Bluetooth in Android 4.2 and 4.3(二):AVRCP演化

來源:互聯網
上載者:User

    AVRCP(Audio/Video Remote Control Profile)提供了如下主要功能:

  • 通過藍芽耳機(比如Sony WM600,SBH50)或車載控制台控制手機上音樂播放
  • 在藍芽耳機或車載控制台上顯示手機上音樂播放的狀態,歌名,歌手等資訊
  • 在藍芽耳機或車載控制台上瀏覽手機上的音樂檔案,顯示播放清單

AVRCP有幾個版本,隨著版本的演化,功能不斷增加,以下是具體每個版本的功能:

  • 1.0—Basic remote control commands (play/pause/stop, etc.)
  • 1.3—all of 1.0 plus metadata and media-player state support
    • The status of the music source (playing, stopped, etc.)
    • Metadata information on the track itself (artist, track name, etc.).
  • 1.4—all of 1.0 and 1.3 plus media browsing capabilities for multiple media players
    • Browsing and manipulation of multiple players
    • Browsing of media metadata per media player, including a "Now Playing" list
    • Basic search capabilities
  • 1.5—all of 1.0, 1.3 and 1.4 plus specification corrections and clarifications to absolute volume control, browsing and other features

目前,主流裝置支援到AVRCP 1.3,少部分裝置支援AVRCP 1.4。但是AVRCP 1.4有很多問題,標準不夠明確和完善,因此推出了AVRCP 1.5來修正AVRCP 1.4的問題。AVRCP 1.4最終應該會被廢棄,由AVRCP 1.5來取代它。AVRCP 1.5在功能上和AVRCP 1.4相比,並沒有增加。現在AVRCP還在繼續演化中,比如顯示唱片封面。更多詳細的資料請到bluetooth.org註冊並下載。

    AVRCP定義了兩種role:Controller和Target。藍芽耳機或車載控制台是Controller,手機則是Target。在Android 4.3之前,AOSP(Android Open Source Project)只對AVRCP 1.0提供了支援;一些廠商,比如Sony,和第三方ROM,比如CyanogenMod,在Android上基於BlueZ實現了對AVRCP 1.3/1.4的支援。Android 4.2把Bluetooth stack換成Bluedroid之後,依然只支援AVRCP
1.0,導致一些升級到Android 4.2的手機使用者非常不滿。

    在最新的Android 4.3中,Bluedroid和Media Player終於提供了對AVRCP 1.3的支援。但是何時能提供對AVRCP 1.4/1.5的支援,目前還不得而知。對AVRCP 1.4/1.5的支援,需要Bluedroid和Music Player都做相應的改進,其開發難度要大於對AVRCP 1.3的支援。尤其是Browsing的功能,大量的工作是在Music Player這邊。另外,BlueZ已經支援AVRCP 1.4/1.5,但是還在持續的完善和改進中。

    以下為AVRCP 1.4 spec增加的新內容

  • New Scenarios

    • Remote Control from Car Audio System
The controller(CT) is the car audio system and the mobile phone is the target(TG).The user browsers the available media on the mobile phone via the car interface. The user may then perform actions triggering retrieval of media metadata from the phone, and perform other control operations.
  • New Feature Support

    • Connection establishment for browsing
    • Release connection for browsing
    • Absolute Volume
    • Media Player Selection
      • Supports Multiple Players
    • Browsing
      • Database Aware Players
    • Search
    • Now Playing
      • Playable Folders
  • Sections related New Features

    • 4.1.6 Procedure of AVRCP Browsing commands
    • 4.4.1 PASS THROUGH Command
    • 6.3.2 AVRCP Specific Browsing Commands
    • 6.7.2 RegisterNofitcation
      • Volume Changed 6.13.3
    • 6.9 Media Player Selection
      • SetAdressedPlayer
      • Addressed Player Changed Notification
      • SetBrowsedPlayer
      • Available Players Changed Notification
      • Notify Now Playing Content Changed
    • 6.10 Media Content Navigation
      • Scope: Media Player List, Media Player Virtual Filesystem, Search results, Now Playing
      • Browsable Items
      • UIDs
        • Database Unaware/Aware Players (Without/With UID change detection)
        • UIDs Changed Notification
      • Browsing Commands
    • 6.11 Search
    • 6.12 Item Operations
      • Play item by UID
      • Add-To Now Playing
    • 6.13 Volume Handling
      • SetAbsoluteVomume
      • Notify volume change
    • 6.15.2 Error handling for Breowsing Commands
    • 8 Service Discovery Interoperability Requirements
    • 9 L2CAP Interoperability Requirements
      • Retransmission and Flow Control
      • Configuration of the Browsing Channel
    • 25 List of defined notification events
    • 28 UID scheme

註:以上提到的藍芽耳機特指有LCD顯示和遙控的藍芽耳機。

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