Records the channel audio to the specified file until the reception of a defined escape (DTMF) digit. The format argument defines the type of file to be recorded (wav, gsm, etc.). The timeout argument is the maximum number of milliseconds the recording can last, and can be set to -1 for no timeout. The offset_samples argument is optional; if provided, it will seek to the offset without exceeding the end of the file. The BEEP argument will play a beep to the user to signify the start of the record operation. The silence argument is the number of seconds of silence allowed before the function returns despite the lack of DTMF digits or reaching the timeout. The silence value must be preceded by s= and is also optional.

Return values: