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waterzhang0423 / AMRAudioRecorder

Record amr audio on Android, support pause and resume.
MIT License
13 stars 5 forks source link

Pause and Resume Cuts off Beginning of Resume #4

Closed rayliverified closed 7 years ago

rayliverified commented 7 years ago

When recording audio is paused and then resumed, the beginning of the audio upon resuming is cut off. For example, if I record the following bit: "Record Audio Commencing Now (PAUSE) Continue Recording Audio After Pause" It become: "Record Audio Commencing Now --ding Audio After Pause"

There is about 0.8 seconds that is cut off after resuming.

rayliverified commented 7 years ago

Upon further observation, this behavior only occurs sporadically. Weird... Test device: Sony Xperia X Performance.

rayliverified commented 7 years ago

Source of issue found.

Cause: MediaRecorder is not very good for recording audio. Depending on hardware, there is a variable delay on recording audio. When .start() is called on the MediaRecorder object, the file immediately starts writing with no delay. However, the microphone input is not saved for anywhere between 0 - 1.5 seconds depending on the device. The only solution is to use AudioRecorder which has next to no delay. AudioRecorder is very complex to implement and outputting to AMR in my research requires reencoding.

As it stands, this issue CANNOT be fixed because the MediaRecorder class is flawed. Google refuses to fix this issue: https://issuetracker.google.com/issues/36927248

Attempts to work around this issue include trimming AMR bytes to remove the blank audio. Unfortunately, trimming bytes does not work because AMR is encoded. To my best knowledge trimming audio at the beginning would require decoding AMR and then reencoding it. (hopefully I am wrong and there is another way?)

Leaving this issue open for 1 week to allow for discussion.

waterzhang0423 commented 7 years ago

Great work！I did not notice that. According to your work, we should not use MediaRecorder to recording AMR like this way. Seems like that this trick does not work great anymore :)

Maybe we need to find a new solution.

rayliverified commented 7 years ago

I haven't come across and encoder for AMR. Currently, the only way to record to AMR seems to be with the built in Media Recorder. Also, I do not possess the required knowledge to work with Audio Recorder and hardware audio recording. Gotta leave the library be for the time being!