[PD] [OT]: Screencasts on Linux Debian with Jack and ffmpeg - [WAS] Re: data structure setsize allocation

Lorenzo Sutton lorenzofsutton at gmail.com
Sun Nov 16 23:16:37 CET 2014

On 12/11/14 04:06, Jonathan Wilkes via Pd-list wrote:
> Sure... what do people use in Debian/Ubuntu to do screencast + audio?

With Jack I use someting like this:

ffmpeg -f jack -ac 2 -i ffmpeg -f x11grab -r 25 -s 1366x768 \
-i :0.0 -acodec pcm_s16le -threads 0 output.mkv

Notice that:

- ffmpeg in my case is the 'original' one compiled by hand. 
Unfortunately debian now seems to only package avconv and that has 
always crashed on me with jack as audio input. However ffmpeg is 
relatively easy to compile on debian following this guide:


- You should play with the -s and -i parameters to suit your needs.

- Pulseaudio will be automatically suspended when you run jack (I was 
forced to install it to use skype with, alas, I'm forced to use for work).

- Clearly when screen-casting it'll be difficult to get Chuck Norris low 
latencies without some xruns.

- The output with that ffmpeg command will be a very good quality mkv 
video however it will also be very (very!) big and you'll have to factor 
in the extra time for re-compressing (it's possible to encode on the fly 
-but I prefer to have a good quality 'original')
For encoding I've had rather nice results with using webem, for example 

ffmpeg -y -i "$INFILE" -threads 8 -f webm -vcodec libvpx -g 120 \
-level 216 -profile 0 -qmax 42 -qmin 10 -rc_buf_aggressivity 0.95 \
-vb 2M -acodec libvorbis -aq 90 -ac 2 $OUTFILE

Hope this helps.

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