format- Is the format of the file type to be recorded (wav, gsm, etc).
silence- Is the number of seconds of silence to allow before returning.
maxduration- Is the maximum recording duration in seconds. If missing or 0 there is no maximum.
a- Append to existing recording rather than replacing.
n- Do not answer, but record anyway if line not yet answered.
q- quiet (do not play a beep tone).
s- skip recording if the line is not yet answered.
t- use alternate '*' terminator key (DTMF) instead of default '#'
x- Ignore all terminator keys (DTMF) and keep recording until hangup.
k- Keep recorded file upon hangup.
y- Terminate recording if any DTMF digit is received.
This documentation was imported from Asterisk Version SVNGIT-branch-11-r4187133e0eafa