audio - system audio devices
/dev/audio is the directory for the system audio devices. Currently, there are only output devices, so every device file in the directory is an output channel. These channels are numbered, with /dev/audio/0 being the first channel of the first device. To get the audio device to play audio, PCM samples need to be written to it as a series of "frames" (in MPEG terminology) or multi-channel samples with the following format:
| Byte | 0-1 | 2-3 |
|---|---|---|
| Format | 16-bit signed | 16-bit signed |
| Data | Left sample | Right sample |
The sample rate of the samples is determined by the audio device's current sample rate, which may be accessed by an ioctl.
Note that for convenience, the audio device may not block the call to write and return before all the samples were actually transferred to the hardware and/or played by the hardware. For this reason, users need to be aware that the audio device driver's internal buffer may become full and calls to write may return ENOSPC.
ioctlsSOUNDCARD_IOCTL_GET_SAMPLE_RATE: Passes the current device sample rate (in samples per second) into a provided u16* (16-bit unsigned integer pointer).SOUNDCARD_IOCTL_SET_SAMPLE_RATE: Sets the sample rate of the underlying hardware from a provided 16-bit unsigned integer. Note that not all sound cards support all sample rate and the actually achieved sample rate should be checked with the GET_SAMPLE_RATE ioctl.