Some FLAC files don't decode because LPC order > 12 is not supported
cubetastic33 opened this issue · 6 comments
I want to play some audio files in rust, so I used the rodio crate. Rodio uses claxon for decoding FLAC files, and some files didn't work with rodio.
When I tried the decode_simple.rs example's code from this repo, I got this error: thread 'main' panicked at 'failed to decode FLAC stream: Unsupported("LPC order > 12 is not supported")', src/libcore/result.rs:999:5. Here's a file that doesn't work. (Edit by @ruuda: link to private file removed.)
There is a fairly complicated workaround I came up with, here's the code. This method is, however, pretty slow. Can this feature be implemented in claxon?
Thank you for taking the time to open an issue and for providing a sample file.
There is no fundamental reason that LPC order > 12 is not supported, other than that I never observed it in any real-world file, and subsequently optimized based on that. It should be easy enough to add support for it, I will take a look.
The Flac format defines a "subset" format that places additional restrictions on some parameters, to allow for streaming and to simplify hardware decoders. A maximum LPC order of 12 is one of the requirements of the subset format. All encoders I know of will generate subset files by default. Until now, I had never observed a non-subset file in the wild, but yours is one.
There is a fairly complicated workaround I came up with
As a different workaround, if re-encoding the file is an option for you, you can encode it with flac -8 input.flac -o output.flac. flac will generate subset-compliant files by default.
@cubetastic33 I removed the link to the file from your report. I will include the problematic subframe as a test sample in the repository. This will be such a small sample that the original audio will not be recognizable.
The non-subset-lpc branch contains a version that can decode your file. I will still add a regression test and run the fuzzers before merging it to master.
@ruuda thanks very much for a quick response!
Until now, I had never observed a non-subset file in the wild, but yours is one.
I see. I have more than one of these, too
The non-subset-lpc branch contains a version that can decode your file. I will still add a regression test and run the fuzzers before merging it to master.
Brilliant! Can't wait 😁
Version 0.3.3 and 0.4.2 which include a fix are now on crates.io. Thanks again for reporting!
It would be interesting to scrape the internet for real-world FLAC samples and try running them through both libflac and claxon, then comparing the outputs. Archive.org has a ton of freely-licensed FLACs, but I'm not sure if they provide a reasonable API to scrape them.