asterisk users - Jan 2009 - u-law file header ?

QUESTION:  Who's in the wrong: 

I recently saw an example of a u-law file with a metadata header on the file.  
The asterisk playback function 'PLAYED' the ascii header values as if
they were audio data, creating an audible 'click'.

After realizing the click was coming from metadata (and fixing it), I became
curious:

Which is 'correct?  In other words:

1. Is it considered incorrect to ever include metadata on a u-law formatted
file?
or 
2. Is it considered incorrect for a playback engine to fail to check for
metadata headers before playback?
or
3. Is it unspecified, and therefore considered incorrect for someone (ME) to
FEED a u-law stream into any playback engine without FIRST making sure that
somebody's two-bit application didn't tack on an unsolicited header? :-)

In other words, should case 1 or 2 be considered a software defect?

Thanks
-Karl



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On Mon, Jan 12, 2009 at 16:15, Karl Fife <karlfife at gmail.com>
wrote:
> QUESTION:  Who's in the wrong:
>
> I recently saw an example of a u-law file with a metadata header on the
> file.
> The asterisk playback function 'PLAYED' the ascii header values as
if they
> were audio data, creating an audible 'click'.
>
> After realizing the click was coming from metadata (and fixing it), I
became
> curious:
>
> Which is 'correct?  In other words:
>
> 1. Is it considered incorrect to ever include metadata on a u-law formatted
> file?
> or
> 2. Is it considered incorrect for a playback engine to fail to check for
> metadata headers before playback?
> or
> 3. Is it unspecified, and therefore considered incorrect for someone (ME)
to
> FEED a u-law stream into any playback engine without FIRST making sure that
> somebody's two-bit application didn't tack on an unsolicited
header? :-)
>
> In other words, should case 1 or 2 be considered a software defect?
No, it is not a defect.

You need to distinguish between the file format and audio codec. They
are independent of each other. You can store ULAW in a WAV file. The
default asterisk sounds (.g729, .ulaw, .alaw) are raw audio files,
thus there is no header. If Asterisk is expecting a raw format file,
it will playback the entire "contents."

If I save a WAV format file encoded in ulaw, name the file .ulaw, and
then play it back in Asterisk, the exact scenario you describe
happens.