specifying start and end times with ffmpeg

Trying

https://stackoverflow.com/questions/63195747/how-to-specify-start-and-end-frames-when-making-a-video-with-ffmpeg

-ss 00:01:00 == starts at 1 minute

-t 00:01:00 == duration 1 minute

(-start_number when encoding single frame-sequences)

-start_number or -ss has to come before the -i if ffmpeg has to seek without decoding.

putting -t at the beginning, before the input, does not work. 

-t 00:00:10 output.mp4

creates a file with 10 second duration.

but

-ss 00:02:00 -t 00:00:10 output.mp4

Nothing was written into output file, because at least one of its streams received no packets.

Putting -ss at the end of the first -i input.mp4 led to seg fault.

If the input file is properly seekable, this should work to seek to 30 seconds into the video, and get an output which is 10 seconds long starting from that point - 

ffmpeg -ss 30 -i input.mp4 -t 10 -c copy output.mp4

Finishes in milliseconds but won't be frame-accurate due to the -c copy - via https://dev.to/javidjamae/ffmpeg-ss-t-and-to-flags-input-vs-output-seeking-2b3p