Liquidsoap svn : External encoders

Introduction

You can use any external program that accepts wav or raw PCM data to encode audio data and use the resulting compressed stream as an output, either to a file, a pipe, or even icecast.

When using an external encoding process, uncompressed PCM data will be sent to the process through its standard input (stdin), and encoded data will be read through its standard output (stdout). When using a process that does only file input or output, /dev/stdin and /dev/stdout can be used, though this may generate issues if the encoding process expects to be able to go backward/forward in the file.

External encoders

The main operators that can be used with external encoders are:

In order to use external encoders with these operators, you have to use the %external encoding format. Its syntax is:

%external(channels=2,samplerate=44100,header=true,
          restart_on_crash=false,
          restart_on_new_track,
          restart_after_delay=<int>,
          process="")

The available options are:

Only one of restart_encoder_delay or restart_on_new_track should be used.

The restart mechanism strongly relies on the good behaviour of the encoding process. The restart operation will close the standard input of the encoding process. The encoding process is then expected to finish its own operations and close its standard output. If it does not close its standard output, the encoding task will not finish.

If your encoding process has this issue, you should turn the restart_on_crash option to true and kill the encoding process yourself.

If you use an external encoder with the output.icecast operator, you should also use the following options of output.icecast:

Video support

Videos can also be encoded by programs able to read files in avi format from standard input. To use it, the flag video=true of %external should be used. For instance, a compresed avi file can be generated with ffmpeg using

output.file(
  %external(process="ffmpeg -i pipe:0 -f avi pipe:1",video=true),
  "/tmp/test.avi", s)