Android Audio System
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The document discusses the Android audio system architecture. It is comprised of an Audio Framework layer that includes AudioTrack, AudioRecord and AudioPolicy classes that handle routing audio between apps and the hardware. Below this is the Audio HAL interface that provides read/write functions to the underlying Linux audio driver and hardware. The Audio Flinger manages multiple threads to non-blocking read and write audio data to attached hardware devices. This layered design provides flexibility and handles the real-time audio needs across different Android devices and usage scenarios.
Android Audio System
- 2. Outline • • • • Background Android Audio System Audio Framework Audio HAL 2
- 3. Background 3
- 4. Background • Information about this slide • Software • Android 4.0/4.2 4
- 6. Architecture Audio System • The complexity of android audio system • Soft real-time requirement • Large number of usage scenarios • Software • phone/media player/… • different volume setting/… • Hardware • earpiece/speaker/hdmi/… • mic/bluetooth/… • Flexibility design • good design pattern • performance (Java/JNI/binder/…) 6
- 7. Architecture Audio System Java App Android Framework Audio HAL Linux Driver 7
- 8. Android Audio System pcm data app data flow control flow AudioTrack/AudioRecord/… (AudioPolicy/AudioFlinger/…) Audio Policy Audio Flinger Audio HAL (open/read/write/…) Audio Driver 8
- 10. Audio Framework Network Packet Routing sender 1 router receiver 1 sender 2 Routing path receiver 2 sender 3 receiver 3 sender 4 10
- 11. Audio Framework Audio Routing (play audio) AudioTrack 1 Audio Policy Hardware 1 AudioTrack 2 Audio Flinger Hardware 2 AudioTrack 3 Hardware 3 AudioTrack 4 Java App 11 Audio Framework Audio HAL
- 12. Audio Policy • Decide which thread in AudioFlinger should sound be attached. • stream strategy output • stream : VOICE_CALL, TTS, MUSIC, … • strategy : PHONE, MUSIC, … • output : a thread in AudioFlinger • strategy : bridge between software data stream and hardware 12
- 13. Audio Policy 13
- 14. Audio Policy • IOProfile (audio_policy.conf) • Content • Define all the possible I/O devices • Define default I/O device • Hierarchical structure • hardware module • profile • sampling_rates/channels/formats/devices/flags • With IOProfile, audio policy gets better OO structure. 14
- 15. Audio Policy 15
- 16. Audio Flinger • Several thread to read/write data • Create thread by AudioPolicy • mixer thread • duplicating thread • direct output thread • Resampler • Non-blocking audio I/O • AudioWatchdog 16
- 17. Audio HAL 17
- 18. Audio HAL app AudioTrack/AudioRecord/… (AudioPolicy/AudioFlinger/…) Audio HAL (open/read/write/…) Audio Driver 18
- 19. Audio HAL • ALSA (Advanced Linux Sound Architecture) • unified interface/SMP/thread-safe/… • usespace library • alsa-lib • tinyalsa • tinyplay/tinycap/ tinymix • Audio HAL interface • volume setting • I/O function • … 19
Editor's Notes
- #5: 以前 Mint 有報告過 只講有改到的地方 不講 code，只分享概念
- #7: 有些能關有些不能關 有新裝置時聲音要轉移 同一個東西在不同地方有不同名稱 裝置有 FM 7.1 聲道
- #12: 只講 play 部份，record 反之亦然 有其他諸如 Audio System 之類的裝置管理沒講
- #17: 4.0 -> 4.2 自 7xxx ~ 9xxx (Leo 3926) 相關的自 14xxx ~ 20xxx TODO : 5 ~ 9 FIXME : 4 ~ 28
- #19: 1. The original version is provided from SoC vendor. 2. Dynamic library linked by AudioFlinger.
- #20: Why use Tinyalsa We can use ALSA-lib substitute for Tinyalsacompletely, but we can’t use Tinyalsa substitute for ALSA-lib completely. But,in some times, Tinyalsa can substitute for ALSA-lib to work for some basicfunction. The only reason is that it is smaller and simpler than ALSA-lib. Google Android supplies the Tinyalsa. Audio HAL interface forms changed in Android 4.0.