Trimming a video means removing unwanted footage from the beginning, the end, or both. You set a new start time and a new end time, and everything outside that range is discarded. The result is a shorter version of the original clip containing only the section you want.
The difference between trimming and cutting
Trimming removes footage from the edges of a video. You are always keeping a single continuous segment from the original. Cutting (or splitting) divides a video into multiple separate segments, which is a different operation. Trimming is the right tool when you want one shorter clip from one longer source.
When re-encoding is avoidable
If you only need to trim the start and end of a video without changing the format, codec, or quality, some tools can perform a "stream copy" trim. This copies the compressed video data directly without decoding and re-encoding it. Stream copy trimming is nearly instant and produces zero quality loss.
The catch is that stream copy can only cut on keyframes. Video codecs like H.264 and H.265 store most frames as differences from a previous frame. Only keyframes (also called I-frames) contain a complete image. If your desired start time falls between two keyframes, the tool must either snap to the nearest keyframe (potentially keeping a fraction of a second you wanted removed) or re-encode the segment between the desired start point and the next keyframe.
For most practical purposes, the difference is a fraction of a second. If frame-exact precision is critical, re-encoding the trim is necessary.
When re-encoding is required
Re-encoding happens automatically when you change the format (for example, trimming a MOV and outputting an MP4), change the codec, or request a different resolution or quality level. Re-encoding takes longer than stream copy and introduces a small quality loss, but for a single-generation encode the difference is negligible.
What to keep in mind
Always work from the original source file, not a previously compressed copy. Each re-encode adds a small amount of quality loss. If you trim a video that has already been compressed twice, the output will be noticeably softer than one trimmed from the original.
Check the output file size. Trimming a 60-second section from a 10-minute video should produce a file roughly one-tenth the original size. If the output is unexpectedly large or small, the tool may have applied different encoding settings than the source.
How to trim a video in your browser
The MediaBrew trim tool lets you upload any video, set a start time and end time with frame-level precision, and download the trimmed result. The tool uses FFmpeg WebAssembly and processes everything locally in your browser. No file is uploaded to any server. No account needed, no watermark applied.