[icecast] MP3 decoding, fading and streaming at the same time

Tim Pozar pozar at lns.com
Thu May 10 07:26:50 PDT 2001



I did something like this for KKSF where they wanted to mix between
a wave file and a the over the air signal to insert different spot
in the outgoing MP3 stream.  I put two sound cards in a machine as
they are cheap (~$20) played the wave on one sound card and mixed
between them with other sound card.  I wrote a program that looked
at a line on the serial port and if it went high it would run
"mixer" to crank down the live station feed, play the wave file
and then run "mixer" to turn up the live audio again.  One would
either have a 30 or 60 second wave file to insert or a long cut
and wait for the line to toggle back to go back to the live audio.
The scheme works for those folks running into the AFTRA problem.

Drop me a note if you want details or code.

Tim

On Thu, May 10, 2001 at 07:44:37AM +0200, Alfredo E. Cotroneo wrote:
> Hi There,
> 
> I have just ported to Linux a program that I wrote years ago in Prolog 
> under DOS to automate our Shortwave radio station. Back in 1990 the 
> original program used ADPCM coded audio files and a special board. Now I 
> can use MP3 files and a Soundblaster compatible card ;-) under Linux, and 
> it runs from a console without any fancy interface. I absolutely need to 
> fade-in and fade-out audio, and now I use the mixer capability of the 
> SoundBlaster, so a simple MP3 file scheduler is not enough for me.
> 
> I am now trying to feed the output of this program (actually the output of 
> the Sound card) to an icecast server. The easiest way would be to have 
> another sound card and connect line-out (1st card) to line-in (2nd card) 
> and use liveice to feed icecast. Either use two sound cards on the same PC 
> (I did not mange yet) or even two Linux servers ;-))
> 
> I wonder if there is another easier way to do it without two soundcards. I 
> MUST have fade-in/fade-out capabilities, and I currently use the card mixer 
> to do that. I tried i.e. feeding Line-out and line-in of the same (duplex) 
> Soundcard, but looks like the opensound audio driver cannot be open 
> simultaneosly by two applications (liveice should only read, mpg123 should 
> only write to the sound driver).
> 
> Any idea or suggestion to avoid having two sound cards to do what I need to 
> do ?
> 
> Or how to fade in / fade out without using the card' mixer, while playing 
> i.e. using mpg123 ?
> 
> Thanks.
> 
> Alfredo
> 
> 
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-- 
  Snail: Tim Pozar / LNS / 1978 45th Ave / San Francisco CA 94116 / USA
               POTS: +1 415 665 3790  Radio: KC6GNJ / KAE6247
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                        - Andrew Jackson
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