Android's Multimedia Framework

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Android's Multimedia
Framework
September 2014
Karim Yaghmour
@karimyaghmour
karim.yaghmour@opersys.com

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About
● Author of:
● Introduced Linux Trace Toolkit in 1999
● Originated Adeos and relayfs (kernel/relay.c)
● Training, Custom Dev, Consulting, ...

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Agenda
● Architecture Basics
● Display Core
● Multimedia Architecture
● App Dev Model
● Kernel Drivers
● HAL definitions
● HAL modules
● System Services
● Stagefright
● Walkthrough
● Relevant Apps
● References and Pointers

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1. Architecture Basics
● Hardware used to run Android
● AOSP
● Binder
● System Services
● HAL

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/frameworks/base/services/java/...
/frameworks/base/services/jni/
/hardware/libhardware/
/device/[MANUF.]/[DEVICE]
/sdk/emulator/
Kernel or module
/frameworks/base/core/...
AOSP-provided
ASL
Manuf.-provided
Manuf. license
Manuf.-provided
GPL-license

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2. Display Core
● Display Hardware
● Display stack in Android
● Kernel driver
● HAL definition
● HAL module
● Surface Flinger
● Window Manager

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2.1. Display Hardware
MMU
IOMMU

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2.2. Display stack in Android

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From source.android.com - CC-BY 2.5

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2.3. Kernel driver
●
Video memory management
●
Mode setting
● Checking of parameters
● Motorola Xoom:
●
/dev/nvhdcp1
● /dev/nvhost-ctrl
● /dev/nvhost-display
● /dev/nvhost-dsi
●
/dev/nvhost-gr2d
● /dev/nvhost-gr3d
●
/dev/nvhost-isp
●
/dev/nvhost-mpe
● /dev/nvhost-vi
● /dev/nvmap
● /dev/tegra-crypto
●
/dev/tegra_avp
●
/dev/tegra_camera
●
/dev/tegra_fuse
● /dev/tegra_rpc
● /dev/tegra_sema
● ... whatever hides in hwcomposer HAL module

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2.3. HAL Definition
● /hardware/libhardware/include/hardware/hwcomposer.h
● struct hwc_procs:
● invalidate()
● vsync()
● struct hwc_composer_device:
● prepare()
● set()
● dump()
● registerProcs()
● query()
● *()

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2.5. HAL module
● Skeleton /hardware/libhardware/modules/hwcomposer.cpp
● /system/lib/hw/hwcomposer.BOARD.so
● /system/lib/hw/gralloc.BOARD.so
● Ex. - Mot Xoom:
● hwcomposer.tegra.so
● gralloc.tegra.so
● Surface Flinger hook:
● /frameworks/native/services/surfaceflinger/DisplayHardware
– HWComposer.cpp
– Provides fake vsync if none is provided in HW

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2.6. Surface Flinger
● Actual server:
● /frameworks/native/services/surfaceflinger
● Client side:
● /frameworks/native/libs/gui
● Client / Server interface:
● ISurfaceComposerClient.cpp
● ISurfaceComposer.cpp
● This is NOT an aidl'ed service
● All communication is manually
marshalled/unmarshalled

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2.7. Window Manager
● Server side:
● /frameworks/base/services/java/com/android/server/wm/
– WindowManagerService.java
– Session.java
● Client side:
● /frameworks/base/core/java/android/view/
– WindowManager.java
– WindowManagerImpl.java
– ViewRootImpl.java
● Interfaces:
● IWindowManager.aidl
● IWindowSession.aidl
● Parameters (incl. z-order):
● See WindowManager.java

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3. Multimedia Architecture
● OpenMAX
● Media Playback
● Audio
● Camera

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3.1. OpenMAX
From Khronos website

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3.2. Media Playback

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3.3. Audio

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3.4. Camera

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4. App Dev Model
● Media Playback
● Audio Record
● Camera

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4.1. Media Playback
● developer.android.com sample:
Uri myUri = ....; // initialize Uri here
MediaPlayer mediaPlayer = new MediaPlayer();
mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
mediaPlayer.setDataSource(getApplicationContext(), myUri);
mediaPlayer.prepare();
mediaPlayer.start();

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From developer.android.com - ASL

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4.2. Audio Record
● developer.android.com steps:
● Create a new instance of android.media.MediaRecorder.
● Set the audio source using MediaRecorder.setAudioSource(). You will probably
want to use MediaRecorder.AudioSource.MIC.
● Set output file format using MediaRecorder.setOutputFormat().
● Set output file name using MediaRecorder.setOutputFile().
● Set the audio encoder using MediaRecorder.setAudioEncoder().
● Call MediaRecorder.prepare() on the MediaRecorder instance.
● To start audio capture, call MediaRecorder.start().
● To stop audio capture, call MediaRecorder.stop().
● When you are done with the MediaRecorder instance, call
MediaRecorder.release() on it. Calling MediaRecorder.release() is always
recommended to free the resource immediately.

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From developer.android.com - ASL

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5. Kernel drivers
● Possibly V4Linux
● Possibly ALSA
● ... whatever hides in multimedia HAL modules

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6. HAL Definition
● /hardware/libhardware/include/hardware/:
● audio_effect.h
● audio.h
● audio_policy.h
● camera.h
● camera2.h
● camera3.h
● camera_common.h

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7. HAL module
● Audio skeletons in /hardware/libhardware/modules/audio
● USB audio in /hardware/libhardware/modules/usbaudio
● Default implementation in /hardware/libhardware/modules/camera
● /system/lib/hw/:
● audio.a2dp.default.so
● audio_policy.default.so
● audio_policy.mpq8064.so
● audio_policy.msm8960.so
● audio.primary.default.so
● audio.primary.mpq8064.so
● audio.primary.msm8960.so
● audio.usb.default.so
● camera.msm8960.so

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8. System Services
● Player
● Audio Flinger
● Audio Policy
● Camera

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8.1. Player
● Actual server:
● frameworks/av/media/libmediaplayerservice
● Client side:
● frameworks/av/media/libmedia
● IMediaPlayerClient.cpp
● IMediaPlayer.cpp
● IMediaPlayerService.cpp
● IMediaRecorderClient.cpp
● IMediaRecorder.cpp

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8.2. Audio Flinger
● Actual Server:
● frameworks/av/services/audioflinger
● Client side:
● IAudioFlingerClient.cpp
● IAudioFlinger.cpp
● IAudioRecord.cpp
● iAudioTrack.cpp

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8.3. Audio Policy
● Actual Server:
● frameworks/av/services/audioflinger
● Client side:
● IAudioPolicyService.cpp

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8.4. Camera
●
Actual Server:
● frameworks/av/services/camera/libcameraservice
● Client Side:
● frameworks/av/camera
● ICameraClient.cpp
● ICamera.cpp
● ICameraRecordingProxy.cpp
● ICameraRecordingProxyListener.cpp
● ICameraService.cpp
● ICameraServiceListener.cpp
● IProCameraCallbacks.cpp
● IProCameraUser.cpp

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8.5. Wrapper process
● All media system services run within
“mediaserver” system process.
● Started by init
● Sources:
● frameworks/av/media/mediaserver

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9. Stagefright
● Multimedia framework
● Houses AwesomePlayer
● Location:
● frameworks/av/media/libstagefright
● Support loadable HW codecs:
● libstagefrighthw.so

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10. Relevant Apps
● Music
● MusicFX
● Gallery2
● SpeechRecorder
● VideoEditor

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11. References and Pointers
● Google's “official” doumentation:
source.android.com/devices/media.html
source.android.com/devices/audio.html
source.android.com/devices/camera/camera.html
● “Use the source, Luke”
●
Developer doc:
● https://developer.android.com/guide/topics/media/mediaplayer.html
● https://developer.android.com/reference/android/media/MediaPlayer.html
● https://developer.android.com/guide/topics/media/audio-capture.html
● “Android Multimedia Framework”, picker - slideshare
●
“The Android media framework”, Bert Van Dam & Poornachandra Kallare, Android Builders Summit
2014
●
“Android’s Stagefright Media Player Architecture”, Ivo Krka,
http://quandarypeak.com/2013/08/androids-stagefright-media-player-architecture/
●
“Mastering the Android Media Framework”, Google I/O 2009
● https://www.khronos.org/openmax/

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Thank you ...
karim.yaghmour@opersys.com

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Acknowledgements:
● Some figures and snippets taken from Google's
Android documentation at
developer.android.com and source.android.com
distributed under the Apache 2.0 license and/or
CC-BY-SA 2.5.

Android's Multimedia Framework

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