Every BlockGroup frame back-patched its element size via ebml::end_master, which
does two stream_position() calls and two real seeks. BufWriter does not override
Seek::stream_position, so each position query is seek(Current(0)) = flush_buf +
lseek — and each of those flushed the 4 MiB BufWriter while every position-moving
seek reset WritebackPipeline::last_flush_pos. The buffer never got to do its job.
An MPEG-2 title takes this path for EVERY frame (the parser stamps a per-frame
duration, so I, P and B all become BlockGroups) — roughly 350,000 per feature.
A BlockGroup's size is knowable before writing, so there is no need to back-patch
at all. New seek-free twins start_master_buf / end_master_buf patch a placeholder
by buffer INDEX instead of file offset, and build_block_group assembles the whole
element into a persistent buffer that write_block_group and its MVC sibling take,
fill, write once, and hand back — including on the error path — so the allocation
is made once rather than per frame.
Measured with a counting writer that, like BufWriter, does not override
stream_position, over 200 frames:
seek calls position-moving
plain before 912 451
plain after 112 51
MVC before 2516 1253
MVC after 116 53
Per-frame cost is now zero; the residual is the header, the per-cluster
back-patch and Cues. For 350k BlockGroups that is 1.4M seek calls removed on the
plain path, 4.2M on an MVC title.
end_master is deliberately NOT changed for its other callers. The Cluster master
genuinely streams — frames are appended to an open cluster over time, so its body
cannot be buffered without holding a whole cluster in memory — and the rest
(EBML header, Tracks, Info, Chapters, Cues) run once, not per frame.
Byte-identity is the safety property, and it is structural: end_master always
patches a FIXED-width 8-byte VINT, and the buffered pair writes and patches
exactly that same placeholder, so the encodings cannot differ. Verified by
capture-then-compare over 200 frames (17 keyframes / 183 non-keyframes, multiple
clusters, BlockDuration present and absent, both reference branches) — output
byte-for-byte identical.
Three tests now pin it permanently: buffered vs seeking output byte-for-byte for
empty/tiny/multi-byte bodies, the same for NESTED masters (the MVC path nests
BlockAdditions > BlockMore, where an index-arithmetic slip would surface), and
end_master_buf erroring rather than panicking on a position outside the buffer.
All three verified red against a deliberately divergent placeholder width.
A note on verifying this kind of change: comparing emitted MKV across two
worktrees at different commits shows a spurious 14-byte difference, because
MuxingApp/WritingApp embed the build's git SHA twice. Compare at the same base.
libfreemkv
Rust library for 4K UHD / Blu-ray / DVD optical drives. Drive access, disc scanning, stream labels, AACS decryption, CSS decryption, KEYDB updates, and content reading in one crate. Drive-level unlocking is handled internally; consumers work with disc access and decryption only.
DVDs (CSS) decrypt out of the box. Blu-ray and UHD (AACS) require a keydb.cfg (default ~/.config/freemkv/keydb.cfg) supplying disc-specific volume unique keys; no AACS key material is compiled in.
12+ MB/s sustained read speeds on BD. Drive prep (init()) handles unlocking internally via the freemkv-unlock crate — clients never see it; when no drive unlock applies, the library rips via the host-certificate AACS handshake.
Multi-lingual by design — the library outputs structured data and numeric error codes, never English text. Build any UI or localization on top.
Part of the freemkv project.
Install
Consumed by git tag (not published to crates.io):
[dependencies]
libfreemkv = { git = "https://github.com/freemkv/libfreemkv", tag = "vX.Y.Z" }
Quick Start
use libfreemkv::{Drive, Disc, ScanOptions};
use std::path::Path;
// Open drive — identified via INQUIRY
let mut drive = Drive::open(Path::new("/dev/sg4"))?;
drive.wait_ready()?; // wait for disc
drive.init()?; // unlock + prep (handled internally)
drive.probe_disc()?; // probe disc surface for optimal speeds
// Scan disc — UDF, playlists, streams, AACS (all automatic)
let disc = Disc::scan(&mut drive, &ScanOptions::default())?;
for title in &disc.titles {
println!("{} — {} streams", title.duration_display(), title.streams.len());
}
// Stream pipeline — read PES frames from any source, write to any output
let opts = libfreemkv::InputOptions::default();
let mut input = libfreemkv::input("iso://Disc.iso", &opts)?;
let title = input.info().clone();
let mut output = libfreemkv::output("mkv://Movie.mkv", &title)?;
while let Ok(Some(frame)) = input.read() {
output.write(&frame)?;
}
output.finish()?;
Multi-pass recovery rip
Recovery moved OUT of this crate in 1.6.0. The sweep/patch strategy, the
ddrescue mapfile, damage classification and the multipass loop now live in the
freemkv-engine crate as freemkv_engine::recovery::{copy, sweep, patch}.
libfreemkv keeps the layers underneath: the raw single-shot read
(Drive::read) and the SCSI-fact translation (SenseFamily) that the engine's
strategy is built on. The dependency runs engine → libfreemkv, so this crate
cannot call into it; front-ends get recovery from the engine directly. See
docs/rip-recovery.md for what stayed here.
What It Does
- Drive access — open, identify, internal unlock + prep, speed control, eject
- 12+ MB/s reads — auto-detects kernel transfer limits, sustained full speed
- Disc scanning — UDF 2.50 filesystem, MPLS playlists, CLPI clip info
- Stream labels — 5 BD-J format parsers (Paramount, Criterion, Pixelogic, CTRM, Deluxe)
- AACS decryption — transparent key resolution and content decrypt (1.0 + 2.0 bus decryption)
- KEYDB updates — download, verify, save from any HTTP URL (zero deps, raw TCP)
- Content reading — adaptive batch reads with automatic decryption
- Stream I/O — unified stream pipeline for reading and writing any format
Streams
| Stream | Input | Output | Transport |
|---|---|---|---|
| DiscStream | Yes | -- | Optical drive via SCSI |
| IsoStream | Yes | -- | Blu-ray ISO image file (read via stream pipeline; written by freemkv_engine::recovery) |
| MkvStream | Yes | Yes | Matroska container |
| M2tsStream | Yes | Yes | BD transport stream with FMKV metadata header |
| NetworkStream | Yes (listen) | Yes (connect) | TCP with FMKV metadata header |
| StdioStream | Yes (stdin) | Yes (stdout) | Raw byte pipe |
| NullStream | -- | Yes | Discard sink (byte counter for benchmarks) |
Streams implement a single unified pes::Stream trait (re-exported as PesStream) exposing read() and write() on one type. input() / output() resolve URL strings to PES stream instances. All URLs use the scheme://path format — bare paths are rejected.
Keys
DVDs (CSS) decrypt out of the box, with no external key file needed.
Blu-rays and UHD (AACS) require a keydb.cfg at ~/.config/freemkv/keydb.cfg (or passed via ScanOptions). No AACS key material is compiled into the binary.
Architecture
Drive — open, identify, init, single-shot read
├── ScsiTransport — SG_IO (Linux), IOKit (macOS), SPTI (Windows)
└── unlock_bridge — private seam to the freemkv-unlock crate
(firmware / AACS cert / CSS bus-auth unlockers)
Disc — scan titles, streams, AACS/CSS state
├── UDF reader — Blu-ray UDF 2.50 with metadata partitions
├── MPLS parser — playlists → titles + clips + streams
├── CLPI parser — clip info → EP map → sector extents
├── IFO parser — DVD title sets, PGC chains, cell addresses
├── Labels — 5 BD-J format parsers (detect + parse)
├── AACS — key resolution + content decryption
├── CSS — DVD CSS (bus auth → player-key disc crack → known-plaintext title-key attack)
└── KEYDB — download + verify + save
Streams — unified PES pipeline
├── PesStream — pes::Stream: one trait, read()/write() PES frames
├── DiscStream — sectors → decrypt → TS demux → PES
├── IsoStream — ISO file → decrypt → TS demux → PES
├── MkvStream — MKV mux/demux
├── M2tsStream — BD transport stream
├── NetworkStream — TCP with FMKV metadata header
├── StdioStream — stdin/stdout pipe
└── NullStream — discard sink
See docs/ for detailed technical documentation on each module.
Error Codes
All errors are structured with numeric codes. No user-facing English text — applications format their own messages.
| Range | Category |
|---|---|
| E1xxx | Device errors (not found, permission) |
| E2xxx | Profile errors (unsupported drive) |
| E3xxx | Unlock errors (failed, signature) |
| E4xxx | SCSI errors (command failed, timeout) |
| E5xxx | I/O errors |
| E6xxx | Disc format errors |
| E7xxx | AACS errors |
| E8xxx | KEYDB update errors |
| E9xxx | Stream / mux errors (URL, PES, ISO, pipeline, demux) |
Platform Support
| Platform | Status | Backend |
|---|---|---|
| Linux | Supported | SG_IO ioctl |
| macOS | Supported | IOKit SCSITask |
| Windows | Supported | SPTI |
Contributing
Run freemkv info disc:// --share with the freemkv CLI to capture your drive's identity for contribution. Drive-unlock profiles are maintained in the freemkv-unlock repository.
License
MIT