How to skip start frames with ffmpeg

Question

I have using ffmpeg to create short preview of videos...

$length = $length_video/5;

$ffmpeg_path." -i ".$content." -vf select='lt(mod(t\,".$length.")\,1)',setpts=N/FRAME_RATE/TB -af aselect='lt(mod(t\,".$length.")\,1)',asetpts=N/SR/TB -an ".$content_new.";

Actually this will create 5sec. video. and problem is because first frame is extracted from 0-1 sec.

There is any chance to skip first frame and extract next 5?

Problem is because first frame is actually useless because of video intro

Answer 1

This select filter should skip the first 5 frames:

$ ffmpeg -i input_file -vf select="gte(n\, 5)" ...

For timespan it's even easier. Here's how you skip the first 30 seconds:

$ ffmpeg -i input_file -ss 30 ...

To skip the first 30 seconds and keep the next 120 seconds of the original video, add -t:

$ ffmpeg -t input_file -ss 30 -t 120 ...

-ss  time_off        set the start time offset
-t   duration        record or transcode "duration" seconds of audio/video

Both -ss and -t take a time duration:

The following examples are all valid time duration:

55 55 seconds

12:03:45 12 hours, 03 minutes and 45 seconds

23.189 23.189 seconds

None of these methods will be perfectly accurate due to the very mechanics of how video compression works (P and B frames can not stand on their own). ffmpeg will try to adjust accordingly:

Note that in most formats it is not possible to seek exactly, so ffmpeg will seek to the closest seek point before position. When transcoding and -accurate_seek is enabled (the default), this extra segment between the seek point and position will be decoded and discarded. When doing stream copy or when -noaccurate_seek is used, it will be preserved.

Refer to the ffmpeg documentation for more.