TV 音频

TV 输入框架 (TIF) 管理器与音频路由 API 配合使用,可支持灵活的音频路径更改。当系统芯片 (SoC) 实现 TV 硬件抽象层 (HAL) 时,每个 TV 输入源(HDMI IN、调谐器等)均提供 TvInputHardwareInfo,用于为音频类型和地址指定 AudioPort 信息。

  • 物理音频输入/输出设备具有相应的 AudioPort。
  • 软件音频输出/输入流表示为 AudioMixPort(AudioPort 的子类)。

然后,TIF 将 AudioPort 信息用于音频路由 API。

Android TV 输入框架 (TIF)

图 1. TV 输入框架 (TIF)

要求

SoC 必须通过以下音频路由 API 支持功能来实现音频 HAL:

音频端口
  • TV 音频输入端口具有相应的音频源端口实现。
  • TV 音频输出端口具有相应的音频接收器端口实现。
  • 可在任意 TV 输入音频端口和任意 TV 输出音频端口之间创建音频通路。
默认输入 AudioRecord(使用默认输入源创建)必须在 Android TV 上采集“虚拟 Null 输入源”,以获取 AUDIO_DEVICE_IN_DEFAULT。
设备环回 需要支持 AUDIO_DEVICE_IN_LOOPBACK 输入,这是所有 TV 输出(11 Khz、16bit 单声道或 48 Khz、16bit 单声道)的所有音频输出的完整组合。仅用于音频采集。

TV 音频设备

Android 支持使用以下设备处理 TV 音频输入/输出。

system/media/audio/include/system/audio.h

注意:在 Android 5.1 及更早版本中,此文件的路径为:system/core/include/system/audio.h

/* output devices */
AUDIO_DEVICE_OUT_AUX_DIGITAL  = 0x400,
AUDIO_DEVICE_OUT_HDMI   = AUDIO_DEVICE_OUT_AUX_DIGITAL,
/* HDMI Audio Return Channel */
AUDIO_DEVICE_OUT_HDMI_ARC   = 0x40000,
/* S/PDIF out */
AUDIO_DEVICE_OUT_SPDIF    = 0x80000,
/* input devices */
AUDIO_DEVICE_IN_AUX_DIGITAL   = AUDIO_DEVICE_BIT_IN | 0x20,
AUDIO_DEVICE_IN_HDMI      = AUDIO_DEVICE_IN_AUX_DIGITAL,
/* TV tuner input */
AUDIO_DEVICE_IN_TV_TUNER    = AUDIO_DEVICE_BIT_IN | 0x4000,
/* S/PDIF in */
AUDIO_DEVICE_IN_SPDIF   = AUDIO_DEVICE_BIT_IN | 0x10000,
AUDIO_DEVICE_IN_LOOPBACK    = AUDIO_DEVICE_BIT_IN | 0x40000,

音频 HAL 扩展

音频路由 API 的音频 HAL 扩展定义如下:

system/media/audio/include/system/audio.h

注意:在 Android 5.1 及更早版本中,此文件的路径为:system/core/include/system/audio.h

/* audio port configuration structure used to specify a particular configuration of an audio port */
struct audio_port_config {
    audio_port_handle_t      id;           /* port unique ID */
    audio_port_role_t        role;         /* sink or source */
    audio_port_type_t        type;         /* device, mix ... */
    unsigned int             config_mask;  /* e.g AUDIO_PORT_CONFIG_ALL */
    unsigned int             sample_rate;  /* sampling rate in Hz */
    audio_channel_mask_t     channel_mask; /* channel mask if applicable */
    audio_format_t           format;       /* format if applicable */
    struct audio_gain_config gain;         /* gain to apply if applicable */
    union {
        struct audio_port_config_device_ext  device;  /* device specific info */
        struct audio_port_config_mix_ext     mix;     /* mix specific info */
        struct audio_port_config_session_ext session; /* session specific info */
    } ext;
};
struct audio_port {
    audio_port_handle_t      id;                /* port unique ID */
    audio_port_role_t        role;              /* sink or source */
    audio_port_type_t        type;              /* device, mix ... */
    unsigned int             num_sample_rates;  /* number of sampling rates in following array */
    unsigned int             sample_rates[AUDIO_PORT_MAX_SAMPLING_RATES];
    unsigned int             num_channel_masks; /* number of channel masks in following array */
    audio_channel_mask_t     channel_masks[AUDIO_PORT_MAX_CHANNEL_MASKS];
    unsigned int             num_formats;       /* number of formats in following array */
    audio_format_t           formats[AUDIO_PORT_MAX_FORMATS];
    unsigned int             num_gains;         /* number of gains in following array */
    struct audio_gain        gains[AUDIO_PORT_MAX_GAINS];
    struct audio_port_config active_config;     /* current audio port configuration */
    union {
        struct audio_port_device_ext  device;
        struct audio_port_mix_ext     mix;
        struct audio_port_session_ext session;
    } ext;
};

hardware/libhardware/include/hardware/audio.h

struct audio_hw_device {
  :
    /**
     * Routing control
     */

    /* Creates an audio patch between several source and sink ports.
     * The handle is allocated by the HAL and should be unique for this
     * audio HAL module. */
    int (*create_audio_patch)(struct audio_hw_device *dev,
                               unsigned int num_sources,
                               const struct audio_port_config *sources,
                               unsigned int num_sinks,
                               const struct audio_port_config *sinks,
                               audio_patch_handle_t *handle);

    /* Release an audio patch */
    int (*release_audio_patch)(struct audio_hw_device *dev,
                               audio_patch_handle_t handle);

    /* Fills the list of supported attributes for a given audio port.
     * As input, "port" contains the information (type, role, address etc...)
     * needed by the HAL to identify the port.
     * As output, "port" contains possible attributes (sampling rates, formats,
     * channel masks, gain controllers...) for this port.
     */
    int (*get_audio_port)(struct audio_hw_device *dev,
                          struct audio_port *port);

    /* Set audio port configuration */
    int (*set_audio_port_config)(struct audio_hw_device *dev,
                         const struct audio_port_config *config);

测试 DEVICE_IN_LOOPBACK

要测试用于 TV 监控的 DEVICE_IN_LOOPBACK,请使用以下测试代码。运行测试后,采集到的音频将保存到 /sdcard/record_loopback.raw 中,您可以使用 FFmpeg 来收听。

<uses-permission android:name="android.permission.MODIFY_AUDIO_ROUTING" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

   AudioRecord mRecorder;
   Handler mHandler = new Handler();
   int mMinBufferSize = AudioRecord.getMinBufferSize(RECORD_SAMPLING_RATE,
           AudioFormat.CHANNEL_IN_MONO,
           AudioFormat.ENCODING_PCM_16BIT);;
   static final int RECORD_SAMPLING_RATE = 48000;
   public void doCapture() {
       mRecorder = new AudioRecord(MediaRecorder.AudioSource.DEFAULT, RECORD_SAMPLING_RATE,
               AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, mMinBufferSize * 10);
       AudioManager am = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
       ArrayList<AudioPort> audioPorts = new ArrayList<AudioPort>();
       am.listAudioPorts(audioPorts);
       AudioPortConfig srcPortConfig = null;
       AudioPortConfig sinkPortConfig = null;
       for (AudioPort audioPort : audioPorts) {
           if (srcPortConfig == null
                   && audioPort.role() == AudioPort.ROLE_SOURCE
                   && audioPort instanceof AudioDevicePort) {
               AudioDevicePort audioDevicePort = (AudioDevicePort) audioPort;
               if (audioDevicePort.type() == AudioManager.DEVICE_IN_LOOPBACK) {
                   srcPortConfig = audioPort.buildConfig(48000, AudioFormat.CHANNEL_IN_DEFAULT,
                           AudioFormat.ENCODING_DEFAULT, null);
                   Log.d(LOG_TAG, "Found loopback audio source port : " + audioPort);
               }
           }
           else if (sinkPortConfig == null
                   && audioPort.role() == AudioPort.ROLE_SINK
                   && audioPort instanceof AudioMixPort) {
               sinkPortConfig = audioPort.buildConfig(48000, AudioFormat.CHANNEL_OUT_DEFAULT,
                       AudioFormat.ENCODING_DEFAULT, null);
               Log.d(LOG_TAG, "Found recorder audio mix port : " + audioPort);
           }
       }
       if (srcPortConfig != null && sinkPortConfig != null) {
           AudioPatch[] patches = new AudioPatch[] { null };
           int status = am.createAudioPatch(
                   patches,
                   new AudioPortConfig[] { srcPortConfig },
                   new AudioPortConfig[] { sinkPortConfig });
           Log.d(LOG_TAG, "Result of createAudioPatch(): " + status);
       }
       mRecorder.startRecording();
       processAudioData();
       mRecorder.stop();
       mRecorder.release();
   }
   private void processAudioData() {
       OutputStream rawFileStream = null;
       byte data[] = new byte[mMinBufferSize];
       try {
           rawFileStream = new BufferedOutputStream(
                   new FileOutputStream(new File("/sdcard/record_loopback.raw")));
       } catch (FileNotFoundException e) {
           Log.d(LOG_TAG, "Can't open file.", e);
       }
       long startTimeMs = System.currentTimeMillis();
       while (System.currentTimeMillis() - startTimeMs < 5000) {
           int nbytes = mRecorder.read(data, 0, mMinBufferSize);
           if (nbytes <= 0) {
               continue;
           }
           try {
               rawFileStream.write(data);
           } catch (IOException e) {
               Log.e(LOG_TAG, "Error on writing raw file.", e);
           }
       }
       try {
           rawFileStream.close();
       } catch (IOException e) {
       }
       Log.d(LOG_TAG, "Exit audio recording.");
   }

/sdcard/record_loopback.raw 中找到采集到的音频文件,并使用 FFmpeg 来收听:

adb pull /sdcard/record_loopback.raw
ffmpeg -f s16le -ar 48k -ac 1 -i record_loopback.raw record_loopback.wav
ffplay record_loopback.wav

用例

本节包括 TV 音频的常见用例。

带有扬声器输出的 TV 调谐器

当 TV 调谐器进入活动状态时,音频路由 API 会在调谐器和默认输出(例如扬声器)之间创建一个音频通路。调谐器输出无需解码,但最终音频输出会与软件 output_stream 混合。

Android TV 调谐器音频通路

图 2. 带有扬声器输出的 TV 调谐器的音频通路。

直播 TV 期间的 HDMI OUT

用户正在观看直播 TV,随后切换到 HDMI 音频输出 (Intent.ACTION_HDMI_AUDIO_PLUG)。所有 output_stream 的输出设备均更改到 HDMI_OUT 端口,而 TIF 管理器将现有调谐器音频通路的接收器端口更改为 HDMI_OUT 端口。

Android TV HDMI-OUT 音频通路

图 3. 来自直播 TV 的 HDMI OUT 音频通路。