xref: /docs/en/application-dev/media/avcodec/audio-decoding.md (revision e41f4b71)

# Audio Decoding

You can call the native APIs provided by the AudioCodec module to decode audio, that is, to decode media data into PCM streams.

Currently, the following decoding capabilities are supported:

| Container Format| Audio Decoding Type                |
| -------- | :--------------------------- |
| mp4      | AAC, MPEG (MP3), FLAC, Vorbis<!--RP1--><!--RP1End--> |
| m4a      | AAC                          |
| flac     | FLAC                        |
| ogg      | Vorbis<!--RP2--><!--RP2End-->    |
| aac      | AAC                          |
| mp3      | MPEG (MP3)                    |
| amr      | AMR (AMR-NB and AMR-WB)           |
| raw      | G711mu                       |
| ape      | APE                          |

**Usage Scenario**

- Audio playback

  Decode audio and transmit the data to the speaker for playing.
- Audio rendering

  Decode audio and transmit the data to the audio processing module for audio rendering.
- Audio editing

  Decode audio and transmit the data for audio editing (for example, adjusting the playback speed of a channel). Audio editing is performed based on PCM streams.
> **NOTE**
>
> Streams generated in the MP3 audio encoding process cannot be directly decoded through the MP3 audio decoding process. The following process is recommended: PCM stream -> MP3 audio encoding -> muxing -> demuxing -> MP3 audio decoding.

## How to Develop

Read [AudioCodec](../../reference/apis-avcodec-kit/_audio_codec.md) for the API reference.

Refer to the code snippet below to complete the entire audio decoding process, including creating a decoder, setting decoding parameters (such as the sampling rate, bit rate, and number of audio channels), and starting, refreshing, resetting, and destroying the decoder.

During application development, you must call the APIs in the defined sequence. Otherwise, an exception or undefined behavior may occur.

The figure below shows the call relationship of audio decoding.

- The dotted line indicates an optional operation.

- The solid line indicates a mandatory operation.

![Call relationship of audio decoding](figures/audio-codec.png)

### Linking the Dynamic Libraries in the CMake Script

```cmake
target_link_libraries(sample PUBLIC libnative_media_codecbase.so)
target_link_libraries(sample PUBLIC libnative_media_core.so)
target_link_libraries(sample PUBLIC libnative_media_acodec.so)
```

### How to Develop

1. Add the header files.

    ```cpp
    #include <multimedia/player_framework/native_avcodec_audiocodec.h>
    #include <multimedia/native_audio_channel_layout.h>
    #include <multimedia/player_framework/native_avcapability.h>
    #include <multimedia/player_framework/native_avcodec_base.h>
    #include <multimedia/player_framework/native_avformat.h>
    #include <multimedia/player_framework/native_avbuffer.h>
    ```

2. Create a decoder instance. In the code snippet below, **OH_AVCodec *** is the pointer to the decoder instance created.

    ```cpp
    // Namespace of the C++ standard library.
    using namespace std;
    // Create a decoder by name.
    OH_AVCapability *capability = OH_AVCodec_GetCapability(OH_AVCODEC_MIMETYPE_AUDIO_MPEG, false);
    const char *name = OH_AVCapability_GetName(capability);
    OH_AVCodec *audioDec_ = OH_AudioCodec_CreateByName(name);
    ```

    ```cpp
    // Specify whether encoding is used. The value false means decoding.
    bool isEncoder = false;
    // Create a decoder by MIME type.
    OH_AVCodec *audioDec_ = OH_AudioCodec_CreateByMime(OH_AVCODEC_MIMETYPE_AUDIO_MPEG, isEncoder);
    ```

    ```cpp
    // Initialize the queues.
    class ADecBufferSignal {
    public:
        std::mutex inMutex_;
        std::mutex outMutex_;
        std::mutex startMutex_;
        std::condition_variable inCond_;
        std::condition_variable outCond_;
        std::condition_variable startCond_;
        std::queue<uint32_t> inQueue_;
        std::queue<uint32_t> outQueue_;
        std::queue<OH_AVBuffer *> inBufferQueue_;
        std::queue<OH_AVBuffer *> outBufferQueue_;
    };
    ADecBufferSignal *signal_;
    ```
   
3. Call **OH_AudioCodec_RegisterCallback()** to register callback functions.

   Register the **OH_AVCodecCallback** struct that defines the following callback function pointers:

    - **OH_AVCodecOnError**, a callback used to report a codec operation error
    - **OH_AVCodecOnStreamChanged**, a callback used to report a codec stream change, for example, audio channel change
    - **OH_AVCodecOnNeedInputBuffer**, a callback used to report input data required, which means that the decoder is ready for receiving data
    - **OH_AVCodecOnNewOutputBuffer**, a callback used to report output data generated, which means that decoding is complete

   You need to process the callback functions to ensure that the decoder runs properly.

    ```cpp
    // Implement the OH_AVCodecOnError callback function.
    static void OnError(OH_AVCodec *codec, int32_t errorCode, void *userData)
    {
        (void)codec;
        (void)errorCode;
        (void)userData;
    }
    // Implement the OH_AVCodecOnStreamChanged callback function.
    static void OnOutputFormatChanged(OH_AVCodec *codec, OH_AVFormat *format, void *userData)
    {
        (void)codec;
        (void)format;
        (void)userData;
    }
    // Implement the OH_AVCodecOnNeedInputBuffer callback function.
    static void OnInputBufferAvailable(OH_AVCodec *codec, uint32_t index, OH_AVBuffer *data, void *userData)
    {
        (void)codec;
        ADecBufferSignal *signal = static_cast<ADecBufferSignal *>(userData);
        unique_lock<mutex> lock(signal->inMutex_);
        signal->inQueue_.push(index);
        signal->inBufferQueue_.push(data);
        signal->inCond_.notify_all();
        // The input stream is sent to inBufferQueue_.
    }
    // Implement the OH_AVCodecOnNewOutputBuffer callback function.
    static void OnOutputBufferAvailable(OH_AVCodec *codec, uint32_t index, OH_AVBuffer *data, void *userData)
    {
        (void)codec;
        ADecBufferSignal *signal = static_cast<ADecBufferSignal *>(userData);
        unique_lock<mutex> lock(signal->outMutex_);
        signal->outQueue_.push(index);
        signal->outBufferQueue_.push(data);
        signal->outCond_.notify_all();
        // The index of the output buffer is sent to outQueue_.
        // The decoded data is sent to outBufferQueue_.
    }
    signal_ = new ADecBufferSignal();
    OH_AVCodecCallback cb_ = {&OnError, &OnOutputFormatChanged, &OnInputBufferAvailable, &OnOutputBufferAvailable};
    int32_t ret = OH_AudioCodec_RegisterCallback(audioDec_, cb_, signal_);
    if (ret != AVCS_ERR_OK) {
        // Exception handling.
    }
    ```

4. (Optional) Call **OH_AudioCodec_SetDecryptionConfig** to set the decryption configuration. Call this API after the media key system information is obtained but before **Prepare()** is called. For details about how to obtain such information, see step 3 in [Media Data Demuxing](audio-video-demuxer.md). For details about DRM APIs, see [DRM](../../reference/apis-drm-kit/_drm.md).  

    Add the header files.

    ```c++
    #include <multimedia/drm_framework/native_mediakeysystem.h>
    #include <multimedia/drm_framework/native_mediakeysession.h>
    #include <multimedia/drm_framework/native_drm_err.h>
    #include <multimedia/drm_framework/native_drm_common.h>
    ```
    Link the dynamic library in the CMake script.

    ``` cmake
    target_link_libraries(sample PUBLIC libnative_drm.so)
    ```

    The following is the sample code:
    ```c++
    // Create a media key system based on the media key system information. The following uses com.clearplay.drm as an example.
    MediaKeySystem *system = nullptr;
    int32_t ret = OH_MediaKeySystem_Create("com.clearplay.drm", &system);
    if (system == nullptr) {
        printf("create media key system failed");
        return;
    }

    // Create a media key session.
    MediaKeySession *session = nullptr;
    DRM_ContentProtectionLevel contentProtectionLevel = CONTENT_PROTECTION_LEVEL_SW_CRYPTO;
    ret = OH_MediaKeySystem_CreateMediaKeySession(system, &contentProtectionLevel, &session);
    if (ret != DRM_OK) {
        // If the creation fails, refer to the DRM interface document and check logs.
        printf("create media key session failed.");
        return;
    }
    if (session == nullptr) {
        printf("media key session is nullptr.");
        return;
    }
    // Generate a media key request and set the response to the media key request.
    // Set the decryption configuration, that is, set the decryption session and secure channel flag to the decoder. (Currently, the secure channel is not supported for audio decryption and therefore the secure channel flag should be set to false.)
    bool secureAudio = false;
    ret = OH_AudioCodec_SetDecryptionConfig(audioDec_, session, secureAudio);
    ```

5. Call **OH_AudioCodec_Configure()** to configure the decoder.

   Key values of configuration options are described as follows:

   |                              |                             Description                            |                AAC                 | FLAC|               Vorbis               | MPEG |       G711mu        |          AMR (AMR-NB and AMR-WB)        |          APE                      |
   | ---------------------------- | :----------------------------------------------------------: | :--------------------------------: | :--: | :--------------------------------: | :--: | :-----------------: | :-------------------------------: | :-------------------------------: |
   | OH_MD_KEY_AUD_SAMPLE_RATE    |                            Sampling rate                           |                Mandatory               | Mandatory|                Mandatory                | Mandatory|        Mandatory         |                Mandatory               |                Mandatory               |
   | OH_MD_KEY_AUD_CHANNEL_COUNT  |                            Number of audio channels                           |                Mandatory               | Mandatory|                Mandatory                | Mandatory|        Mandatory         |                Mandatory               |                Mandatory               |
   | OH_MD_KEY_MAX_INPUT_SIZE     |                         Maximum input size                        |                Optional               | Optional|                Optional                | Optional|        Optional          |               Optional               |                Optional               |
   | OH_MD_KEY_AAC_IS_ADTS        |                           ADTS or not                          |        Optional (Default value: 1 latm)        |  -   |                 -                  |  -   |         -             |               -                  |                 -                  |
   | MD_KEY_AUDIO_SAMPLE_FORMAT   |                        Output audio stream format                       | Optional (SAMPLE_S16LE, SAMPLE_F32LE)|   -   | Optional (SAMPLE_S16LE, SAMPLE_F32LE)|  Optional| Optional (default: SAMPLE_S16LE)| Optional (SAMPLE_S16LE, SAMPLE_F32LE)|               Optional               |
   | MD_KEY_BITRATE               |                             Optional                            |                Optional               | Optional|                Optional               | Optional|         Optional          |              Optional                |               Optional               |
   | MD_KEY_IDENTIFICATION_HEADER |                          ID Header                           |                 -                  |  -   |    Mandatory (Either this parameter or **MD_KEY_CODEC_CONFIG** must be set.)   |  -   |          -            |                -                  |                -                  |
   | MD_KEY_SETUP_HEADER          |                         Setup Header                         |                 -                  |  -   |    Mandatory (Either this parameter or **MD_KEY_CODEC_CONFIG** must be set.)   |  -   |          -            |                -                 |                -                  |
   | MD_KEY_CODEC_CONFIG          | MD_KEY_SETUP_HEADERID Header+Common Header+Setup Header stitching|                 -                  |      |   Mandatory (Either this parameter or the combination of **MD_KEY_IDENTIFICATION_HEADER** and **MD_KEY_SETUP_HEADER** must be selected.)   |  -   |           -            |                -                 |                -                  |
   
   The sample below lists the value range of each audio decoding type.
   | Audio Decoding Type|                                          Sampling Rate (Hz)                                             | Audio Channel Count|
   | ----------- | ----------------------------------------------------------------------------------------------  | :----: |
   | AAC         | 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000, 64000, 88200, 96000                |  1–8  |
   | FLAC       | 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000, 64000, 88200, 96000, 192000        |  1–8  |
   | Vorbis      | 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000, 64000, 88200, 96000, 176400, 192000|  1–8  |
   | MPEG (MP3)   | 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000                                    |  1–2  |
   | G711mu      | 8000                                                                                            |   1    |
   | AMR (amrnb)  | 8000                                                                                            |   1    |
   | AMR (amrwb)  | 16000                                                                                           |   1    |
   | APE         | 8000, 11025, 12000, 16000, 22050, 24000, 32000, 44100, 48000, 64000, 88200, 96000, 176400, 192000|  1–2  |

   ```cpp
   // Set the decoding resolution.
   int32_t ret;
   // (Mandatory) Configure the audio sampling rate.
   constexpr uint32_t DEFAULT_SAMPLERATE = 44100;
   // (Mandatory) Configure the audio bit rate.
   constexpr uint32_t DEFAULT_BITRATE = 32000;
   // (Mandatory) Configure the number of audio channels.
   constexpr uint32_t DEFAULT_CHANNEL_COUNT = 2;
   // (Optional) Configure the maximum input length.
   constexpr uint32_t DEFAULT_MAX_INPUT_SIZE = 1152;
   // Configure whether to use ADTS decoding (ACC).
   constexpr uint32_t DEFAULT_AAC_TYPE = 1;
   OH_AVFormat *format = OH_AVFormat_Create();
   // Set the format.
   OH_AVFormat_SetIntValue(format, OH_MD_KEY_AUD_SAMPLE_RATE, DEFAULT_SAMPLERATE);
   OH_AVFormat_SetIntValue(format, OH_MD_KEY_BITRATE, DEFAULT_BITRATE);
   OH_AVFormat_SetIntValue(format, OH_MD_KEY_AUD_CHANNEL_COUNT, DEFAULT_CHANNEL_COUNT);
   OH_AVFormat_SetIntValue(format, OH_MD_KEY_MAX_INPUT_SIZE, DEFAULT_MAX_INPUT_SIZE);
   OH_AVFormat_SetIntValue(format, OH_MD_KEY_AAC_IS_ADTS, DEFAULT_AAC_TYPE);
   // Configure the decoder.
   ret = OH_AudioCodec_Configure(audioDec_, format);
   if (ret != AV_ERR_OK) {
       // Exception handling.
   }
   ```
   
6. Call **OH_AudioCodec_Prepare()** to prepare internal resources for the decoder.

   ```cpp
   ret = OH_AudioCodec_Prepare(audioDec_);
   if (ret != AV_ERR_OK) {
       // Exception handling.
   }
   ```
   
7. Call **OH_AudioCodec_Start()** to start the decoder.

    ```c++
    unique_ptr<ifstream> inputFile_ = make_unique<ifstream>();
    unique_ptr<ofstream> outFile_ = make_unique<ofstream>();
    // Open the path of the binary file to be decoded.
    inputFile_->open(inputFilePath.data(), ios::in | ios::binary); 
    // Configure the path of the output file.
    outFile_->open(outputFilePath.data(), ios::out | ios::binary);
    // Start decoding.
    ret = OH_AudioCodec_Start(audioDec_);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    ```
   
8. (Optional) Call **OH_AVCencInfo_SetAVBuffer()** to set the Common Encryption Scheme (CENC) information.

    If the content being played is DRM encrypted and demuxing is performed by the upper-layer application, call **OH_AVCencInfo_SetAVBuffer()** to set the CENC information to the AVBuffer so that the media data can be decrypted in the AVBuffer.

    Add the header file.

    ```c++
    #include <multimedia/player_framework/native_cencinfo.h>
    ```
    Link the dynamic library in the CMake script.

    ``` cmake
    target_link_libraries(sample PUBLIC libnative_media_avcencinfo.so)
    ```

    The following is the sample code:
    ```c++
    auto buffer = signal_->inBufferQueue_.front();
    int64_t size;
    int64_t pts;
    uint32_t keyIdLen = DRM_KEY_ID_SIZE;
    uint8_t keyId[] = {
        0xd4, 0xb2, 0x01, 0xe4, 0x61, 0xc8, 0x98, 0x96,
        0xcf, 0x05, 0x22, 0x39, 0x8d, 0x09, 0xe6, 0x28};
    uint32_t ivLen = DRM_KEY_IV_SIZE;
    uint8_t iv[] = {
        0xbf, 0x77, 0xed, 0x51, 0x81, 0xde, 0x36, 0x3e,
        0x52, 0xf7, 0x20, 0x4f, 0x72, 0x14, 0xa3, 0x95};
    uint32_t encryptedBlockCount = 0;
    uint32_t skippedBlockCount = 0;
    uint32_t firstEncryptedOffset = 0;
    uint32_t subsampleCount = 1;
    DrmSubsample subsamples[1] = { {0x10, 0x16} };
    inputFile_.read(reinterpret_cast<char *>(&size), sizeof(size));
    inputFile_.read(reinterpret_cast<char *>(&pts), sizeof(pts));
    inputFile_.read((char *)OH_AVMemory_GetAddr(buffer), size);
    OH_AVCencInfo *cencInfo = OH_AVCencInfo_Create();
    if (cencInfo == nullptr) {
        // Exception handling.
    }
    OH_AVErrCode errNo = OH_AVCencInfo_SetAlgorithm(cencInfo, DRM_ALG_CENC_AES_CTR);
    if (errNo != AV_ERR_OK) {
        // Exception handling.
    }
    errNo = OH_AVCencInfo_SetKeyIdAndIv(cencInfo, keyId, keyIdLen, iv, ivLen);
    if (errNo != AV_ERR_OK) {
        // Exception handling.
    }
    errNo = OH_AVCencInfo_SetSubsampleInfo(cencInfo, encryptedBlockCount, skippedBlockCount, firstEncryptedOffset,
        subsampleCount, subsamples);
    if (errNo != AV_ERR_OK) {
        // Exception handling.
    }
    errNo = OH_AVCencInfo_SetMode(cencInfo, DRM_CENC_INFO_KEY_IV_SUBSAMPLES_SET);
    if (errNo != AV_ERR_OK) {
        // Exception handling.
    }
    errNo = OH_AVCencInfo_SetAVBuffer(cencInfo, buffer);
    if (errNo != AV_ERR_OK) {
        // Exception handling.
    }
    errNo = OH_AVCencInfo_Destroy(cencInfo);
    if (errNo != AV_ERR_OK) {
        // Exception handling.
    }
    ```
   
9. Call **OH_AudioCodec_PushInputBuffer()** to write the data to decode.

   To indicate the End of Stream (EOS), pass in the **AVCODEC_BUFFER_FLAGS_EOS** flag.

    ```c++
    uint32_t index = signal_->inQueue_.front();
    auto buffer = signal_->inBufferQueue_.front();
    int64_t size;
    int64_t pts;
    // size is the length of each frame of the data to decode. pts is the timestamp of each frame and is used to indicate when the audio should be played.
    // The values of size and pts are obtained from an audio and video resource file or data stream to decode.
    // In the case of an audio and video resource file, the values are obtained from the buffer in the decapsulated OH_AVDemuxer_ReadSampleBuffer.
    // In the case of a data stream, the values are obtained from the data stream provider.
    // In this example, the values of size and pts are obtained from the test file.
    inputFile_.read(reinterpret_cast<char *>(&size), sizeof(size));
    inputFile_.read(reinterpret_cast<char *>(&pts), sizeof(pts));
    inputFile_.read((char *)OH_AVBuffer_GetAddr(buffer), size);
    OH_AVCodecBufferAttr attr = {0};
    if (inputFile_->eof()) {
        attr.size = 0;
        attr.flags = AVCODEC_BUFFER_FLAGS_EOS;
    } else {
        attr.size = size;
        attr.flags = AVCODEC_BUFFER_FLAGS_NONE;
    }
    attr.pts = pts;
    OH_AVBuffer_SetBufferAttr(buffer, &attr);
    int32_t ret = OH_AudioCodec_PushInputBuffer(audioDec_, index);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    ```
   
10. Call **OH_AudioCodec_FreeOutputBuffer()** to output decoded PCM streams.

    <!--RP3-->
    ```c++
    uint32_t index = signal_->outQueue_.front();
    OH_AVBuffer *data = signal_->outBufferQueue_.front();
    // Obtain the buffer attributes.
    OH_AVCodecBufferAttr attr = {0};
    ret = OH_AVBuffer_GetBufferAttr(data, &attr);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    // Write the decoded data (specified by data) to the output file.
    pcmOutputFile_.write(reinterpret_cast<char *>(OH_AVBuffer_GetAddr(data)), attr.size);
    ret = OH_AudioCodec_FreeOutputBuffer(audioDec_, index);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    if (attr.flags == AVCODEC_BUFFER_FLAGS_EOS) {
        // End
    }
    ```
    <!--RP3End-->

11. (Optional) Call **OH_AudioCodec_Flush()** to refresh the decoder.

   After **OH_AudioCodec_Flush()** is called, the decoder remains in the running state, but the current queue is cleared and the buffer storing the decoded data is freed. To continue decoding, you must call **OH_AudioCodec_Start()** again.
   
   You need to call **OH_AudioCodec_Start()** in the following cases:

   * The EOS of the file is reached.
   * An error with **OH_AudioCodec_IsValid** set to **true** (indicating that the execution can continue) occurs.

    ```c++
    // Refresh the decoder.
    ret = OH_AudioCodec_Flush(audioDec_);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    // Start decoding again.
    ret = OH_AudioCodec_Start(audioDec_);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    ```

12. (Optional) Call **OH_AudioCodec_Reset()** to reset the decoder.

    After **OH_AudioCodec_Reset()** is called, the decoder returns to the initialized state. To continue decoding, you must call **OH_AudioCodec_Configure()** and then **OH_AudioCodec_Start()**.

    ```c++
    // Reset the decoder.
    ret = OH_AudioCodec_Reset(audioDec_);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    // Reconfigure the decoder.
    ret = OH_AudioCodec_Configure(audioDec_, format);
    if (ret != AV_ERR_OK) {
    // Exception handling.
    }
    ```

13. Call **OH_AudioCodec_Stop()** to stop the decoder.

    ```c++
    // Stop the decoder.
    ret = OH_AudioCodec_Stop(audioDec_);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    }
    ```

14. Call **OH_AudioCodec_Destroy()** to destroy the decoder instance and release resources.

    > **NOTE**
    >
    > You only need to call this API once.

    ```c++
    // Call OH_AudioCodec_Destroy to destroy the decoder.
    ret = OH_AudioCodec_Destroy(audioDec_);
    if (ret != AV_ERR_OK) {
        // Exception handling.
    } else {
        audioDec_ = NULL; // The decoder cannot be destroyed repeatedly.
    }
    ```