Editing Sound on the Fly

Tue Jul 12 18:07:50 UTC 2016

Janina Sajka wrote:
> Am I missing the obvious? Or is the obvious not stated in the
> requirements?
> 
> What i mean is that by the time you hear something interesting, it's too
> late to start recording. That part of the stream has passed.

> In other words, you need to copy from a stream that's buffered by some
> amount of time. What amount of time is whatever you judge to be a
> sufficient interval of time in order to judge that something is
> interesting. I believe radio stations typically use a 7 second delay
> where they're taking live calls on air -- in order to edit out people
> trying to say nasties on air. That kind of fifo buffer for the stream
> should work here, too.

There exists a recording utility for that, a plugin that runs under JACK. 

http://plugin.org.uk/timemachine/

> Of course, you have a similar problem at the end of "interesting
> segment" You need to make certain you don't cut off the copy too soon.
> So, either you brute force by waiting a compensatory of additional time,
> or have some way to switch to monitoring the buffered recording in order
> to know when to stop copying.
> 
> hth
> 
> Janina
> 
> Willem van der Walt writes:
> > Hi,
> > Hart mentioned my program called dae (short for digital audio editor), so I
> > will try and explain to what extent it might do Martin's job.
> > If you convert  your 8-bit raw audio into a wav file using sox or similar,
> > you can use dae on it.
> > Dae will start playing the file when it is loaded and, while playing, one
> > can press a button, f5, to mark the start of a block. This will be when you
> > reach the audio that is interesting.
> > One can then press f6 when the interesting part is passed.  That block can
> > then be written out to a separate file using f8, which allow you to specify
> > a file name for the block.
> > Alternatively, while the file is playing, one can press p which marks a
> > position in the file. Each time you want to have a track boundary, you press
> > p.  once you are done, you can press S to split up the file into the tracks
> > defined by the marked positions.
> > 
> > This might almost do what you want, but maybe not quite.
> > Dae uses ecasound for the heavy lifting and is written in python.
> > HTH, Willem
> > 
> > 
> > On Mon, 11 Jul 2016, Joel Roth wrote:
> > 
> > > Hi Martin,
> > > 
> > > > From what you write, I think you want to extract interesting
> > > parts of an audio file to another audio file, although you
> > > could mean extracting parts of an audio *stream* to a file.
> > > 
> > > I looked at ecasound. I came up with a plan, but I think it
> > > won't work because I don't see an easy way to append output to an
> > > existing file.
> > > 
> > > Nama (which uses ecasound) is another possibility. Nama can
> > > extract parts of an audio file, and has some special
> > > features for that purpose. Basically, you drop marks in
> > > pairs, create a sequence using the content between the
> > > marks, and then export the desired audio via mixdown. Right
> > > now you have to specify the list of marks to use, but we
> > > might find ways to simplify that when dealing with large
> > > numbers of marks.
> > > 
> > > regards,
> > > 
> > > Joel
> > > 
> > > Martin McCormick wrote:
> > > > 	I am always looking for the easiest way to do things but
> > > > am also aware of that quotation which goes "The lazy man works
> > > > the hardest."
> > > > 
> > > > 	I want to play a file which is usually 8-bit audio at
> > > > a sampling rate of 8000 samples per second, sometimes called raw
> > > > 8-bit audio. If I hear something worth saving, I would like to
> > > > copy that part of the stream to a new file and then stop the copy
> > > > when the good stuff has passed, just like dubbing from one tape
> > > > recorder to another.
> > > > 
> > > > 	I just installed ecasound as it should be able to
> > > > accomplish this task but the question is will mplayer also do this?
> > > 
> > > > 	The idea is one listens, hears something interesting to
> > > > save, starts the recording at the right time and then stops it
> > > > after the gem has been saved while the master continues to play.
> > > > If a new treasure comes by, start recording again and save that
> > > > in the same new file or maybe a series of files depending upon
> > > > what one wants.
> > > > 
> > > > 	Thanks for any suggestions. This audio is radio traffic
> > > > so it doesn't need to be high fidelity. One usually wants the
> > > > most audio crammed in to the least space.
> > > > 
> > > > Thanks for all good ideas.
> > > > 
> > > > Martin WB5AGZ
> > > > 
> > > > _______________________________________________
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> > > 
> > > -- 
> > > Joel Roth
> > > 
> > > 
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> -- 
> 
> Janina Sajka,	Phone:	+1.443.300.2200
> 			sip:janina at asterisk.rednote.net
> 		Email:	janina at rednote.net
> 
> Linux Foundation Fellow
> Executive Chair, Accessibility Workgroup:	http://a11y.org
> 
> The World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI)
> Chair, Accessible Platform Architectures	http://www.w3.org/wai/apa
> 
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-- 
Joel Roth