[Libav-user] Seeking during trimming command takes quite a while

[Carl Eugen Hoyos]

Simon Daniels <simondaniels23 at ...> writes:

> I'm using the -ss and -t flags to trim a section of video out of a
> longer original one. As an example, if the video is 60 minutes long,
> and I want minutes 50-52, ffmpeg takes quite a while to get to that
> point. I'll see something like the following (I know my -ss flag
> values don't exactly match my example)
> 
> Users-MacBook-Pro:ffmpeg-0.10 user$ ./ffmpeg -i "Long GOPRO.MP4"
> -vcodec copy -acodec copy -ss 0:05:10 -t 0:00:30 "output1.mp4"

Your command line asks ffmpeg to decode the complete input file and start
encoding / remuxing after 5:10 (for 30 seconds). The faster (but possibly less
exact) variant is to seek to 5:10 and start decoding there:
ffmpeg -ss 5:10 -i input -vcodec copy -acodec copy out.mp4
(-ss may not always work with -codec copy but I just tested it successfully on a
mov trailer.)

> ffmpeg version 0.10 Copyright (c) 2000-2012 the FFmpeg developers

Completely unrelated to your question:
If you are an end user, you are strongly encouraged to always use latest git
head instead of a release: git head always contains more features and fixes.

Carl Eugen