The supported sound formats (and their proper file extensions) for the Tropo platform are as follows:
- MP3 (*.mp3)
- 8kHz, 8bit u-law (wav or raw) (*.wav or *.ulaw)
- 8kHz, 8bit a-law (wav or raw) (*.wav or *.alaw)
- 8kHz, 8bit pcm (wav) (*.wav)
- 8khz, 16bit pcm (wav or raw) (*.wav or *.pcm)
- MS-GSM (wav) (*.wav)
- GSM 6.10 (raw) (*.gsm)
Using MP3 will result in Tropo automatically down-sampling the audio file to fit the 8-bit, 8 kHz audio of the telephony network. For many files, the downsampling may not result in the best audio quality, so it's always best to have your files in 8bit, 8Khz u-law format from the start.
Audio is streamed directly from the source - the file isn't downloaded first and then the then played. As soon as Tropo has enough of the audio file to start playback, it will. This is usually instantaneous.