Documentation

Typical workflow

• Drag drop a video file into player or use ⌘/CTRL+O.
• Press SPACE to play/pause or ◀▶, ,. or mouse/trackpad wheel to seek back/forth.
• Set the cut segment’s start and end time by moving the time marker and then pressing I to set start time, and O to set end time. + to create a new segment. If you omit pressing O, a marker will be created instead.
  • Note that all segments you create will be preserved and exported as new files. You can change this behavior with the Yin Yang symbol ☯️, in which case it will instead remove all selected segments and export the parts between segments.
  • Note also that start times will not be accurate, see Known issues
• (optional) If you want to add more than one segment, move to the desired start time and press +, then select the next segment start/end times with I/O.
• (optional) If you want to re-merge all the selected segments into one file after cutting, toggle the button Separate files to Merge cuts.
• (optional) If you want to export to a certain output folder, press the Working dir unset button (default: Input file folder)
• (optional) If you want to change orientation, press the rotation button
• (optional) By default, audio, video and subtitle tracks from the input file will be cut and exported. Press the Tracks button to customise and/or add new tracks from other files.
• (optional) select a new output format
• (optional) In the right-hand segments panel, right click a segment for options, or drag-drop to reorder. Segments will appear in this order in the merged output.
• When done, press the Export button (or E) to show an overview with export options.
• (optional) adjust any export options
• Then press Export again to confirm the export
• Press the Camera button (or C) if you want to take a JPEG/PNG snapshot from the current time
• If you want to move the original file to trash, press the trash button
• For best results you may need to trial and error with another output format (Matroska takes nearly everything), change keyframe cut mode or disable some tracks (see known issues).
• Press SHIFT + / to view and edit all keyboard & mouse shortcuts.
• Note: The original video file will not be modified. Instead, a file is created file in the same directory as the original file with from/to timestamps in the file name.

Primer: Video & audio formats vs. codecs

Here’s a little primer about video and audio formats for those not familiar. A common mistake when dealing with audio and video files, is to confuse formats, codecs, and file names. In short: A file’s media format is a container that holds one or more codecs (audio/video/subtitle) inside of it. For example .mov is a container format, and H265/HEVC is a codec. Some formats support only a few codecs inside of them, while others support more codecs. The most common formats are MP4/MOV (often .mp4,.mov,.m4a) and Matroska (often .mkv,.mka). Example: If you have a file named My video.mp4, this file most likely (but not necessarily) has the format MP4. Note that the extension of a file (in this case .mp4) doesn’t really mean anything, and the file could in reality for example have the MOV format, or the extension could be .txt. Inside My video.mp4 there are multiple tracks/streams, each with their own codec. In this example, let’s say that it contains one H264 track and one AAC track. In LosslessCut you can view and add/delete/modify these tracks.

Remuxing: If you change the output format in LosslessCut and export a file, you are remuxing the tracks/codecs into a different container format. When you do this, the operation is in theory lossless, meaning you will not lose any codec data and the different tracks will remain exactly the same, even though the format is now different (but some format metadata might get lost due to incompatibilities between container formats). There are limitations: Some popular codecs like VP8 or VP9 are not supported in popular formats like MP4, and some popular formats like Matroska (.mkv) are not natively supported in popular video players like iPhone or QuickTime.

If you want to reduce the size of a file using LosslessCut you have to “get rid of” something, either:

• Reduce the duration of the file (cut off start/end)
• Remove one or more tracks/streams (e.g. remove an audio track that you don’t need) Other than that you it’s not possible convert a file losslessly to reduce its size, unless you re-encode and lose quality. For that, I recommend using a different tool like e.g. HandBrake.

Here is a great introduction to audio/video: howvideo.works.

Segments

Segments are the first class citizens of LosslessCut. A segment is a time-slice of your media file, defined by a start time and an end time. When a segment has no end time, it’s called a marker. Segments have a segment number (their export order), and can optionally have a label and tags. Segments are be the basis of what gets exported.

Markers

A segment that has no end time is called a marker. It has no length and will be excluded from exports, but behaves similar to segments. Markers are distinctively visualized on the timeline with a vertical line and a number on top. You can convert markers to segments by setting their out-point (O). This can be done manually or by one of the many tools in LosslessCut. For example you can invert all segments on the timeline to convert all markers into segments.

Tracks

The LosslessCut tracks panel is used to selectively enable/disable individual tracks for export and edit track or file metadata. It can also be used to change content disposition.

Custom exported file names

When exporting segments as files, LosslessCut offers you the ability to specify how the output files will be named in sequence using a template string. The template string is evaluated as a JavaScript template string, so you can use JavaScript syntax inside of it.

The following variables are available in the template to customize the filenames:

Avail. when merging?	Variable	Type	Output
✅	${FILENAME}	string	The original filename without the extension (e.g. Beach Trip for a file named Beach Trip.mp4).
✅	${EXT}	string	The extension of the file (e.g.: .mp4, .mkv).
✅	${EPOCH_MS}	number	Number of milliseconds since epoch (e.g. 1680852771465). Useful to generate a unique file name on every export to prevent accidental overwrite.
✅	${EXPORT_COUNT}	number	Number of exports done since last LosslessCut launch (starts at 1).
	${FILE_EXPORT_COUNT}	number	Number of exports done since last file was opened (starts at 1).
	${SEG_NUM}	string	Segment index, padded string (e.g. 01, 02 or 42).
	${SEG_NUM_INT}	number	Segment index, as an integer (e.g. 1, 2 or 42). Can be used with numeric arithmetics, e.g. ${SEG_NUM_INT+100}.
	${SEG_LABEL}	string	The label of the segment (e.g. Getting Lunch).
	${SEG_SUFFIX}	string	If a label exists for this segment, the label will be used, prepended by -. Otherwise, the segment index prepended by -seg will be used (e.g. -Getting_Lunch, -seg1).
	${CUT_FROM}	string	The timestamp for the beginning of the segment in hh.mm.ss.sss format (e.g. 00.00.27.184).
	${CUT_TO}	string	The timestamp for the ending of the segment in hh.mm.ss.sss format (e.g. 00.00.28.000).
	${SEG_TAGS.XX}	object	Allows you to retrieve the tags for a given segment by name. If a tag is called foo, it can be accessed with ${SEG_TAGS.foo}. Note that if the tag does not exist, it will yield the text undefined. You can work around this as follows: ${SEG_TAGS.foo ?? ''}

Your files must always include at least one unique identifer (such as ${SEG_NUM} or ${CUT_FROM}), and it should end in ${EXT} (or else players might not recognise the files). For instance, to achieve a filename sequence of Beach Trip - 1.mp4, Beach Trip - 2.mp4, Beach Trip - 3.mp4, your format should read ${FILENAME} - ${SEG_NUM}${EXT}. If your template gives at least two duplicate output file names, LosslessCut will revert to using the default template instead.

JavaScript expression tips

Padding numbers

If you need to pad a number, you can use this JavaScript code around the variable. For example to pad the FILE_EXPORT_COUNT variable to 2 digits with leading zeros: ${String(FILE_EXPORT_COUNT).padStart(2, '0')}

If you need more help, you can ask an AI to help you with this, e.g. “How to pad a number with JavaScript?”

Import / export projects

LosslessCut also allows importing/exporting your project (segments) in a variety of file formats. See list of supported formats.

CSV files

• The CSV export/import function takes CSV files with one cut segment on each line. Each line contains three columns: segment start, segment end, label.
• segment start and segment end are expressed in seconds. segment end may be empty, in that case it’s a marker.
• Use comma , to separate the fields (not semicolon ;)

Example .csv file

,56.9568,First segment starting at 0
70,842.33,"Another quoted label"
1234,,Last segment

TSV files

Same as CSV but <tab> instead.

More

• FAQ, known issues, limitations and troubleshooting
• Command line interface (CLI)
• HTTP API