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lao

This is a Lua module with bindings to libao the Cross Platform Audio Output Library, to provide Lua with portable audio output.

API

Data Structures
device
info
options
sampleFormat

Environment Setup/Teardown
ao.initialize
ao.shutdown
ao.appendGlobalOption

Device Setup/Playback/Teardown
ao.openLive
ao.openFile
device:play
device:close

Driver Information
ao.driverId
ao.defaultDriverId
ao.driverInfo
ao.driverInfoList

Miscellaneous
ao.isBigEndian
ao.array2string

Summary

lao sticks to libao principles, but ensures you're still writing Lua. The API is similar to libao's, but simplified so you don't have to deal with a special type of userdata containing the sample formats, options etc. Follow these steps:

• local ao = require("ao")
• Unlike in libao, ao.initalize is called automatically; but you can still call it by hand to restart libao if you've called ao.shutdown
• Call ao.defaultDriverId to get the ID number of the default output driver. If you want to specify a particular output driver, you may call ao.driverId with a string corresponding to the short name of the device (i.e. "oss", "wav", etc.) instead
• If you are using the default live output driver, no extra options are needed. If you want special options, you supply a table of options to the ao.open function
• local device = ao.openLive The return value is the device you will use to play things. If you want file output, call ao.openFile instead
• Call device:play on each block of audio
• The following steps are optional since they're done by lao's __gc handlers, but you may want to do them manually for different reasons:
• Call device:close to close the device
• Call ao.shutdown to shutdown the libao environment

Example

   ao = require( "ao" )
   -- Open the default live driver
   default_driver = ao.defaultDriverId()
   format = { bits=16; channels=2; rate=44100; byteFormat="little"; }
   device = assert( ao.openLive(default_driver, format) )
   -- Play a one-second beep
   freq = 440.0
   buffer = {}
   for i = 0,format.rate do    -- one second
      sample = 0.75 * math.sin(2*math.pi*freq*i / format.rate)
      buffer[2*i+1] = sample   -- left
      buffer[2*i+2] = sample   -- right
    end
    device:play( ao.array2string(buffer) )

Installation

Use LuaRocks to install the ao package:

   luarocks install ao

You need libao installed to use lao, and you need the libao headers to build it from source.
For example on debian :

   aptitude install libao-common
   aptitude install libao-dev

To check it installed successfully, you can download and run examples/ao_live.lua
You should hear a 440-Hz sine wave for about a second.
And also examples/ao_file.lua
which should generate a file beep.wav containing the same sine wave.

See Also

thelinx.github.com/lao
xiph.org/ao/doc/libao-api.html
luarocks.org/modules/peterbillam/ao