Playing audio backwards

Question

Hi I'd like to play audio backwards in Android. How do I accomplish it? Any pointers will be appreciated. Thanks.

Have you tried passing a negative sample-rate to AudioTrack.setPlaybackRate? :) — kusma, Feb 02 '11 at 21:20
What about using C code and then trying to compile it with Android? C/C++ code would give you access to the audio file as an array. — Sriram, Feb 04 '11 at 06:37

justin · Accepted Answer · 2011-02-04T05:41:50.747

there probably isn't a functionality in the apis for this.

however, it's quite easy to play pcm audio data backwards.

a demonstration using c++ style pseudo-code:

/* assuming 1 channel (mono), 16 bit LPCM */
const int16_t* const audioFileBuffer = audioFile.audioBuffer();

/* forward */
for (int idx = 0, sampleCount = audioFile.sampleCount(); idx < sampleCount; ++idx) {
    outputBuffer[idx] = audioFileBuffer[idx];
}

/* reverse */
for (int idx = 0, sampleCount = audioFile.sampleCount(), read = audioFile.sampleCount() - 1; idx < sampleCount; ++idx, --read) {
    outputBuffer[idx] = audioFileBuffer[read];
}

score 0 · Answer 2 · answered Feb 02 '11 at 21:15

0

I'm not sure if there is a native way to do it (I am still new to the Android development scene myself) but if it came down to it, you could always try decoding the file yourself in reverse rather than relying on the existing API.

answered Feb 02 '11 at 21:15

codewario

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Playing audio backwards

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