[g_airborne]

Most likely you are transcoding the video instead of copying the raw stream. A lot of more complicated stuff requires that but things like trimming can be done the fast way by simply cutting of the irrelevant pieces in the raw encoded data itself which is much faster. It’s kind of a sport to find the exact string of flags that has the correct effect without transcoding :)

The reason it often fails is that ffmpeg can do so many things that any time you are using some curious combination of flag A, B and C is likely that no one else has ever done that and there are some side effects ;)

Anyway, some of it can be avoided by learning how containers en codecs work, what I-frames are and all the other nitty gritty details of the world of video where there is so much to learn!

Here’s a great intro to get started for anyone who got curious: https://github.com/leandromoreira/digital_video_introduction

[bambax]

Yes, copying the raw stream is the way to go if you're not rescaling, etc. This is the command to extract 15 seconds of video starting at the first minute, and not reencoding; it should be quite fast and it's also quite self-explanatory:

    ffmpeg -ss 00:01:00 -i in.mp4 -t 00:00:15 -c copy out.mp4

I'm really no expert so I just keep a few of those commands around... You don't need a deep understanding of video streams, etc. just to use ffmpeg.

[cyborgx7]

This is the biggest weakness of ffmpeg, in my opinion.

It oftentimes requires so much understanding of how things actually work, and has too little to offer in the way of abstracting those things away.