Save recorded audio to file - OpenSL ES - Android

Question

I'm trying to record from the microphone, add some effects, and the save this to a file

I've started with the example native-audio included in the Android NDK. I'va managed to add some reverb and play it back but I haven't found any examples or help on how to accomplish this.

Any and all help is welcome.

Answer 1

OpenSL is not a framework for file formats and access. If you want a raw PCM file, simply open it for writing and put all buffers from OpenSL callback into the file. But if you want encoded audio, you need your own codec and format handler. You can use ffmpeg libraries, or built-in stagefright.

Update write playback buffers to local raw PCM file

We start with native-audio-jni.c

#include <stdio.h>
FILE* rawFile = NULL;
int bClosing = 0;

...

void bqPlayerCallback(SLAndroidSimpleBufferQueueItf bq, void *context)
{
    assert(bq == bqPlayerBufferQueue);
    assert(NULL == context);
    // for streaming playback, replace this test by logic to find and fill the next buffer
    if (--nextCount > 0 && NULL != nextBuffer && 0 != nextSize) {
        SLresult result;
        // enqueue another buffer
        result = (*bqPlayerBufferQueue)->Enqueue(bqPlayerBufferQueue, nextBuffer, nextSize);
        // the most likely other result is SL_RESULT_BUFFER_INSUFFICIENT,
        // which for this code example would indicate a programming error
        assert(SL_RESULT_SUCCESS == result);
        (void)result;

        // AlexC: here we write:
        if (rawFile) {
            fwrite(nextBuffer, nextSize, 1, rawFile);
        }
    }
    if (bClosing) { // it is important to do this in a callback, to be on the correct thread
        fclose(rawFile);
        rawFile = NULL;
    }
    // AlexC: end of changes
}

...

void Java_com_example_nativeaudio_NativeAudio_startRecording(JNIEnv* env, jclass clazz)
{
    bClosing = 0;
    rawFile = fopen("/sdcard/rawFile.pcm", "wb");

...

void Java_com_example_nativeaudio_NativeAudio_shutdown(JNIEnv* env, jclass clazz)
{
    bClosing = 1;

...

Answer 2

Pass the raw vector from c to java and encode it in mp3 with mediaRecorder, I don't know if you can set the audio source from a raw vector, but maybe...