Re: [gentoo-user] [OT] using ffmpeg for screen cast

[Stroller]

On 26 June 2011, at 19:54, Mick wrote:
>>> ...
>>> ffmpeg -f x11grab -s xga -r 25 -i :0.0 -aspect 4:3 /tmp/out.mpg
>>>
>>> but the result is rather blurred as you can see in the attached
>>> screenshot, when I play it with mplayer.
>> ...
>> Try passing "-sameq"
>
> WOW!  Exceptional improvement in a single stroke!  Thanks!  :)
>
> Why is it that ffmpeg degrades the quality with default settings?  What does
> it assume that the setting is? (sorry for the newbie Qs, but this area is
> until now outside my cognitive map! ;-)

I don't know about the "default" settings, but I would interpret the file extension of your original command as telling mplayer that "the destination file should be encoded as mpeg2". This is a pretty poor codec by today's standards.

I could well be wrong, though. Do you know what format the output file is?

IMO you're best encoding to h264 (in an mp4 container) for distribution, but I think it's possible the encoding load of that might affect your screencast. So you might wish to use sameq or the r210 or rawvideo codecs and then transcode to h264 (or WebM or whatever) afterwards.

> Now, I hope I'm not getting greedy, but how do I add voice recording to the
> above stanza?  Or do I have to record voice and then package it along with the
> video in a container as a separate step?

EXAMPLES                                                                        
   Video and Audio grabbing                                                     
       FFmpeg can grab video and audio from devices given that you specify the  
       input format and device.                                                 
                                                                                
               ffmpeg -f oss -i /dev/dsp -f video4linux2 -i /dev/video0 /tmp/out.mpg

       Note that you must activate the right video source and channel before    
       launching FFmpeg with any TV viewer such as xawtv                        
       (<http://linux.bytesex.org/xawtv/>) by Gerd Knorr. You also have to set  
       the audio recording levels correctly with a standard mixer. 

Audacity is widely used for simple audio editing.

Stroller.