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

[Juan Gerardo Ruelas Jr]

Sorry, forgot to cc the opus mailing list...

What is the difference between Ogg-encapsulated Opus packets vs Raw packets?





How does one generate one or the other programmatically?


- Juan

On Thu, Dec 3, 2020 at 9:30 AM Juan Gerardo Ruelas Jr <jruel006 at ucr.edu>
wrote:

> What is the difference between Ogg-encapsulated Opus packets vs Raw
> packets?
>
> How does one generate one or the other programmatically?
>
> - Juan
>
> On Thu, Dec 3, 2020 at 2:10 AM Emily Bowman <silverbacknet at gmail.com>
> wrote:
>
>> Small correction, I just realized while re-reading this that where I said
>> raw Opus packets, I should have said Ogg-encapsulated Opus packets, which
>> is at least a much simpler format than MP4. Raw packets are useful in some
>> contexts but more awkward to work with.
>>
>> - Em
>>
>> On Thu, Dec 3, 2020 at 12:15 AM Emily Bowman <silverbacknet at gmail.com>
>> wrote:
>>
>>> 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.
>>>> _______________________________________________
>>>> opus mailing list
>>>> opus at xiph.org
>>>> http://lists.xiph.org/mailman/listinfo/opus
>>>>
>>>
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