Converting PCM-ALAW data to an audio file using ffmpeg

Question

In my project, I processed the received RTP packets with the payload, and extracted all the payload to a separate buffer. This payload is - PCM ALAW (Type 8). How do I implement a class that will take as arguments - the file name and a buffer with raw data to create an audio file. Exactly what steps do I have to go through in order to encode raw data into an audio file? As an example, I used this example.

Answer 1

That sounds way too complex. "PCM ALAW" is a bit misleading, but it's pretty clear that G.711 aLaw encoding is meant. That's a trivial "compression" which maps each 16 bits PCM sample to an 8 bits value. So a trivial lookup fixes that.

There's even a Free implementation of the aLaw encoding available. Just convert each sample to 16 bits PCM, stuff a standard Microsoft WAVE header in front of it, and call the result .WAV .

You'll need to fill in a few WAV headers based on the RTP type 8. Chiefly, that's "Mono, 8000 Hz, 16 bits per sample". One small problem with the header is that you can only write the full header once you know how many samples you have. You could update the header whenever you receive a RTP packet, but that's a bit I/O intensive. It might be nicer to do that once per 10 packets or so.