Using OHAudio for Audio Playback (C/C++)

OHAudio is a set of native APIs introduced in API version 10. These APIs are normalized in design and support both common and low-latency audio channels.

Prerequisites

To use the playback or recording capability of OHAudio, you must first import the corresponding header files.

Linking the Dynamic Library in the CMake Script

target_link_libraries(sample PUBLIC libohaudio.so)

Adding Header Files

Specifically, to use APIs for audio playback, import <native_audiostreambuilder.h> and <native_audiorenderer.h>.

#include <ohaudio/native_audiorenderer.h>
#include <ohaudio/native_audiostreambuilder.h>

Building Audio Streams

OHAudio provides the OH_AudioStreamBuilder class, which complies with the builder design pattern and is used to build audio streams. You need to specify OH_AudioStream_Type based on your service scenarios.

OH_AudioStream_Type can be set to either of the following:

• AUDIOSTREAM_TYPE_RENDERER
• AUDIOSTREAM_TYPE_CAPTURER

The following code snippet shows how to use OH_AudioStreamBuilder_Create to create a builder:

OH_AudioStreamBuilder* builder;
OH_AudioStreamBuilder_Create(&builder, streamType);

After the audio service is complete, call OH_AudioStreamBuilder_Destroy to destroy the builder.

OH_AudioStreamBuilder_Destroy(builder);

How to Develop

Read OHAudio for the API reference.

The following walks you through how to implement simple playback:

1. Create an audio stream builder.

   OH_AudioStreamBuilder* builder;
   OH_AudioStreamBuilder_Create(&builder, AUDIOSTREAM_TYPE_RENDERER);
   

2. Set audio stream parameters.

   After creating the builder for audio playback, set the parameters required.

   // Set the audio sampling rate.
   OH_AudioStreamBuilder_SetSamplingRate(builder, 48000);
   // Set the number of audio channels.
   OH_AudioStreamBuilder_SetChannelCount(builder, 2);
   // Set the audio sampling format.
   OH_AudioStreamBuilder_SetSampleFormat(builder, (OH_AudioStream_SampleFormat)0);
   // Set the encoding type of the audio stream.
   OH_AudioStreamBuilder_SetEncodingType(builder, (OH_AudioStream_EncodingType)0);
   // Set the usage scenario of the audio renderer.
   OH_AudioStreamBuilder_SetRendererInfo(builder, (OH_AudioStream_Usage)1);
   

   Note that the audio data to play is written through callbacks. You must call OH_AudioStreamBuilder_SetRendererCallback to implement the callbacks. For details about the declaration of the callback functions, see OH_AudioRenderer_Callbacks.

3. Set the callback functions.

   OH_AudioRenderer_Callbacks callbacks;
   // Set callbacks for the audio renderer.
   OH_AudioStreamBuilder_SetRendererCallback(builder, callbacks, nullptr);
   

4. Create an audio renderer instance.

   OH_AudioRenderer* audioRenderer;
   OH_AudioStreamBuilder_GenerateRenderer(builder, &audioRenderer);
   

5. Use the audio renderer.

   You can use the APIs listed below to control the audio streams.

6. Destroy the audio stream builder.

   When the builder is no longer used, release related resources.

   OH_AudioStreamBuilder_Destroy(builder);
   

Sample Code

#include <iostream>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <thread>
#include <chrono>
#include <ctime>
#include <ohaudio/native_audiorenderer.h>
#include <ohaudio/native_audiostreambuilder.h>

#ifdef __cplusplus
extern "C" {
#endif
namespace AudioTestConstants {
constexpr int32_t WAIT_INTERVAL = 1000;
} // namespace AudioTestConstants

// Ensure that the file in the directory can be played.
std::string g_filePath = "/data/data/oh_test_audio.pcm";
FILE *g_file = nullptr;
bool g_readEnd = false;
// Audio sampling rate.
int32_t g_samplingRate = 48000;
// Number of audio channels.
int32_t g_channelCount = 2;
// Audio scenario. The value 0 indicates the normal scenario, and 1 indicates the low-latency scenario.
int32_t g_latencyMode = 0;
// Audio sample format.
int32_t g_sampleFormat = 1;

// Callback, through which the played audio data will be written.
static int32_t AudioRendererOnWriteData(OH_AudioRenderer *capturer, void *userData, void *buffer, int32_t bufferLen) {
    size_t readCount = fread(buffer, bufferLen, 1, g_file);
    if (!readCount) {
        if (ferror(g_file)) {
            printf("Error reading myfile");
        } else if (feof(g_file)) {
            printf("EOF found");
            g_readEnd = true;
        }
    }
    return 0;
}

void PlayerTest() {
    OH_AudioStream_Result ret;

    // 1. Create an audio stream builder.
    OH_AudioStreamBuilder *builder;
    OH_AudioStream_Type type = AUDIOSTREAM_TYPE_RENDERER;
    ret = OH_AudioStreamBuilder_Create(&builder, type);

    // 2. Set the parameters required by the audio stream.
    OH_AudioStreamBuilder_SetSamplingRate(builder, g_samplingRate);
    OH_AudioStreamBuilder_SetChannelCount(builder, g_channelCount);
    OH_AudioStreamBuilder_SetLatencyMode(builder, (OH_AudioStream_LatencyMode)g_latencyMode);
    OH_AudioStreamBuilder_SetSampleFormat(builder, (OH_AudioStream_SampleFormat)g_sampleFormat);

    // Set the callback, through which the played audio data will be written.
    OH_AudioRenderer_Callbacks callbacks;
    callbacks.OH_AudioRenderer_OnWriteData = AudioRendererOnWriteData;
    ret = OH_AudioStreamBuilder_SetRendererCallback(builder, callbacks, nullptr);

    // 3. Create an audio renderer instance.
    OH_AudioRenderer *audioRenderer;
    ret = OH_AudioStreamBuilder_GenerateRenderer(builder, &audioRenderer);

    // 4. Start playback.
    ret = OH_AudioRenderer_Start(audioRenderer);

    int timer = 0;
    while (!g_readEnd) {
        std::this_thread::sleep_for(std::chrono::milliseconds(AudioTestConstants::WAIT_INTERVAL));
        int64_t frames;
        OH_AudioRenderer_GetFramesWritten(audioRenderer, &frames);
        printf("Wait for the audio to finish playing.(..%d s) frames:%ld\n", ++timer, frames);
        int64_t framePosition;
        int64_t timestamp;
        OH_AudioRenderer_GetTimestamp(audioRenderer, CLOCK_MONOTONIC, &framePosition, &timestamp);
        printf("framePosition %ld timestamp:%ld\n", framePosition, timestamp);
    }
    // 5. Stop the playback.
    ret = OH_AudioRenderer_Stop(audioRenderer);
    
    // Release the audio renderer instance.
    ret = OH_AudioRenderer_Release(audioRenderer);

    // 6. Destroy the audio stream builder.
    ret = OH_AudioStreamBuilder_Destroy(builder);
}

int main() {
    // Open the file before playback.
    g_file = fopen(g_filePath.c_str(), "rb");
    if (g_file == nullptr) {
        printf("OHAudioRendererTest: Unable to open file \n");
        return 0;
    }
    // Start playback.
    PlayerTest();
    // Close the file after the playback is complete.
    fclose(g_file);
    g_file = nullptr;
    return 0;
}

#ifdef __cplusplus
}
#endif

Setting the Low Latency Mode

If the device supports the low-latency channel, you can use the low-latency mode to create a player for a higher-quality audio experience.

The development process is similar to that in the common playback scenario. The only difference is that you need to set the low delay mode by calling OH_AudioStreamBuilder_SetLatencyMode() when creating an audio stream builder.

The code snippet is as follows:

OH_AudioStream_LatencyMode latencyMode = AUDIOSTREAM_LATENCY_MODE_FAST;
OH_AudioStreamBuilder_SetLatencyMode(builder, latencyMode);