TV Input Framework (TIF) 管理員可搭配音訊路由 API 使用，以便靈活變更音訊路徑。當系統單晶片 (SoC) 實作電視硬體抽象層 (HAL) 時，每個電視輸入 (HDMI IN、Tuner 等) 都會提供 TvInputHardwareInfo，指定音訊類型和位址的 AudioPort 資訊。
- 實體音訊輸入/輸出裝置具有對應的 AudioPort。
- 軟體音訊輸出/輸入串流會以 AudioMixPort (AudioPort 的子類別) 表示。
接著，TIF 會使用 AudioPort 資訊，為音訊路由 API 提供服務。
圖 1. 電視輸入架構 (TIF)
需求條件
SoC 必須實作音訊 HAL，並支援下列音訊路由 API：
| 音訊埠 |
|
|---|---|
| 預設輸入 | AudioRecord (使用 DEFAULT 輸入來源建立) 必須在 Android TV 上取得 AUDIO_DEVICE_IN_DEFAULT 時，搶先取得虛擬空值輸入來源。 |
| 裝置回送 | 必須支援 AUDIO_DEVICE_IN_LOOPBACK 輸入，這是所有電視輸出 (11Khz、16 位元單聲道或 48Khz、16 位元單聲道) 的完整音訊混合。僅用於擷取音訊。 |
電視音訊裝置
Android 支援下列音訊裝置，用於電視音訊輸入/輸出。
system/media/audio/include/system/audio.h
注意：在 Android 5.1 以下版本中，此檔案的路徑為：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,
音訊 HAL 擴充功能
音訊轉送 API 的 Audio HAL 擴充功能定義如下：
system/media/audio/include/system/audio.h
注意：在 Android 5.1 以下版本中，此檔案的路徑為：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);
測試 DEVICE_IN_LOOPBACK
如要測試 DEVICE_IN_LOOPBACK 的電視監控功能，請使用下列測試程式碼。執行測試後，擷取的音訊會儲存至 /sdcard/record_loopback.raw，您可以使用 FFmpeg 聆聽該音訊。
<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.");
}
在 /sdcard/record_loopback.raw 中找出擷取的音訊檔案，然後使用 FFmpeg 聆聽：
adb pull /sdcard/record_loopback.rawffmpeg -f s16le -ar 48k -ac 1 -i record_loopback.raw record_loopback.wavffplay record_loopback.wav
用途
本節說明電視音訊的常見用途。
含喇叭輸出的電視調諧器
電視調諧器啟用後，音訊路由 API 會在調諧器和預設輸出裝置 (例如喇叭) 之間建立音訊補丁。調諧器輸出內容不需要解碼，但最終音訊輸出內容會與軟體 output_stream 混合。
圖 2. 適用於有喇叭輸出的電視調諧器的音訊修補程式。
直播電視期間的 HDMI 輸出
使用者正在觀看電視直播，然後切換至 HDMI 音訊輸出 (Intent.ACTION_HDMI_AUDIO_PLUG)。所有 output_streams 的輸出裝置都會變更為 HDMI_OUT 連接埠，而 TIF 管理員會將現有調諧器音訊修正檔的接收端連接埠變更為 HDMI_OUT 連接埠。
圖 3. 直播電視的 HDMI OUT 音訊修補。