The new Extract Sub-clip feature sometimes extracts a clip with black screen


#1

I was testing out the new Extract Sub-Clip feature from the new build that came out yesterday and a couple of times already the extracted clip will start with a black screen for the first couple of seconds or so. The audio will still play but with a black screen then after a few seconds the video appears. I tested these faulty clips with both MPC-HC video player and VLC video player.

Also, I noticed that at least on one extracted clip that I played on MPC-HC, when I moved the mouse to the player’s timeline instead of the timer clocking it based on the clip’s duration it was still clocking it based on the original clips duration. So if the clip I extracted came in at 14 minutes or so from the original clip, the timeline on the MPC-HC video player read it from 14 minutes or so rather than from 0. Is that intentional or a bug because it seems to me to be strange behavior. I don’t know if it had anything to do with the fact that the clip I was using had chapter stops but I will note that in case it is a bug and that info could be of some use.


Extracting Sub-clip with white screen
#2

This is very much a your-mileage-may-vary feature due to the nature of the operation (ffmpeg -i input-file -ss __ -to __ -codec copy output-file). If it does not work, then you have to use the re-encode method of Shotcut Export.


#3

I have come across a GitHub page for an app called LosslessCut. In one of its thread a user described an issue with the app that is exactly what I described here while at the same time proposing as a solution to change it so that it cuts at the closest keyframe.

After a bit of lengthy discussion, the lead dev, mifi, posted this as his decided solution

In the newest version 1.13.0 I’ve added a button to the leftmost of the right button row, called nc (normal cut). If you toggle this to kc (keyframe cut) before doing the cut, then it will instead cut at the closest keyframe, -ss before -i , as discussed and suggested by @avh4 , and the output will not contain an empty portion at the beginning of the file. Because I also use -avoid_negative_ts make_zero in that case, audio should be fine

Could this also be implemented to Extract Sub-Clip as a fix?


#4

This change is making the output file report an incorrect duration (much longer). :frowning: Maybe it is better, but I have not yet decided.