Lossless Video Cutting Explained — What Is -c copy?

Why You Need This

If you have ever trimmed a video and noticed the quality was slightly worse afterward, you experienced the effects of re-encoding. Every encode-decode cycle introduces a small amount of quality loss called generation loss. For archival footage, professional deliverables, or any content where quality matters, this is unacceptable.

Lossless cutting avoids this problem entirely by copying the compressed bitstream from the input file directly to the output file without decoding or re-encoding. In FFmpeg, this is achieved with the -c copy flag, which tells the tool to copy all streams as-is rather than processing them through a codec.

Understanding how lossless cutting works helps you make better decisions about when to use it and when a re-encode is actually necessary. FastCut Pro makes this easy by offering lossless mode as the default and clearly explaining when re-encoding is required for your specific edit.

Step-by-Step Guide

1. Step 1: Open fastcut.cc and load any video file to see lossless cutting in action.
2. Step 2: Set your cut points on the timeline. Notice that FastCut Pro highlights keyframe positions with small markers.
3. Step 3: When your cut point aligns with a keyframe, the cut is perfectly lossless. The green indicator confirms this.
4. Step 4: If your cut point falls between keyframes, FastCut Pro shows a yellow warning. You can either snap to the nearest keyframe for a lossless cut or accept a short re-encode of the frames between the keyframe and your cut point.
5. Step 5: Keep the export mode on Lossless (-c copy). FastCut Pro performs the equivalent of FFmpeg -c copy internally.
6. Step 6: Export the file. Lossless operations complete in under a second even for very large files because no computational encoding is performed.

Why Use FastCut Pro

• No Upload Required — Lossless cutting happens entirely in your browser with no server involvement.
• Lossless Quality — Bitstream copying ensures zero generation loss. The output is identical in quality to the input within the selected range.
• 100% Free — Unlimited lossless cuts with no restrictions. FastCut Pro never adds a watermark.
• Privacy First — Your original high-quality footage is processed locally and never sent to any external service.

Pro Tips

• Most video codecs use a Group of Pictures structure where keyframes appear every one to five seconds. The closer your cut points are to keyframes, the cleaner your lossless cut will be.
• If you frequently need frame-exact cuts between keyframes, consider using smart cut mode which re-encodes only the few frames between the nearest keyframe and your cut point while copying the rest losslessly.
• When working with screen recordings that use constant frame rates and frequent keyframes, lossless cuts are almost always frame-accurate without any re-encoding needed.