# Getting Started
The easiest way to start using Oboe is to build it from source by adding a few steps to an existing Android Studio project.

## Adding Oboe to your project

### 1. Clone the github repository 
Start by cloning the [latest stable release](https://github.com/google/oboe/releases/) of the Oboe repository, for example: 

    git clone -b 1.1-stable https://github.com/google/oboe

**Make a note of the path which you cloned oboe into - you will need it shortly**

### 2. Update CMakeLists.txt
Open your app's `CMakeLists.txt`. This can be found under `External Build Files` in the Android project view. If you don't have a `CMakeLists.txt` you will need to [add C++ support to your project](https://developer.android.com/studio/projects/add-native-code).

![CMakeLists.txt location in Android Studio](images/cmakelists-location-in-as.png "CMakeLists.txt location in Android Studio")

Now add the following commands to the end of `CMakeLists.txt`. **Remember to update `**PATH TO OBOE**` with your local Oboe path from the previous step**:

    # Set the path to the Oboe directory.
    set (OBOE_DIR ***PATH TO OBOE***) 
    
    # Add the Oboe library as a subdirectory in your project.
    add_subdirectory (${OBOE_DIR} ./oboe) 
    
    # Specify the path to the Oboe header files.
    include_directories (${OBOE_DIR}/include)  


In the same file find the [`target_link_libraries`](https://cmake.org/cmake/help/latest/command/target_link_libraries.html) command. 
Add `oboe` to the list of libraries which your app's library depends on. For example:

    target_link_libraries(native-lib oboe)

Here's a complete example `CMakeLists.txt` file:

    cmake_minimum_required(VERSION 3.4.1)

    # Build our own native library
    add_library (native-lib SHARED src/main/cpp/native-lib.cpp )

    # Specify the libraries which our native library is dependent on, including Oboe
    target_link_libraries (native-lib log oboe)
    
    # Build the Oboe library
    set (OBOE_DIR ../../../oboe)  
    add_subdirectory (${OBOE_DIR} ./oboe) 
    
    # Make the Oboe public headers available to our app
    include_directories (${OBOE_DIR}/include)

Now go to `Build->Refresh Linked C++ Projects` to have Android Studio index the Oboe library. 

Verify that your project builds correctly. If you have any issues building please [report them here](issues/new).

# Using Oboe
Once you've added Oboe to your project you can start using Oboe's features. The simplest, and probably most common thing you'll do in Oboe is to create an audio stream. 

## Creating an audio stream
Include the Oboe header:

    #include <oboe/Oboe.h>

Streams are built using an `AudioStreamBuilder`. Create one like this:

    oboe::AudioStreamBuilder builder;

Use the builder's set methods to set properties on the stream (you can read more about these properties in the [full guide](FullGuide.md)):

    builder.setDirection(oboe::Direction::Output);
    builder.setPerformanceMode(oboe::PerformanceMode::LowLatency);
    builder.setSharingMode(oboe::SharingMode::Exclusive);
    builder.setFormat(oboe::AudioFormat::Float);
    builder.setChannelCount(oboe::ChannelCount::Mono);

Define an `AudioStreamCallback` class to receive callbacks whenever the stream requires new data.

    class MyCallback : public oboe::AudioStreamCallback {
    public:
        oboe::DataCallbackResult
        onAudioReady(oboe::AudioStream *audioStream, void *audioData, int32_t numFrames) {
            
            // We requested AudioFormat::Float so we assume we got it. For production code always check what format
	    // the stream has and cast to the appropriate type.
            auto *outputData = static_cast<float *>(audioData);
	    
            // Generate random numbers centered around zero.
            const float amplitude = 0.2f;
            for (int i = 0; i < numFrames; ++i){
                outputData[i] = ((float)drand48() - 0.5f) * 2 * amplitude;
            }
	    
            return oboe::DataCallbackResult::Continue;
        }
    };

You can find examples of how to play sound using digital synthesis and pre-recorded audio in the [code samples](../samples). 

Supply this callback class to the builder:

    MyCallback myCallback;
    builder.setCallback(&myCallback);

Open the stream:

    oboe::AudioStream *stream;
    oboe::Result result = builder.openStream(&stream);

Check the result to make sure the stream was opened successfully. Oboe has a convenience method for converting its types into human-readable strings called `oboe::convertToText`:

    if (result != oboe::Result::OK) {
        LOGE("Failed to create stream. Error: %s", oboe::convertToText(result));
    }

Note that this sample code uses the [logging macros from here](https://github.com/googlesamples/android-audio-high-performance/blob/master/debug-utils/logging_macros.h).

Check the properties of the created stream. The **format** is one property which you should check. This will dictate the `audioData` type in the `AudioStreamCallback::onAudioReady` callback.

    oboe::AudioFormat format = stream->getFormat();
    LOGI("AudioStream format is %s", oboe::convertToText(format));

Now start the stream. 

    stream->requestStart();

At this point you should start receiving callbacks.

When you are done with the stream you should close it:

    stream->close();

Note that `close()` is a blocking call which also stops the stream.

## Obtaining optimal latency
One of the goals of the Oboe library is to provide low latency audio streams on the widest range of hardware configurations. On some devices (namely those which can only use OpenSL ES) the "native" sample rate and buffer size of the audio device must be supplied when the stream is opened. 

Oboe provides a convenient way of setting global default values so that the sample rate and buffer size do not have to be set each time an audio stream is created.

Here's a code sample showing how the default values for built-in devices can be passed to Oboe:

*MainActivity.java*

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1){
        AudioManager myAudioMgr = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
        String sampleRateStr = myAudioMgr.getProperty(AudioManager.PROPERTY_OUTPUT_SAMPLE_RATE);
	    int defaultSampleRate = Integer.parseInt(sampleRateStr);
	    String framesPerBurstStr = myAudioMgr.getProperty(AudioManager.PROPERTY_OUTPUT_FRAMES_PER_BUFFER);
	    int defaultFramesPerBurst = Integer.parseInt(framesPerBurstStr);

	    native_setDefaultSampleRate(defaultSampleRate);
	    native_setDefaultFramesPerBurst(defaultFramesPerBurst);
	}

*jni-bridge.cpp*

	JNIEXPORT void JNICALL
	Java_com_google_sample_oboe_hellooboe_MainActivity_native_1setDefaultSampleRate(JNIEnv *env,
	                                                                                  jclass type,
	                                                                                  jint sampleRate) {
	    oboe::DefaultStreamValues::SampleRate = (int32_t) sampleRate;
	}

	JNIEXPORT void JNICALL
	Java_com_google_sample_oboe_hellooboe_MainActivity_native_1setDefaultFramesPerBurst(JNIEnv *env,
	                                                                                      jclass type,
	                                                                                      jint framesPerBurst) {
	    oboe::DefaultStreamValues::FramesPerBurst = (int32_t) framesPerBurst;
	}

# Further information
- [Code samples](https://github.com/google/oboe/tree/master/samples)
- [Full guide to Oboe](FullGuide.md)