[gst-devel] a stupid question

[David Schleef]

On Tue, Mar 18, 2003 at 05:34:52PM +0100, Thomas Vander Stichele wrote:
> Hey,
> 
> I'm picking up development again for an old gstreamer app I did two years 
> ago that I need to use again pretty soon.
> 
> The concept was pretty simple: the app is supposed to record bits of audio 
> coming in on the sound card, and each consecutive run of audio that 
> crosses a given threshold for a set amount of time should be recorded to 
> it's own file.
> 
> So the end result is a bunch of .wav files (or oggs, whatever) that each 
> hold a piece of audio as it was read by someone.
> 
> The most important thing to get right in this app is the fact that the app 
> should actually continuously pre-record to monitor the level, and when the 
> threshold is crossed, it should also store the previous 0.5 secs of audio, 
> so that the crossing of the threshold is stored as well, since that 
> typically also contains audio to keep.


What you describe is pretty close to one of my target applications.
I've been working toward it in the context of gst-sci, so some
of the elements have unfamiliar names.

The following script does what you are talking about, to
single-sample accuracy (it's important to me...).  This version
doesn't do pre- and post- triggering, but that was a simple
parameter to 'gate', IIRC.  The plplotsink thread is only for
monitoring purposes.

'comedisrc' is source for Comedi devices.
'envelope' converts an evenly-sampled data stream (like audio) into
  some approximation of its amplitude.  (Implemented as rectification
  and low-pass filtering.)
'trigger' converts an evenly-sampled data stream into a timestamp
  stream, which is just a sequence of sparse {$time,1} or {$time,0}
  points to indicate enabling or disabling a gate
'gate' chops up an input stream based on triggers received on the
  trigger_sink pad, optionally sending a NEW_MEDIA event when a
  new segment starts.

One of these days, I'll get the time to update gst-sci for 0.6.0,
and do a release.



dave...


#!/bin/sh

gst-launch $* \
  comedisrc rate=10000 ! \
  tee silent=1 \
  tee0.src%d\!sink { queue ! \
    envelope ! \
    decimate ! \
    framer chunk_size=1000 max_rate=20 ! \
    plplotsink marker=0.001,1.0 zero=true \
  } \
  tee0.src%d\!sink { queue ! \
    envelope ! \
    trigger set_level=1.0 reset_level=0.5 ! \
    queue \
  } src!gate0.trigger_sink \
  tee0.src%d\!sink { queue \
  } src!gate0.sink \
  { \
    gate ! \
    filesink location=x%d \
  } \
  2>&1