What is difference between -ss and -itsoffset in ffmpeg?

Question

This is how ffmpeg describes it:

‘-ss position (input/output)’
When used as an input option (before -i), seeks in this input file to position. When used as an output option (before an output filename), decodes but discards input until the timestamps reach position. This is slower, but more accurate.
position may be either in seconds or in hh:mm:ss[.xxx] form.

‘-itsoffset offset (input)’
Set the input time offset in seconds. [-]hh:mm:ss[.xxx] syntax is also supported. The offset is added to the timestamps of the input files. Specifying a positive offset means that the corresponding streams are delayed by offset seconds.

So, what is the difference between the two when both are used as input options? Are they same when -ss is used as input option?

Answer 1

So, what is the difference between the two when both are used as input options?

• The command

  ffmpeg -ss 5 -i inputfile outputfile
  

  discards the first five seconds of input.

  If your input file was 60 seconds long, the output file will be 55 seconds long.

• The command

  ffmpeg -itsoffset 5 -i inputfile outputfile
  

  delays the input file's video streams by 5 seconds.

  If your input file was 60 seconds long, the output file will be 65 seconds long. The first 5 seconds will be a still image (first frame).

• The command

  ffmpeg -itsoffset -5 -i inputfile outputfile
  

  advances the input file's video streams by 5 seconds.

  Similarly to -ss 5, this discards the first five seconds of input. However, if your input file was 60 seconds long, the output file will also be 60 seconds long. The last 5 seconds will be a still image (last frame).

Summing up, -ss crops the input while -itsoffset can be used to sync the video and audio streams.