Android internalsEgor ElizarovSPbSU 2012

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Egor Elizarov SPbSU 20123

Lecture 8

System start up

Media subsystem

yegor.yelizarov(at)gmail.com

http://vk.com/android_internalsRev: 1.1Last update: 06/01/2012

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Previous time

Graphic subsystem role

Main “players”

Renderscript

Double buffering

2D/3D acceleration

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Linux start up flow

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Android init

● Simple “toolbox” to execute boot script

● Android init language (system/core/init/readme.txt)

● Contains tools like chown, chmod, mount, etc.

● Differs from Android toolbox (system/core/toolbox/)

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Android Init Language

● Action – named sequence of commands to be executed on trigger

● Service – named program to be launched

● Command – simple routines from “toolbox”

● Triggers – strings can be used to match certain kind of events

● Options – modifiers to service (ex: user, group)

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Init.rc example

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Android start up flow

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Final system start up

● Remount system (Ex: /data, /system partitions)

● Fix permissions

● Start services and daemons (Ex: mediaserver, rild)

● Setup properties

● Start Zygote and system server (initialize java services)

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Add new command to init

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Media subsystem

● Provides media API

● Provides audio/video processing features

● Restricts access to media and devices

● Use HW acceleration if possible

● Code: frameworks/base/media

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Media services

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Java/middleware interaction

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Standart media player

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Simple stagefright flow

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Stagefright add new decoder

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HW acceleration

● HW accelerated codecs

● Khronos OpenMAX IL – codec level API

● Khronos OpenMAX AL – player level API

● Rendering can be done through DMA

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HW acceleration scheme

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My masters thesis (before)

*

* rowboat-donut branch

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My masters thesis (after)

* rowboat-donut-dsp branch

*

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Audio

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Camera

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Content restrictions

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Next Time

● Power Management

● Sensors

● Input subsystem

● Data storage

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Useful links

● http://vk.com/android_internals

● http://elinux.org/Android_Booting

● $(ANDROID_ROOT)/system/core/init/readme.txt

● http://freepine.blogspot.com/2010/01/overview-of-stagefrighter-player.html

● http://khronos.org

Egor Elizarov SPbSU 201227

Useful links (2)

● http://rxwen.blogspot.com/2010/01/understanding-android-media-framework.html

● http://se.math.spbu.ru/SE/diploma/2010/Elizarov_Egor_544.pdf

● http://dl.google.com/io/2009/pres/Mastering_the_Android_Media_Framework.pdf

● http://www.netmite.com/android/mydroid/development/pdk/docs/audio_sub_system.htm

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Thanks to

Sergey Matyukevich for review and advices (www.linkedin.com/pub/sergey-matyukevich/31/889/769)

Nikolay F. Fominykh for review and advices

Vladimir Barinov for review and advices (http://www.linkedin.com/pub/vladimir-barinov/2a/18a/bab)