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--></style><title>Re: [Asterisk-Dev] Re: MS-ADPCM in
format_wav?</title></head><body>
<blockquote type="cite" cite>On Wed, 2005-02-02 at 15:47 +0000, Tony
Mountifield wrote:<br>
> In article <1107359089.2799.18.camel@critch>,<br>
> Steven Critchfield <critch@basesys.com> wrote:<br>
> > On Wed, 2005-02-02 at 11:02 +0000, Tony Mountifield
wrote:<br>
> > > Does anyone know if there has been any work done on
enhancing format_wav<br>
> > > to support MS-ADPCM format (fmt codec type 2)?<br>
> > ><br>
> > > If not, I may consider having a go myself, but I don't
want to re-invent<br>
> > > the wheel unnecessarily.<br>
> ><br>
> > You wouldn't modify format_wav under the current method. You
can copy it<br>
> > to format_wav2 to mimic the way GSM wav files are handled
by<br>
> > format_wav49. Then you only need to modify the seek
function, and the<br>
> > header creation/update. After that, you just need to make
sure the codec<br>
> > is set to adpcm so your incoming frames are already in the
right format.<br>
><br>
> OK, thanks, I'll have a look at that. At the moment, I'm more
interested<br>
> in being able to play adpcm files than record them. Rather than
relying<br>
> on a matching codec, I was thinking more of having format_wav2
decode the<br>
> ADPCM into SLIN or something, like format_mp3 does.<br>
><br>
> And having each format in a separate module looks like it
requires each<br>
> format to have a different file extension, rather than looking at
the<br>
> fmt chunk in the file to determine the format. Is that
correct?<br>
><br>
> I'll take a look at format_adpcm too. Thanks to you and bkw for
the pointers.<br>
<br>
Ideally, if asterisk doesn't support the codec, you should look
into<br>
making the codec then. Putting audio encoding at the format level
isn't<br>
a real good idea.<br>
<br>
Now as for combining the wav functions into one simple format_wav,
that<br>
wouldn't be too bad. Of course you would still have to signify to<br>
asterisk what codec you wanted the file to be recorded in when you
said<br>
wav. The only thing that is different between the 2 currently
supported<br>
wav formats is the header functions and a few assumptions with how
to<br>
deal with blocks of audio for the codec.<br>
<br>
For instance, in format_wav_gsm, you read a 65 byte block and send it
to<br>
the on it's way. you can not use anything smaller than 65 bytes, and
you<br>
have to be on the proper boundaries too. But in format_wav, you
just<br>
have to be on the right 2 byte boundary to send the slinear bytes to
the<br>
codec.<br>
<br>
I'm assuming adpcm and MS-adpcm is similar. <br>
--</blockquote>
<blockquote type="cite" cite>Steven Critchfield
<critch@basesys.com></blockquote>
<blockquote type="cite" cite><br></blockquote>
<div><br></div>
<div><br></div>
<div>I'll throw in a couple of comments here. A good starting point to
understand the Microsoft-adpcm file format, is to read an Apple tech
note http://developer.apple.com/technotes/tn/tn1081.html that
describes the differences between IMA-ADPCM and MS-ADPCM, note the
real issue is how the data is stored on disk. RAW ADPCM samples (for
example if you put a voice capable modem into voice mode (see the
V.253 Modem AT Command set) then asterisk's adpcm codec will handle
it. However it's when windows software "writes these adpcm
samples to a wav file, is where the issue is..</div>
<div><br></div>
<div>The original question (correct me if i am wrong Steven) is how to
take a windows .wav file that contains adpcm audio samples that
are created under MS Windows and "play" them to a caller via
asterisk. The Apple tech note is a great starting point on describing
the issues for parsing the data.</div>
<div><br></div>
<div>Another good open source code base that I have used to read and
"play" a windows .wav file over a modem (i.e an answering
machine) is the vgetty/voice subproject that's part of mgetty.
There is code in vgetty that parses the MSADPCM wav file and creates a
.RMD file (which is a RAW ADPCM file) that you just write to the phone
line.</div>
<div><br></div>
<div>Do a search for "<font face="Courier" size="+2"
color="#000000"><b>pvf tools</b></font>" to see some of the
different formats supported by the vgetty project.</div>
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