Tik-76.115 Individual Project: Guinea Pig
$Id: gpPlayer.html,v 1.4 1996/04/22 12:17:40 hynde Exp $

The sound player program

The gpPlayer program handles the audio mixing and output of the GuineaPig system. It communicates with the test logic using a text based protocol. A python module gpSoundPlayer provides an easy object oriented access to the player program and hides the communication protocol from the user.

Starting the player

Usually there is no need to start the player manually, the Test Logic will start the player automatically. However, if the player is to be run on a remote host, you have to start it manually. In that case, just run the player program with the parameters you need (see below: Player options). The player will initialize itself and then waits for a connection to the communication socket (can be specified with the '-p port' option). After the connection is established, the player starts producing audio output and accepts commands through the socket. When the player receives a quit-command, it will shut down and the player exits.

If one is using the player outside test logic, the gpSoundPlayer python module can start the player with the launch() method.

Player options

The player program prints the available options with the '-h' option:

# gpPlayer -h
gpPlayer - Sound player server for Guinea Pig
 Usage:
  gpPlayer [ options ... ]
 Options:
   -h          print help and exit
   -m          MONO (1 channel) output
   -s          STEREO (2 channel) output (default)
   -1          same as -m
   -2          same as -s
   -4          4 channel output
   -r rate     set sampling rate (allowed rates: 44100, 22050 and 11025)
   -p port     port number for comm. socket (default 10000)
   -B bufsize  audio buffer size (in sample frames)
   -D          detach from process group
   -N level    set NICE for process

The options are:

-h: Prints the help text above and exits.
-m or -1: Select mono output.
-s or -2: Select stereo output.
-4: Select 4 channel output. Only available in the version for Silicon Graphics machines.
-r samplrate: Selects the output sampling rate. For Linux/MSND allowed values are: 44100 (default), 22050 and 11025. For SGI, the same plus: 48000, 32000, 16000.
-p port: Select port number to use for communications. Default is 10000.
-B bufsize: Set the audio buffer size (in sample frames).
-D: Detach from process group. Prevents a kill signal received by the test logic program from killing the sound player process (when player is launched by the logic module). The test logic usually catches the interrupt and deals with it.
-N nicevalue: Sets nice value of process. If run as root, may be given negative values for more favourable scheduling. May help on systems with no real time priorities.

Features/bugs

Sometimes when the process using the player exits before quitting the player program (does not send the QUIT command to the player), the player program may be left running. Starting a new player process after that will fail because the socket is still in use and the player may have reserved the audio device for itself. If that happens, just kill the old player process with the kill(1) command.

The player can be installed as a SUID root program. It will use the root privileges only when it needs to, that is, during initialization when setting the nice lever for process (running as root allows negative nice values) or when setting real time priority priority. After that the player will switch to the real user id and will not use root privileges any more.

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