Drag two handles. Hit Trim, or Discord MP4. Done.
A fast MP4 trimmer with live playback, a zoomable thumbnail timeline, and one-click exports that actually fit Discord's upload limit.
| Button | What it does | Size |
|---|---|---|
| ✂ Trim (lossless) | Stream copy. Every track and all Dolby Vision / HDR10 metadata survive bit-exact. Takes seconds. | Same bitrate as the source. A 67 Mbps OBS clip is ~8 MB per second. |
| 💬 Discord MP4 | Re-encodes to H.264 (NVENC on NVIDIA GPUs, x264 otherwise) at a bitrate computed from your Discord tier. Checks the real size afterwards and retries lower if it overshot. | Always under the limit you picked. |
| 🎞 GIF | Palette GIF, steps down size/fps until it fits your tier. | Under the limit, or it tells you to pick a shorter range. |
Every export is copied to the clipboard as a file, so Ctrl+V drops it straight into Discord. Show in folder appears in the status bar.
Auto-update: on launch the app quietly checks the GitHub releases page. When a newer version exists it downloads the installer in the background and shows an "Update to X" button in the status bar; one click installs it and restarts. Manual check: Help -> Check for updates. Set MP4TRIM_NO_UPDATE=1 to disable.
Pick your tier (Free 20 MB, Nitro Basic 50 MB, Nitro 1 GB) in the Discord limit box. It is remembered between runs.
The range label shows the plan live as you drag the handles, for example
Lossless ≈ 415 MB · Discord 50 MB → 1080p60 · 7.0 Mbps ✓.
- Budget = 93% of the limit, minus audio (128 kbps, 96 on the free tier).
- Video bitrate = budget ÷ length, never above the source's own bitrate.
- Highest resolution/fps that still looks clean at that bitrate: 1440p60 → 1080p60 → 1080p30 → 720p60 → 720p30 → 540p30 → 480p30.
- Encode, measure, and re-encode lower if the file came out too big.
If a selection is too long to look acceptable even at 480p it warns you first and tells you the longest length that fits.
Measured on a real 1440p60 AV1 OBS clip (51.5 s, 415 MB lossless):
| Tier | Result |
|---|---|
| 20 MB | ~19 MB, 720p60 |
| 50 MB | 47.3 MB, 1080p60 |
| 1 GB | 439 MB, 1440p60 (source bitrate, nothing to cut) |
- Browse the folder: « and » (or PgUp / PgDn) jump to the previous or next video in the same folder, so you can work through a night of OBS clips without reopening. The status bar shows "clip N of M".
- Fine scrubbing (Apple style): while dragging the playhead or a handle, pull the mouse further below the timeline to slow the drag: ½ speed → ¼ speed → fine (about 3 ms per pixel, finer than one 60 fps frame). A badge above the playhead shows the active speed, and moving back up returns to full speed without jumping.
- Frame-exact scrubbing: dragging never waits on the video player. A scrub engine decodes whole keyframe-to-keyframe chunks into RAM (first frame in ~100 ms, then every frame in the chunk is instant) and the preview shows the true frame for each playhead position, 1:1 with the bar. Releasing the mouse hands the exact position back to normal playback. Uses up to ~420 MB of RAM while scrubbing, freed on close.
- Timeline: thumbnails, time ruler, green in-handle and red out-handle. Scroll to zoom around the cursor (Shift+scroll pans, double-click resets). The thin strip underneath is always the whole file, with your range and the zoom window on it.
- Keyframe warning: lossless cuts can only start on a keyframe. If your in-point is between keyframes the label warns how much earlier the clip will really start; press K to snap to it. Or turn on Options → Frame-accurate trim (re-encodes, drops Dolby Vision).
- Playback uses QtMultimedia (hardware decode + audio). If the system decoder fails on a file it switches to ffmpeg-decoded previews automatically, so colors are always right. HDR is tone-mapped for previews, snapshots, GIFs and Discord MP4s.
- Snapshot: grab the current frame at native resolution, drag to crop, copy to clipboard or save PNG.
- Multiple audio tracks: Discord MP4 uses track 1. Options → Mix all audio tracks mixes them instead (only turn this on if your tracks are different, e.g. game and mic, or the audio doubles in volume).
Everything works with buttons. These are faster. F1 shows this list.
| Key | Action |
|---|---|
Space |
play / pause |
I / O |
set in / out at the playhead |
Home / End |
jump to in / out |
, / . |
previous / next frame |
Left / Right |
1 s back / forward (Shift = 10 s) |
K |
snap in-point to keyframe |
Z |
reset timeline zoom |
Enter |
trim (lossless) |
D |
Discord MP4 |
G |
GIF |
S |
snapshot |
Ctrl+O |
open (drag & drop and File → Open Recent work too) |
Output names never overwrite anything:
clip_trim_0m14s-0m36s.mp4, clip_discord50mb_0m14s-0m36s.mp4, then
… (2).mp4 if that exists.
Installer (any Windows 10/11 x64 PC): download mp4trim-*-win64.msi
from the Releases page and
run it. It is self-contained: Python, Qt, the Visual C++ runtime and
ffmpeg/ffprobe are all inside, so nothing else needs to be installed.
Per-user install, no admin, Start Menu shortcut; upgrades replace the old
version in place.
- NVIDIA GPU: Discord MP4 encodes on NVENC (fast).
- Any other GPU / no GPU: it automatically uses the x264 CPU encoder. Same size targets, just slower.
- Help → About shows which ffmpeg and encoder it is using.
From source:
pip install PySide6
python fetch_ffmpeg.py # once: downloads ffmpeg into ./ffmpeg
python mp4trim.py [file.mp4]
Without ./ffmpeg it falls back to ffmpeg on PATH
(winget install Gyan.FFmpeg). The app tells you if neither is found.
pip install cx_Freeze
python fetch_ffmpeg.py
python setup.py bdist_msi
The build refuses to run without ./ffmpeg, so an installer can never
ship without it.
These run against real clips (they encode video, so they are not a fast unit suite):
python tests/run_all.py <clip.mp4> # recommended: all suites below, timeouts + summary table (--fast skips the two slow export suites)
python tests/check_exports.py <clip.mp4> ... # every tier: size, codec, audio, duration
python tests/ui_smoke.py <clip.mp4> # drives the window: marks, zoom, export, cancel
python tests/quality_compare.py <clip.mp4> # side-by-side frame + color tags
python tests/check_misc.py <clip.mp4> # GIF ladder, frame-accurate, handles, snapshot
python tests/check_v21.py <clip.mp4> # fine scrubbing, folder nav, OLED theme
python tests/check_glass.py <clip.mp4> # liquid-glass panels: auto-hide, volume, mute, fullscreen
python tests/check_update.py # auto-updater: feed rules, download, UI
python tests/check_tiers.py <clip.mp4> # Discord tier limits on a real clip
python tests/check_scrub.py <clip.mp4> # scrub engine: latency, exactness, cache, UI
python tests/check_portable.py <app_dir> <clip.mp4> # stripped PATH, no NVENC: bundled ffmpeg + x264
python tests/accept_installed.py <clip.mp4> # installed app, real 'D' keypress, checks output
python tests/make_screenshot.py <clip.mp4> # regenerates docs/screenshot.png
mp4trim.py the whole app: UI, playback, export planning, ffmpeg wiring
setup.py cx_Freeze build → exe + MSI
fetch_ffmpeg.py downloads the ffmpeg that the installer bundles
make_icon.py regenerates icon.ico / icon.png
tests/ real-file export checks, UI smoke test, screenshot renderer
docs/ README images