Trying to use the ocaml-mm library - terminal

Question

I'm trying to use the ocaml-mm package (https://github.com/savonet/ocaml-mm) and trying to run one of the examples for sine_wav.ml
I first installed the package and also installed the ao library, which the sine_wav file uses. Everything compiles, but I get this error when I'm trying to run the file:
ddavidjeong#DESKTOP-60PESIS:~/cs3110/ms/test$ make main
Entering directory '/home/ddavidjeong/cs3110/ms'
Fatal error: exception Failure("Failed to open device")
make: *** [Makefile:2: main] Error 2
ddavidjeong#DESKTOP-60PESIS:~/cs3110/ms/test$
I have no idea what this exception could refer to.

Answer 1

This errors means that the libao library failed to open its default audio device. You can at least check which default device was found by the library by using in utop
#require "ao";;
Ao.get_default_driver ()
```ocaml
Similarly, you can get the list of all audio device found by libao with
```ocaml
Ao.drivers;;
If there is no visible issue with the default driver, and there is some non-default driver available that looks like they might work; it would be possible to try to use another device in sin_wave.ml by replacing the instance of the Mm_ao.writer class in
let ao = new Mm_ao.writer channels sample_rate in
by an instance of
class ao_writer driver channels rate = object
object
val dev = Ao.open_live ~driver ~channels ~rate ~byte_format:`LITTLE_ENDIAN ()
method write buf ofs len =
let s = Audio.S16LE.make buf ofs len in
Ao.play dev s
method close = Ao.close dev
end
with the right driver.
But it is probably better to see why libao cannot open the default device that it selected itself.