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01d056f794
This properly documents the fact that /dev/audio contains a bunch of device's channels now, instead of being a single file.
25 lines
1.6 KiB
Markdown
25 lines
1.6 KiB
Markdown
## Name
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audio - system audio devices
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## Description
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`/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:
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| Byte | 0-1 | 2-3 |
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|--|:--:|:--:|
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| Format | 16-bit signed | 16-bit signed |
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| Data | Left sample | Right sample |
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The sample rate of the samples is determined by the audio device's current sample rate, which may be accessed by an [ioctl](help://man/2/ioctl).
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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`.
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## Available `ioctl`s
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* `SOUNDCARD_IOCTL_GET_SAMPLE_RATE`: Passes the current device sample rate (in samples per second) into a provided `u16*` (16-bit unsigned integer pointer).
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* `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.
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## See also
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* [Audio-subsystem](help://man/7/Audio-subsystem)
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