bitPickups/android-audio-recorder
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android-audio-recorder/docs/README.md
Alexey Kuznetsov a3d42ff9f0 readme comments on raw format
2024-09-26 23:46:23 +03:00

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Know bugs

None

Recording locations

Android has several storage locations:

  • /data/data/ - internal user storage on new android
  • /storage/self/primary/ - internal storage
  • /storage/emulated/0/ - external storage (sdcard formated as internal or emulated external)
  • /storage/1D13-0F08/ - sdcard formated as portable

Some Androids can have more:

/storage/sdcard - emulated external sdcard /data/user/0/ - internal user storage /sdcard - link for default extenral storage /storage/emulated/0/

Plus application / user specified folders (all combinations of):

  • .../Android/data/com.github.axet.audiorecorder/files
  • .../com.github.axet.audiorecorder/files
  • .../Audio Recorder

For example:

  • /data/data/com.github.axet.audiorecorder/files
  • /data/user/0/com.github.axet.audiorecorder/files
  • /sdcard/Android/data/com.github.axet.audiorecorder/files
  • /sdcard/Audio Recorder

Raw format

Temporary recordings stored inside application specific data folders (described in Recording locations) with following format:

  • Signed 16-bit PCM (2 bytes) or (4 bytes) Float (depends on Settings/Audio Format user setup)
  • Big Endian
  • 1 or 2 channels (depends on user settings). First 2/4 bytes for left channel, second 2/4 bytes for right channel.
  • 16hz to 48hz Sample Rate / Frequincy (depends on user settings)

Android supports 16-bit PCM format or PCM float. Android recomends to use PCM float over 24-bit PCM format or 16-bit PCM if possible.

float mantisa is 23 bits (plus sign bit and float point bits) persition in range from -1..1 can hold about 2,130,706,431 unique numbers which is equivalent to 31 bits integer. When 24-bit PCM only gives you 2^24=16,777,216 unique values.

Adb commands

# adb shell am start -n com.github.axet.audiorecorder/.activities.RecordingActivity

# adb shell am broadcast -a com.github.axet.audiorecorder.STOP_RECORDING