[asterisk-users] file command with alaw file

[Steve Murphy]

Quyps--

I've noticed in general that the ulaw, alaw, gsm, slin files used and
generated by
asterisk do not have headers (the RIFF stuff), and asterisk is not expecting
them. in general they
will louse up Asterisk's ability to play the sound. They are just raw data
and the extension
on the file name (.gsm, or .ulaw, etc) is the only clue to the file
format/contents.

In general, if you need a sound file of your own making in a certain format,
you can convert
to most of the formats using sox in linux, but really, the best thing to do
is record the source
sound file in cd-quality sound WAV format, in 44 khz sampling rate, or
higher, and then
use sox to convert to 8khz format. Asterisk can do some of this via the file
convert CLI
command, ( on the asterisk cli, type "help file convert"). You'd have to
judge for yourself
if "file convert tt-weasels.gsm tt-weasels.ulaw" which would convert the
8khz gsm format to
8 khz ulaw, or "sox -v 0.7 tt-weasels.44khz.wav -r 8000 -c 1 -t sw
tt-weasels.raw;"
"sox -r 8000 -c 1 -t sw tt-weasels.raw -t ul tt-weasels.ulaw"  which is the
way the Asterisk
sounds are produced from the the cd-quality sounds. They would seem a bit
equivalent.

I wonder if just "sox -v 0.7 tt-weasels.44khz.wav -r 8000 -c 1 -t ul
tt-weasels.ulaw" would
sound any better... you audio engineers out there may have an opinion.

I've personally noted that not all linux distributions provide the same
version of sox;
some distribute sox with an absolute minimum of sound formats built-in. You
may have
to go out and find all the libraries and roll your own sox.

murf





On Wed, May 19, 2010 at 10:34 PM, Pham Quy <quyps at vega.com.vn> wrote:

> On Mon, 2010-05-17 at 17:49 +0700, Pham Quy wrote:
> > On Mon, 2010-05-17 at 13:06 +0700, Pham Quy wrote:
> > > hi all,
> > >
> > > I install Asterisk 1.6 on Centos 5.2 (kernel 2.6.18-92.el5 #1 SMP Tue
> > > Jun 10 18:51:06 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux) and do record
> > > audio clip with mixmonitor() as alaw file (softphone is also configured
> > > with alaw active only). Using file command i can get the following
> > > information
> > >
> > > 983006584-20100517-125002.alaw: RIFF (little-endian) data, WAVE audio,
> > > ITU G.711 A-law, mono 8000 Hz
> > >
> > > But when i install the same system on Centos 5.5 (kernel 2.6.18-92.el5
> > > #1 SMP Tue Jun 10 18:51:06 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux) i
> > > could get the same information with file command. File command
> > > recognized alaw file as JPEG image:
> > >
> > > 983006584-20100517-123825.alaw: JPEG image data
> > >
> > > I guess i may miss something when i setup the new on on Centos 5.5, but
> > > u dont know what it is. Anyone have idea about this?
> > >
> > > please help.
> > >
> > > Thanks in advance.
> > > Quyps
> >
> > I did check content of two alaw files (using a hex editor) generated
> > from two aboves cases. For the one fromo CentOS 5.2, beginning bytes
> > look likes :
> >
> > RIFF1^0.WAVEfmt........ at ...@.......fact.....^0.data.^0...
> >
> > and the one from CentOS 5.5
> >
> > ......................RQVTV........XEMBAX............
> >
> > It seem like the first one have some information about file format,
> > which make our convert tool works correctly, and which the second one
> > doesnt have.
> >
> > Can you explain to me this different, and how can i get the information
> > as the first one?
> >
> > Thanks in advances,
> > Quyps
>
> This question have been asked for a while, I really need some help
> here?
>
> Thanks in advance.
> Quyps
>
>
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-- 
Steve Murphy
ParseTree Corp
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