We cannot cut between keyframes, it's a technical limitation of modern video codecs. So ffmpeg will choose the nearest keyframe, which will not be the exact time you requested.

Might be able to use avcut for h264 although it is experimental. See #372 (comment)

See also discussion in #13

Update: Have made an initial implementation of this. This experimental feature will re-encode the part of the video from the cutpoint until the next keyframe in order to attempt to make a 100% accurate cut while losslessly copying the rest of the segment.

VideoRedo

VideoRedo is a now-defunct software that had feature overlap with LosslessCut.

• https://www.videohelp.com/software/VideoReDo
• https://forum.videohelp.com/threads/407142-VideoReDo-owner-passed-away-product-ceased-seeking-alternatives#post2668738

Smart Media Cutter

Recently built in order to replace VideoRedo

They open sourced their smart cutting algorithm, could take inspiration from it: https://github.com/skeskinen/smartcut

Remaining issues

Inaccurate seeking

Seeking is not always accurate, causing glitches and/or jumps in the stitch points. This is often because I haven't found a way to consistently seek to and cut on an exact frame. Sometimes it could be caused by the "audio samples" problem below. If you want to experiment, you can try to remove the audio track and cut only video to see if it makes a difference. Another thing to try is to first remux the file to MP4/MOV and then do the smart cut. See #126 (comment)

• How to seek to and cut from a frame in ffmpeg? #1216

Audio samples problem

Cut time accuracy/glitches when audio samples are large? (try without audio and see if it makes a difference). A workaround seems to be to cut audio/video separately and then merge them, with the tradeoff of potential audio/video de-sync:

• Smart Cut - option to cut audio separately in whole, then combine with video result (Request) #1834
• Audio becomes "stretched" around cut from Smart cut only with H264+AAC MP4 files. #2050

subtitles

• Using Smart Cut makes Subtitles unsynchronized  #2049

Other improvements

• rotation sometimes gets messed up Exported video rotates regardless of output settings #2020
• Smart Cut Custom Settings #1824
• If there is no keyframe in a particular segment, re-encode the whole segment instead of erroring with Cannot find any keyframe after the desired start cut point, see #Smart cut failure: "Unable to find keyframe" #1190 (comment)

Done

• Implement a smart cut that re-encodes (lossy) the part between the cutpoint and next keyframe. (done)
• Video quality gets degraded when "smart cutting" (experimental) #1606
• Investigate using aomav1 instead libsvtav1 instead of aomav1 (ffmpeg default) (codec needs to compiled for mac in ffmpeg-build-script) Change smart cut AV1 encoder to libsvtav1 #1825
• custom bit rate SmartCut extreme quality degradation for encoded part due to incorrect detected bitrate from stream #1997

Limitations

• Only works on some files:
  • I've had success with some h264 files, and only a few h265 files seem to work.
  • Other codecs may or may not work.
• Only supports cutting a single video stream (track). All other video streams have to be disabled. We could still probably do multi-passes and then recreate a file with all the streams.
  • Thumbnail stream will be dropped
• We scan up to 60 seconds to find a keyframe.
• It tries to auto-detect bitrate from input stream, however if it fails, then it will calculate bitrate from the whole file's size/duration (may be wrong)
• Tries to copy timebase from source to destination