Use variable-blocksize encoding consistently in split FLAC tracks#126
Merged
davidnewhall merged 3 commits intogolift:mainfrom Mar 3, 2026
Merged
Conversation
…tracks When a FLAC+CUE file is split into individual tracks, frames that fall entirely within a track were returned from buildOutputFrame as-is from the source stream. For the common case of a fixed-blocksize source (BlockSizeMin == BlockSizeMax), those frames carry HasFixedBlockSize=true in their headers. Boundary-split frames (those that span a track edge) were correctly created with HasFixedBlockSize=false (variable-blocksize). The mix is invalid FLAC: fixed-blocksize frames encode a frame number in the header, while variable-blocksize frames encode a sample position. Decoders such as GStreamer's flacparse detect this inconsistency and abort with streaming stopped, reason error (-5). VLC appears to tolerate it but shows a broken progress bar because the sample positions it reads are meaningless frame-count values treated as sample offsets. Fix: remove the early-return fast path in buildOutputFrame so that every frame written to an output track is freshly constructed with HasFixedBlockSize=false. The mewkiz encoder auto-sets the Num field to the running sample position so no additional tracking is needed. Also zero-out FrameSizeMin/FrameSizeMax in the initial StreamInfo passed to the encoder. The mewkiz encoder has a TODO and never updates those fields on Close(), so copying the source values would embed stale wrong byte-size metadata into every split track. Adds TestCueVariableBlockSizeConsistency to catch regressions. Fixes: Unpackerr/unpackerr#141
… splitting TestCueSplitRealFLAC uses ffmpeg (skipped if not in PATH) to generate a fixed-blocksize FLAC — the encoding all mainstream tools produce — and then exercises ExtractCUE against it. The existing synthetic tests use the mewkiz encoder which already emits variable-blocksize frames, so they never triggered the bug where interior frames were passed through as-is with HasFixedBlockSize=true while boundary-split frames had HasFixedBlockSize=false. The test also includes requireFixedBlocksizeFLAC, which asserts the source file actually has fixed-blocksize encoding, so the test will loudly fail if ffmpeg's behavior ever changes rather than silently passing while no longer covering the relevant code path.
…short vars - buildOutputFrame: remove the origSamples parameter entirely since it is no longer used after the early-return fast-path was deleted; update the sole call site in writeTrackFLAC accordingly - TestCueSplitRealFLAC: switch exec.Command -> exec.CommandContext to satisfy the noctx linter rule - TestCueVariableBlockSizeConsistency / TestCueSplitRealFLAC / requireFixedBlocksizeFLAC: rename short variable f -> trackFile/srcFile to satisfy the varnamelen linter rule
davidnewhall
approved these changes
Mar 3, 2026
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
When a FLAC+CUE file is split into individual tracks, frames that fall entirely within a track were returned from buildOutputFrame as-is from the source stream. For the common case of a fixed-blocksize source (BlockSizeMin == BlockSizeMax), those frames carry HasFixedBlockSize=true in their headers. Boundary-split frames (those that span a track edge) were correctly created with HasFixedBlockSize=false (variable-blocksize).
The mix is invalid FLAC: fixed-blocksize frames encode a frame number in the header, while variable-blocksize frames encode a sample position. Decoders such as GStreamer's flacparse detect this inconsistency and abort with streaming stopped, reason error (-5). VLC appears to tolerate it but shows a broken progress bar because the sample positions it reads are meaningless frame-count values treated as sample offsets.
Fix: remove the early-return fast path in buildOutputFrame so that every frame written to an output track is freshly constructed with HasFixedBlockSize=false. The mewkiz encoder auto-sets the Num field to the running sample position so no additional tracking is needed.
Also zero-out FrameSizeMin/FrameSizeMax in the initial StreamInfo passed to the encoder. The mewkiz encoder has a TODO and never updates those fields on Close(), so copying the source values would embed stale wrong byte-size metadata into every split track.
Adds TestCueVariableBlockSizeConsistency to catch regressions.