[opus] How to get started with opus and C++/JavaScript/WebAsm

[Emily Bowman]

Since everything goes back to the C library anyway (or a variant of it, if
you use, say, emscripten), you're free to use any language you want to
interface with the API. Third-parties have created wrappers for a number of
other languages, like Python, since C is a simple and universal binding.

While most web streams use chunking via DASH these days, which involves
encapsulating packets in ISO-BMFF (MP4), you're perfectly free to just send
raw Opus packets sliced up and the decoder will handle them gracefully.
Even if packets are lost and you have no error correction, the decoding
will resynchronize within one packet, and sound a lot less ugly than the
chirps you get with many other codecs. That was a specific design goal of
the format. The format on disk is exactly identical to the streamed format,
so just concatenating the received packets is a valid and simple way to
save to disk.

For a basic example of using the API from C/C++, check out
https://opus-codec.org/docs/opus_api-1.3.1/group__opus__encoder.html .
There's a bit of boilerplate to initialize it, but not too much, and from
there you can broadcast the encoded packets however you like. DASH is much
more complex, though if you have a library for your platforms of choice
it'll either support Opus natively or be fairly simple to retrofit in.

-Em

On Wed, Dec 2, 2020 at 5:36 PM Juan Gerardo Ruelas Jr <jruel006 at ucr.edu>
wrote:

> I am interested in using the opus codec to stream audio files to a mobile
> app.
>
> I have a couple of questions about how to get started?
>
>    1. How do I generate opus files programmatically with C++? What inputs
>    does it need? Is there a special file format because all the examples I see
>    only have .wav files as inputs.
>    2. Does opus support chunking? For example, breaking a 24 hour long
>    audio into a series of sequential smaller files (say 5 seconds long) to
>    stream them down to a user?
>    3. Does opus support stitching together opus files? Say, after a user
>    receives the 5 second long stream, can I programmatically stitch the files
>    together as they come so as to save the entire 24 hour long audio file for
>    offline use at a later time?
>    4. How do you stream these files programmatically? What is the general
>    approach. Can you do it with node.js? C++? Python? What is most efficient?
>
>    p.s. (when I say audio files I generally mean just voice audio like in
>    audio books)
>
>
> Thank you for your help, I am honestly confused as to how to get started.
>
> - Juan Gerardo Ruelas Jr.
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