[FFmpeg-user] Resuming ffmpeg encode after interrupt

[JD]

When the encoding takes a very long time (> 2 hours), I
often will stop it (^z), syn the FS, suspend the computer to disk (s2d),
and that will power it off.
Now /SOMETIMES/ when I resume, the computer decides to boot as if it was
NOT suspended to disk. This leaves the ffmpeg encode partially done.

So, instead of restarting from the very beginning, is there a way to resume
the encode based on the size of the output file?
I  mean that ffmpeg should be able to know the time offset of the very
last frame encoded. Is this true?
If true, then ffmpeg should be able to continue from the source video file
by starting at the frame (based on the frame's time offset) that follows
the last frame encoded.
I am not an audio video guru. I am just thinking out loud to try to
clarify my question.

Thanx for any help in this.