~ubuntu-branches/ubuntu/raring/sflphone/raring

Clients can tell the AUHAL units which channels of the device they are interested in. For example, the client may be processing stereo data, but outputting to a six-channel device. This is done by using the kAudioOutputUnitProperty_ChannelMap property. To use this property:

130

131

For Output:

132

Create an array of SInt32 that is the size of the number of channels of the device (Get the Format of the AUHAL's output Element == 0)

133

Initialize each of the array's values to -1 (-1 indicates that that channel is NOT to be presented in the conversion.)

134

135

Next, for each channel of your app's output, set:

136

channelMapArray[deviceOutputChannel] = desiredAppOutputChannel.

137

138

For example: we have a 6 channel output device and our application has a stereo source it wants to provide to the device. Suppose we want that stereo source to go to the 3rd and 4th channels of the device. The channel map would look like this: { -1, -1, 0, 1, -1, -1 }

139

140

Where the formats are:

141

Input Element == 0: 2 channels (- client format - settable)

142

Output Element == 0: 6 channels (- device format - NOT settable)

143

144

So channel 2 (zero-based) of the device will take the first channel of output and channel 3 will take the second channel of output. (This translates to the 3rd and 4th plugs of the 6 output plugs of the device of course!)

145

146

For Input:

147

Create an array of SInt32 that is the size of the number of channels of the format you require for input. Get (or Set in this case as needed) the AUHAL's output Element == 1.

148

149

Next, for each channel of input you require, set:

150

channelMapArray[desiredAppInputChannel] = deviceOutputChannel;

151

152

For example: we have a 6 channel input device from which we wish to receive stereo input from the 3rd and 4th channels. The channel map looks like this: { 2, 3 }

153

154

Where the formats are:

155

Input Element == 0: 2 channels (- device format - NOT settable)

156

Output Element == 0: 6 channels (- client format - settable)

157

158

159

160

----------------------------------------

161

162

Notes on Original implementation:

163

164

by Phil Burk and Darren Gibbs

165

166

Last updated March 20, 2002

167

168

WHAT WORKS

169

170

Output with very low latency, <10 msec.

171

Half duplex input or output.

172

Full duplex on the same CoreAudio device.

173

The paFLoat32, paInt16, paInt8, paUInt8 sample formats.

174

Pa_GetCPULoad()

175

Pa_StreamTime()

176

177

KNOWN BUGS OR LIMITATIONS

178

179

We do not yet support simultaneous input and output on different

180

devices. Note that some CoreAudio devices like the Roland UH30 look

181

like one device but are actually two different CoreAudio devices. The

182

Built-In audio is typically one CoreAudio device.

183

184

Mono doesn't work.

185

186

DEVICE MAPPING

187

188

CoreAudio devices can support both input and output. But the sample

189

rates supported may be different. So we have map one or two PortAudio

190

device to each CoreAudio device depending on whether it supports

191

input, output or both.

192

193

When we query devices, we first get a list of CoreAudio devices. Then

194

we scan the list and add a PortAudio device for each CoreAudio device

195

that supports input. Then we make a scan for output devices.

196

Older »