✂ SimpleMp4Cutter

A simple, clean MP4 cutter and joiner with GUI — powered by ffmpeg and built with Python/tkinter.

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📸 Features

• ✂ Cut Mode — Cut any video by setting a start and end time (precise to milliseconds)
• ⛓ Join Mode — Merge two video files, with optional re-encoding for a seamless join
• 💬 SRT Import Mode — Mux external subtitles into MP4/MKV without re-encoding
• 📐 Ratio Fix Mode — Fix wrong aspect ratio metadata in seconds — no re-encode
• 🎬 Video Preview — Live frame preview with timeline scrubber directly in the app
• ⌨ Keyframe Navigation — Jump between keyframes with ← → arrow keys
• 🖱 Click-to-Jump — Click anywhere on the timeline to jump to that position
• [ IN / OUT ] — Set cut points directly from the timeline, with silent validation (IN always < OUT)
• 🚫 Reset Buttons — Reset start/end times back to defaults with one click
• GPU Encoder Support — Choose between CPU (libx264), NVIDIA (h264_nvenc), AMD (h264_amf) or Intel QuickSync (h264_qsv)
• Inline Progress Bar — Percentage and elapsed time shown in the status bar — no popup window
• 🚫 Cancel Join — Button turns yellow during join and allows cancelling mid-process
• ⏮⏭ Prev/Next Navigation — Browse through all videos in the same folder with Prev/Next buttons
• 📂 Dynamic Path Labels — Long paths are automatically shortened, always showing the filename
• CRF Quality Slider — Control encode quality from 0 (lossless) to 51 (low)
• ✅ ffmpeg Status — Header shows ffmpeg status at a glance — click to set path manually
• Auto-detect ffmpeg — Prompts automatically on first start if ffmpeg is not found
• Window position memory — App reopens exactly where you left it
• Smart file naming — Output files are automatically named _part01, _part02, _joined01 etc. — no overwrites
• Config persistence — All settings saved automatically next to the exe

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🎬 Usage

✂ Cut Mode

Field	Description
Source File	The video you want to cut
Output Folder	Where the cut file is saved
Timeline	Scrub through the video — click anywhere or drag
← →	Jump between keyframes with arrow keys
[ Set IN	Sets start time to current timeline position (only if < OUT)
Set OUT ]	Sets end time to current timeline position (only if > IN)
🚫	Resets start to 00:00:00.000 / clears end time

Time format: HH:MM:SS.mmm or plain seconds like 83.5

Output is saved as originalname_part01.mp4, _part02.mp4, etc.

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⛓ Join Mode

1. Select File 1 and File 2
2. Optionally enable Re-Encode for a seamless join at the cut point
3. Choose your encoder and adjust the CRF slider
4. Hit JOIN FILES — output saves next to File 1 as _joined01.mp4

Encoder Options

Encoder	Requires	Speed	Notes
libx264	CPU only	Slow	Best compatibility, most accurate CRF
h264_nvenc	NVIDIA GPU	Very fast	Requires CUDA driver
h264_amf	AMD GPU	Very fast	Requires AMD drivers
h264_qsv	Intel GPU	Fast	Requires Intel drivers

Note on GPU file size: GPU encoders need a higher CRF value (28–35) to produce similar file sizes as CPU at CRF 23. The quality difference is minimal — GPU encoders are simply more efficient per bit.

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💬 SRT Import Mode

Mux an external subtitle file into a video container — no re-encoding, stream copy only.

1. Select your MP4 source file
2. Select the matching SRT subtitle file
3. Choose a destination folder
4. Configure track names and language codes for audio and subtitle streams
5. Choose output format: MKV (recommended) or MP4
6. Hit SRT MUXEN

Setting	Description
Audio Track Name	Label shown in media players for the audio stream (e.g. DEU, English)
Audio Language	ISO language code embedded in the container metadata
Subtitle Track Name	Label for the subtitle track
Subtitle Language	ISO language code for the subtitle stream
Output Format	MKV supports SRT natively; MP4 converts to mov_text

Output is saved as originalname_muxed.mkv (or .mp4) in the selected folder.

All track settings are saved automatically and restored on next launch.

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📐 Ratio Fix Mode

Fix a wrong aspect ratio flag in the video container — no re-encoding, only the header metadata is rewritten. The video data itself is untouched.

1. Load a source file via the file panel
2. Select the target aspect ratio from the dropdown
3. The preview updates live — showing exactly how the video will look with the new ratio (letterbox / pillarbox simulation)
4. Hit FIX ASPECT RATIO — the button only activates once a ratio is selected and a file is loaded

Available Presets

Preset	Ratio	Use case
Standard HD/4K	16:9	Most modern video
SD / old formats	4:3	Legacy TV, older cameras
Ultrawide	21:9	Widescreen monitors
Cinemascope	2.35:1 (235:100)	Cinema anamorphic
Cinemascope	2.39:1 (239:100)	Cinema anamorphic (DCI)
Flat	1.85:1 (185:100)	Cinema flat
Square	1:1	Instagram, social media
Portrait	9:16	Mobile, TikTok, Reels
Custom	any X:Y	Free input, e.g. 178:100

Output is saved as originalname_arfix01.mp4, _arfix02.mp4, etc.

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⌨ Keyboard Shortcuts

Key	Action
H	Show shortcuts
F1	Switch to Cut mode
F2	Switch to Join mode
F3	Switch to SRT Import mode
F4	Switch to Ratio Fix mode
F5	Cut & Save
F6	Join Files
F7	Fix Aspect Ratio
F8	Mux SRT
S	Browse source file (Cut mode)
O	Browse output folder (Cut mode)
← →	Jump 1 keyframe
Ctrl + ← →	Jump 10 keyframes
Home	Set IN point
End	Set OUT point
PgUp / PgDn	Previous / Next file in folder
1 / 2	Open File 1 / File 2 (Join mode)
R	Toggle Re-Encode (Join mode)
E	Focus encoder dropdown (Join mode)
Q	Focus CRF slider (Join mode)

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⚙️ ffmpeg

The ffmpeg confirmed label in the top-right of the header shows whether ffmpeg is available. Click it to manually select your ffmpeg.exe.

Auto-detect search order:

1. Manually set path
2. System PATH
3. C:\ffmpeg\bin\ffmpeg.exe
4. C:\Program Files\ffmpeg\bin\ffmpeg.exe
5. C:\Program Files (x86)\ffmpeg\bin\ffmpeg.exe

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🗺 Roadmap

Version	Feature
✅v1.0	Basic cut & join GUI
✅v1.1	GPU encoder support, live progress window, English UI
✅v1.2	Video preview, timeline scrubber, IN/OUT markers, keyframe navigation
✅v1.3	Click-to-jump on timeline, ffmpeg auto-prompt on first start
✅v1.4	Window position memory, reset buttons for start/end time
✅v1.5	New warm light blue/orange theme — easier on the eyes
✅v1.6	Inline progress bar, cancel join button, log file, layout & UX polish
✅v1.7	Fix terminal window flashing on Windows, disable logging
✅v1.8	Prev/Next file navigation, dynamic path labels, smaller buttons, new scissors icon
✅v1.9	Compact layout, START/END inline with time fields, clean marker labels
✅v2.0	Final UI modification
✅v2.1	Added SRT Import mode: mux external subtitles into MP4/MKV without re-encoding
✅v2.2	Live aspect ratio preview in Ratio Fix mode (letterbox / pillarbox simulation), color-coded mode button bar
✅v2.3	Shortcuts help (H key), olive color scheme, dynamic window height, fixed window width across all modes
🔜v3.0	Fine-tune cut mode — frame-accurate cut point selection
🔜v4.0	Linux & Mac compatibility

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📁 Project Structure

SimpleMp4Cutter/
├── mp4_cutter.py       # Main application
├── icon.ico            # App icon
├── README.md           # This file
├── .gitattributes      # GitHub language detection fix
├── .gitignore          # Git ignore rules
└── LICENSE             # MIT License

mp4cutter.log and mp4cutter_config.json are created automatically next to the exe and are excluded from git.

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📝 License

MIT License — free to use, modify and share.

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Built with ❤️ and ffmpeg