[asterisk-users] ChanSpy not working - "transmit frame type 64" warning

[James Sneeringer]

When I try to use ChanSpy, the following message is sent repeatedly to
the console (wrapped for readability):

    WARNING[32125]: chan_sip.c:3709 sip_write: Asked to
    transmit frame type 64, while native formats is 0x4 (ulaw)(4)
    read/write = 0x4 (ulaw)(4)/0x4 (ulaw)(4)

This appears to happen because SLINEAR (frame type 64 / 0x40) is not
considered a native format for the channel I'm trying to spy on, so
sip_write() bails.

    DEBUG[32006] chan_sip.c: *** Our native formats are 0x4 (ulaw)
    DEBUG[32006] chan_sip.c: *** Joint capabilities are 0x4 (ulaw)
    DEBUG[32006] chan_sip.c: *** Our capabilities are 0x46 (gsm|ulaw|slin)
    DEBUG[32006] chan_sip.c: *** AST_CODEC_CHOOSE formats are0x4 (ulaw)

The symptom is that the spying listener hears nothing on his or her
handset. The spied-on channel can continue to communicate with the
other end without issue. If I tell ChanSpy to record the call with the
r() option, a .raw file *is* created and does contain the complete
audio stream, so it's at least partly working. The problem appears to
be in converting back from SLINEAR to the spying listener's native
format.

I have format_sln.so loaded, and I have it listed as a valid codec for
all of the SIP devices involved (Polycom 330's and a 550 doing the
spying).

Has anyone else run across this? Maybe there's something really simple
I'm missing?

-James