A. When it doesn't have a RIFF WAVE header.
(Since I drafted this post I've had a search around and saw that there is a "known issue with phone posts" in the Support yellow box, plus a few open support requests saying phoneposts don't play, but I can't seem to find discussion of what that issue is. [I have no support privs.])
To cut a long story short, a friend tried out PhonePost today, and I wanted to hear what he had to say. The alleged WAV file he recorded carried a MIME type of audio/wav when I downloaded it, but clearly wasn't one; poking into it, it didn't even have a standard RIFF header (which specifies the sample rate, encoding type etc) - it just seemed to be garbage. (There's a possible related issue here, in that I think my friend specified Ogg Vorbis format for his phone posts, and that was ignored; but he's best placed to take that up.) I tried a few plausible options to
sox but didn't get anywhere.I poked around the LJ CVSweb for clues; eventually downloaded the
libgsm-tools Debian package and was able to use tcat to convert the file into a raw μ-Law which I was then able to pass to sox to play. (tcat -u -p foo.gsm | sox -r 8000 -b -U -t raw - foo.wav was the rune I figured out.)At the very least, it would be nice if the LJ backend would add proper RIFF headers to these files. (I'm assuming GSM is indeed a valid compression scheme for the WAVE format; if it's not, then please stop misrepresenting them!) If GSM is intended to be the "way forward" for non-Vorbis phone posts, then judging by the support board and my experience today there seems to be an urgent support issue to resolve here, or at the very least an FAQ to write on how people should play the darn things.