Mixing op_raw_seek() and op_pcm_seek()

[ringtailsoftware]

I'm working with opusfile on a microcontroller and am trying to speed up seek operations.

My application needs to seek to a known PCM sample so uses op_pcm_seek(). I can see that op_raw_seek() is much faster but it isn't behaving as I'd expect.

My application is looping an audio clip, I am doing something like the following:

op_pcm_seek(of, pcmStartIndex);
rawIndex = op_pcm_tell(of);
...
op_raw_seek(rawIndex)

However, after op_raw_seek() I notice that the first fraction of a second of audio is missing in playback.

Should this work, or is there something else I need to do to work with op_raw_seek()?

Is there a better way of achieving a fast PCM accurate seek?

Thanks.

[zlago]

opus requires decoding 80ms of audio for the decoder to 'sync' https://datatracker.ietf.org/doc/html/rfc7845.html#section-4.6

you probably want to seek 4800 samples (80ms preroll + you are probably using 20ms sized packets) before your target then op_raw_tell

or while live decoding, keep saving the raw offset as long as you are more than 3840 samples before the target

you can use the raw offset you acquired that way with op_raw_seek, the library should decode 80ms of preroll, and you should be 0ms-20ms before your target. op_pcm_seek to it, opusfile will detect that your target is less than 20ms away and decode to it instead of performing a search

opusfile/src/opusfile.c

Line 2628 in 6dfd29e

/*For small (90 ms or less) forward seeks within the same link, just decode

i am merely a user who wanted to ask the exact same thing before i found your issue, and made an educated guess at how to make this work based on my opus format knowledge and the contents of your issue, this is untested but i think itll work!