it also run the slave interface and support 
> channel changing?

I don't think mencoder can do anything that mp1e can't do with a
wrapper around it; I can't even use mencoder myself because it's too
CPU demanding.  Plus, mencoder still doesn't support v4l2, which for
the sync fixes alone, is worth using.







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