[FFmpeg-user] ffmpeg video fade in fade out question

[Stuart Foster]

Hi,

I am trying to build a command line that performs the following (all 
values for example):

Fast seek into the video sample 10 seconds, then slow seek for 5 seconds 
giving a start point for my new clip at 15 seconds.
I then wish to have the clip start with 2 seconds of black followed by a 
fade from black of 1 second.
Similarly at the end of the clip I wish to fade to black for 1 second 
followed by 2 seconds of black.
 From the seek point I require my total clip duration to be 20 seconds.

Assuming what I require is possible on a single pass what would be the 
correct values for t1 and t2 in the example give.

 From my experiments the values seem to be dependent on the seek and 
duration parameters but I have not been able determine the exact 
relationship.

Example:

linux ffmpeg version git-2019-06-08-b6ca032

Test.mp4 : Duration: 00:10:00.05, start: 0.000000, bitrate: 280 kb/s

ffmpeg -ss 10.000 -i Test.mp4 -ss 5.000 -t 20.000 -filter_complex 
fade=type=in:duration=1:start_time=t1,fade=type=out:duration=1:start_time=t2 
-y Test.avi

Any suggestions ?

Thanks