Removing frames from a video - how to make playback not pause during removed frames (i.e. assign new timestamps)

Question

I am working off this answer here. I have calibrated my video such that the following code perfectly exports the frames I want to keep

ffmpeg -i in.mp4 -vf "blackframe=amount=0:threshold=92, metadata=select:key='lavfi.blackframe.pblack':value=45:function=less" -vsync 0  img%d.jpg

I modified the code slightly to export to a video

ffmpeg -i in.mp4 -vf "blackframe=amount=0:threshold=92, metadata=select:key='lavfi.blackframe.pblack':value=45:function=less" -vsync 0  outz.mp4

The problem that I face is the output video is the same length as the input. The correct frames are being dropped but I am guessing the timestamp is not being adjusted because the video appears to pause (shows last non dropped frame) during a playback of removed frames.

I guess I could output the image files to another video editor and recompile into a video but I'd like to do this all within ffmpeg if possible.

Thanks!

Answer 1

The easiest way is to retime remaining frames using setpts.

ffmpeg -i in.mp4 -vf "blackframe=amount=0:threshold=92, metadata=select:key='lavfi.blackframe.pblack':value=45:function=less,setpts=N/FR/TB" -vsync 0 outz.mp4