rMux / docs / lossless-trimming-and-in-out-points

Lossless Trimming and In/Out Points

How to trim videos instantly without re-encoding, navigate keyframes with ffprobe, and execute direct stream copies in rMux.

Understanding Lossless Trimming

Modern video codecs (such as H.264 or HEVC packed in MP4, MKV, or MOV) are composed of keyframes (I-Frames) and inter-frames (P-Frames and B-Frames) that encode only pixel motion changes.

Exporting in Lossless Mode:

  • Zero Generation Loss: audio and video streams are copied directly into the new container without decompression cycles.
  • Instantaneous Export: a 2-hour 4K recording trims in mere seconds, bottlenecked only by SSD read and write speeds.
  • Cool & Quiet: zero heavy CPU or GPU rendering load.

Setting In and Out Points

The playback timeline offers frame-accurate scrubbing:

  1. Scrub the Timeline: tap the spacebar to play/pause, or drag the playhead slider.
  2. Set In Point: press I at the start frame of your desired clip.
  3. Set Out Point: press O at the ending boundary.
  4. Step Frames: tap arrow keys ← and → to step single frames forward or backward.

Keyframe Alignment

Lossless trimming requires that video streams begin on a valid Keyframe to prevent visual glitches or frozen opening frames:

  • rMux plots actual keyframe boundaries detected via ffprobe directly on the timeline.
  • If your chosen In point lands on an intermediate delta frame, rMux provides smart keyframe snapping or partial smart-transcoding for opening frames.