Let’s define what we need from the audio driver in our synthesizer app in terms of a purely virtual class, an interface: Classes involved in the audio playback in our synthesizer app. We can summarize this design on the following diagram:įigure 1. Therefore, we must use a 2-way abstraction so that Oboe doesn’t know concrete classes that use it and our app doesn’t know which audio driver we are using. We can do it by subclassing oboe::AudioStreamDataCallback.īut then we will make our app dependent on the Oboe library, right? To connect to Android’s audio driver using the Oboe library, we need to implement the audio stream setup, starting, stopping, and the audio callback. They would risk too much of their reputation by accepting the possibility of a glitch □ How to Connect to Android Audio Using Oboe? Unfortunately, any app that has audible glitches in the audio output cannot be used by professional musicians. If we take too much time to generate the samples, an underrun will occur, which manifests itself through glitches in the audio output. wait for an asynchronous task completion.Īll the above examples require calls to OS APIs and as such have no time constraint guarantees.In particular we mustn’t do the following on the audio thread: That means that we never ever can block the audio thread. The callback must return a specified number of samples in time much shorter than these samples represent. The audio callback is called by the audio driver from a dedicated thread, often called the audio thread. The audio callback is called until the output stream is closed, for example, by calling stop(). The generated samples to be played back should be placed in a dedicated buffer supplied by the audio driver. The time interval specifies how many samples should be generated by the audio callback. When the output playback stream is running, the audio callback is called at regular time intervals, for example, every 10 milliseconds. The audio callback is a function defined by a software developer that is supplied to the audio driver. a command to stop output playback stream, stop(), and.a command to start output playback stream, play(),.Their operating principle is quite simple.Ī typical audio driver API contains the following 3 concepts: In all operating systems (OSs), we have at least one audio driver. So that’s exactly what we’ll do! (Additionally, I think it’s the most developer-friendly option of the three). It tries to use AAudio underneath whenever it can and falls back on OpenSL ES when AAudio is not available. The third option is a C+±style wrapper for the previous two. However, it is only supported from Android 8.0, which means it will not run on older Android devices. The second one is a more modern approach containing useful features for professional audio apps. The first one is a “nasty, low-level” (IMO) C-style API. On Android, we have 3 audio APIs that we can use to control the sound playback: Our synthesizer won’t be very complicated but it will need the fine-grained control of the audio driver interaction. Option 1 is sufficient when we want to perform very simple audio tasks, for example, play back a single sound. write a callback for the Android audio driver using one of the available audio APIs in the C language.To play back sound on Android, we have 2 options: How To Play a Sound on Android From Code? Initialization in the WavetableSynthesizer Class.AudioPlayer and oboe::AudioStreamDataCallback implementer.How to Connect to Android Audio Using Oboe?.How To Play a Sound on Android From Code?.Today play back sound we will! Table of Contents We said that it would be necessary to play back sound in our app. In the last episode, we learned how to call the C++ code from Kotlin. In this tutorial series, we are building a synthesizer music app on Android using all the modern (as of 2022) tools and best practices. Welcome to the 5th part of the Android wavetable synthesizer app tutorial! Playing Back Audio on Android with C++ (this one).Android Wavetable Synthesizer Tutorial Series Connect to Android’s audio device from C++ code.
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