Some email clients (e.g. Outlook web/mobile) cannot handle AAC voice messages

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Found related feature proposal:

Use OPUS instead of AAC for audio files

I think audio files could have a lower size maintaining a good quality at lower bitrates (and sample rates but with lower changes) using OPUS format (with opus extension or ogg container) instead of AAC. I made a test to support this using as basic information the constants here deltachat-android/AudioCodec.java at master · deltachat/deltachat-android · GitHub I have used WAV and FLAC (without compression and lossless compression) as base files due a problem with audacity to export directly …