How to compress an AVAudioPCMBuffer to m4a file format without writing to disk?

Question

trzy OP

Created May ’23

Replies 3

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Hi,

I'd like to upload audio samples to the OpenAI Whisper API or others that take m4a, mp3, and wav data. I capture from the microphone and perform some basic signal processing to try to filter out non-voice samples and am left with AVAudioPCMBuffer.

It seems there are two approaches:

Use AVAudioConverter to create AVAudioCompressedBuffer in MPEG-4 audio format. I've gotten this working (although I can't verify that the compressed data is valid because I'm unable to export a file with proper MPEG-4 headers).
Use AVAssetWriter, but this writes to disk, which strikes me as inefficient.

Neither of these readily produces a memory buffer with a .m4a file inside.

Am I missing some obvious way to do this? How do people upload compressed audio data to remote endpoints?

I've also explored just trying to create my own MPEG-4 compliant header but I was unable to produce a valid file.

Thanks,

-- B.

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Answer 1

ssmith_c OP

May ’23

I just had a quick glance at the OpenAI Whisper API - the translation and transcription endpoints expect a file, not a stream. Your path of least resistance is likely to be to create a RAM disk using hdiutil. hth, Stuart

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Answer 2

trzy OP

May ’23

Oh gosh, I forgot to say explicitly (although I did tag it) that this is iOS. Just realized that RAM disks aren't an option there. There really isn't any API for producing asset files in memory?

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Answer 3

Championf OP

Sep ’23

use AudioToolBox' API :AudioConverterFillComplexBuffer() it can convert pcm buffer to any other compressed audio format.

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