Above: two commercial blocks taken out of a 3:45 recording — 133.91 s copied bit-for-bit, 0.93 s re-encoded. 28 frames out of 6743 were touched at all.
The clip is a synthetic test recording, built by
tests/make_demo_media.sh
from nothing but ffmpeg's own sources: colour cards, a fake station logo, and a
15-second commercial grid.
Cutting video normally means decoding and re-encoding the whole file. smartcut re-encodes only the partial GOPs that the cut points fall inside, and copies everything else bit-for-bit.
... I ....... I=========================I ....... I ...
^t_in ^k_first ^k_term ^t_out
|<-head->|<--------- body --------->|<-tail->|
re-encode stream copy re-encode
On real terrestrial recordings over 99% of the output is a lossless copy. A 22-minute, 5-range export driven by the automatic commercial detector came out bit-identical across all 40589 frames.
- Smart rendering — H.264 / HEVC / MPEG-2 / MPEG-4 Part 2. Cutting exactly on an access point re-encodes nothing at all.
- Automatic commercial-boundary detection — reads the junction marks the broadcast puts in its own caption stream, runs of silence, and the presence of the station logo, and reports the runs that land on the 15-second grid. Boundaries snap to access points, so cutting commercials stays entirely lossless.
- Cut-editing GUI — film strip, scene detection, scroll search, and preview playback with audio. What you see is always the edited timeline.
- Built for broadcast material — interlacing is preserved, 2:3 pulldown is
handled on a field-level timeline, and dropped frames, non-zero
start_time, and ARIB ADTS layout are all accounted for. - Output containers — MPEG-TS / MP4 / Matroska, defaulting to the same container and directory as the input.
Codec and track-layout limits apply; see known limitations (Japanese).
Grab a build from Releases. You do not need to install FFmpeg — both builds bundle it.
| Linux | smartcut_0.1.0_amd64.AppImage — needs glibc 2.39+ (Ubuntu 24.04 / Debian 13 / Fedora 40 or newer) |
| Windows | smartcut_0.1.0_x64-setup.exe (installer) or smartcut-portable-x64.zip (unzip and run). x64 only; needs the WebView2 runtime |
To build it yourself, see ビルドと開発 (Japanese).
Drop a file onto the GUI, or use the command line:
smartcut input.ts --keep 5.3-12.7 -o out.ts # keep the given range
smartcut input.ts --cut 8.0-20.0 -o out.ts # drop the given range
smartcut input.ts --analyze # show the plan, write nothing
smartcut input.ts --analyze --detect-cm --logo # commercial candidates
smartcut input.ts --analyze --scenes # scene changes| Option | Meaning |
|---|---|
--keep START-END / --cut START-END |
Ranges; repeatable. 1:23:45.6 form also accepted |
--audio-mode copy|reencode |
copy (default) is lossless with ±10.7ms boundary error; reencode is sample-accurate |
--index scan|container |
How access points are indexed. container is faster but unavailable for TS |
--detect-cm / --logo / --scenes |
Commercial candidates, logo assist, scene detection |
--no-open-gop |
Never start a copy at an open GOP |
-o OUTPUT |
Output path; the extension picks the container |
Cuts are subtractive: the timeline you see is the recording minus the cuts, never the original. A cut region does not turn grey — it disappears. The seek bar shrinks, the film strip closes over the hole, and the frame counter counts the length that will actually be written. All that is left of a cut is a red vertical line at the join.
The status line at the bottom is the plan the engine will execute, before you commit to it: which ranges get copied, which get re-encoded, and how many frames that is.
The documentation is in Japanese. The part worth reading first is 実装上の難所 — the eight reasons why "just cut on GOP boundaries and concatenate" does not work, in the order they were hit.
| Algorithm and pitfalls | How the cut is split, and the eight traps |
| Rust core | Timestamps, mixed SPS/PPS, audio boundaries |
| Validation and limits | Frame-hash verification, real-material results |
| GUI | Editor, thumbnail track, scene detection, playback |
| Commercial detection | Silence plus logo, the 15-second grid, avoiding false positives |
| Broadcast workflow compatibility | PID layout, ADTS, L-SMASH / DGIndex |
| Building ・ Distribution | How to build and ship it |
| BDMV / BDAV ・ Design notes | Research and design decisions |
rust/ Rust core (smartcut_core) and CLI <- the real implementation
gui/ Tauri v2 + vanilla JS GUI
smartcut/ Python reference implementation <- test oracle
tests/ 66 end-to-end test cases
docs/ Documentation
The Python implementation is kept as the reference implementation and test
oracle that pinned down the algorithm and its pitfalls. It shares the same
frame-hash verification with the Rust core, and tests/run_tests.sh and
tests/run_rust_tests.sh report identical lossless ratios.
x264 and x265 are GPL, and linking against them makes the whole application GPL. Re-encoding can also be switched to a hardware encoder (NVENC / QSV / VideoToolbox / AMF). Patent licensing for H.264 / HEVC needs separate consideration for commercial distribution.