convert audio encoding format with ffmpeg

June 30th, 2007 mysurface Posted in ffmpeg, Misc | Hits: 74818 | 4 Comments »

ffmpeg is a very powerful tools, as it is a general tool for audio/video encoding and decoding as well as ripper, converter and even provided API for programmers. I came across a tutorial uses ffmpeg libs for writting a video player less than 1000 lines of codes, which is cool.

I have one time needed to convert a wave file from one encoding format to another because the stream servers at mobile back-end switch only plays wav with a-law encoding format. I have no idea what format is a-law (an ITU standards encoding audio format) at first, and it doesn’t matter. First check the wav file’s encoding info with command call file.

file amazing_grace.wav

The outcomes is this:

amazing_grace.wav: RIFF (little-endian) data, WAVE audio, ITU G.711 A-law, mono 8000 Hz

The target wav must be in this format. So, first of all I would like to check whether is it support a-law encoding?

ffmpeg -formats

Bare in mind, encoder and decoder is not always come in pair, ffmpeg may sometimes only support for decoding but not encoding.

 DEA    pcm_alaw

D - Decoder, E - Encoder and A is audio. Apparently it does support for a-law. So, let us convert it with ffmpeg.

ffmpeg -i imaging.wav -acodec pcm_alaw -ar 8000 imaging1.wav

-i is input file, -ar is audio rate in Hz. Just a slides of time, and you are done. And good thing about command line is you can put that into a bash script to do a batch converts.

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