neill's microbit play raw audio file - first draft

playsound.py

from microbit import display, sleep, button_a
import audio

def frames_from_file(sndfile, frame):
    while(sndfile.readinto(frame, 32) > 0):
        yield frame

def play_snd(fname):
    frame = audio.AudioFrame()
    with open(fname, 'rb') as sndfile:
        audio.play(frames_from_file(sndfile, frame),wait=False)
        sleep(1000)
        audio.stop()
    del frame

display.show('r')
while True:
    if button_a.is_pressed():
        play_snd('clip.raw')
    sleep(200)
    

resources

• http://microbit-micropython.readthedocs.io/en/latest/audio.html
• http://microbit-micropython.readthedocs.io/en/latest/tutorials/storage.html
• https://microbit-micropython.readthedocs.io/en/latest/filesystem.html
• microfs / ufs command: https://microfs.readthedocs.io/en/latest/
• microfs's Error 28 is "out of space", i think
• someone else using unsigned (untested) https://forum.micropython.org/viewtopic.php?t=3207

and in the context of Grace's target application:

• sending radio messages from makecode-made programs to micropython-made programs:
  https://support.microbit.org/support/solutions/articles/19000053168-receiving-radio-data-from-the-javascript-blocks-editor-within-python

From a suggested plan by David Whale https://twitter.com/gowolade/status/988412562814525440 with one change - this code seems to work much better with unsigned rather than signed bytes for the headerless 8-bit PCM sound files. (There's a huge amount of distortion with the originally suggested format (with my code, which is likely in error).)

This uses the audio example in the microbit micropython docs (by ntoll or markshannon, perhaps): https://github.com/bbcmicrobit/micropython/blob/master/examples/waveforms.py

Issues:

• there's some clicking at start and stop of sound playback (despite zeros in sample). to investigate.
• this version waits a fixed time for the sound to finish, it doesn't figure it out from the file size and the (fixed) sample playback rate.
• not code related: "ufs put" command won't let me put more than about 7kb without failing with err 28, which seems to be out of space.

Here's another one that triggers on receiving a radio message https://gist.github.com/nbogie/0731380a4b5be26cbed45133d59b38cc
I've also improved it to wait the correct amount of time before closing the audio.