Why does FFMPEG different arguments' placement create different mov clips?

I use ffmpeg to cut the first 4 seconds of a mov 14 seconds video file.

This is the command I use (on Ubuntu) to create the new clip:

ffmpeg -i H264_test1_Talkinghead_mov_480x360.mov -ss 0 -t 4 -c copy test_1_seg.mov

Alas, with this command, even though I can hear the audio from the start of the new clip, the video starts showing only from ~1 second.

However, if I change the arguments' order in the command slightly, I can see the video from the start:

ffmpeg -ss 0 -t 4 -i H264_test1_Talkinghead_mov_480x360.mov -c copy test_1_1_seg.mov

1. Any idea why the order of arguments matters?
2. Is that a bug/feature?
3. Can other arguments' placement have impact on ffmpeg output?

The original (14 seconds) file is test.mov
The faulty new clip (first 4 seconds) file is test_1_seg.mov
The correct new clip (first 4 seconds) file is test_1_1_seg.mov

1 Answer

Take a look at the documentation:

The two arguments "-ss" and "-t" serve different purposes if you use it as in input or an output option. Wether of both it is is set if they stand before the "-i" or before the output file.