Lossless Cut Problem

[FL-Artist]

I have been using the Lossless Cut software, and recently I developed an issue. After making cuts to the video the very beginning seems to delay or freeze in the playing startup! you hear the audio but the video is frozen there for a second or two, then it starts playing normally. Anyway of avoiding this issue?

[jagabo]

Cut-in only on keyframes.

[FL-Artist]

Thank You! ...I'm afraid I am somewhat of a beginner to Editing, How do I know when I am cutting on a Keyframe? I researched this after reading your reply, and it sounds very complicated!

[jagabo]

Is this the software you are using?

https://www.videohelp.com/software/LosslessCut

I've never used it but the github page mentions KC vs. NC.

https://github.com/mifi/lossless-cut

[FL-Artist]

Yes I see that! Thanks Jagabo!

[JKyle]

In Lossless Cut, KC puts -ss as an input option in ffmpeg.

But since it is not possible to seek exactly in most formats, ffmpeg will seek to the closest seek point(=keyframe) before position, and puts negative PTS on frames between the keyframe and the cut position in the case of stream copy cut.

This does not cause problems in most players (except mpv), because they skip negative PTS frames and start playing at the cut point. But the nominal running time and the actual running time may be different depending on players.

NC puts -ss as an output option in ffmpeg.

In this case, ffmpeg decodes but discards input until the timestamps reach the cut position.
But since GOP structure is preserved in stream copy cut, this leaves a problem of non-playable frames between the cut point and the first keyframe in the output clip.
Some players just show the first keyframe in place of these non-playable frames. (Maybe this is the issue you're experiencing now.)
Others (ex. mpv) skip them directly to the first keyframe.

Please refer to the ffmpeg manual about -ss option.

[FL-Artist]

Thank You for the reply! this ffmpeg app. has quite a complicated Install I believe, from watching a video on it!

[JKyle]

Lossless Cut is based on FFmpeg and runs it in the background.
You're gonna see a lot of things if you learn about FFmpeg.

[jagabo]

Installing ffmpeg is trivial. But it's a command line driven program and requires a lot of learning.