[FFmpeg-user] Most efficient format/container for seeking

[Maxim E]

Hi,

This question will probably be best answered by developpers themselves, I'm
looking for the most efficient container for seeking.

My problem :
I'm downloading a video file that eventually gets very large, and seeking
can take a lot of time. I guess the whole file is processed until the right
frame is found. Is there any container with which the seeking process is
more "optimized" ?
For instance, instead of processing the whole file, the total duration of
the video is calculated somehow, and the file size is used to look at some
position (if the framerate is constant).

An example to make myself clear :
I've got a 20 Gb file, in a FLV container. No problem to get the total
duration, ffmpeg -i file.flv returns it in just a few seconds (Duration:
55:07:28.35).
No problem when I seek to the beginning of the file, for example "ffmpeg
-ss 00:02:00.00 -i file.flv -t 10 -c:a copy -c:v copy out.flv" gets
executed in a few seconds. However, "ffmpeg -ss 10:02:00.00 -i file.flv -t
10 -c:a copy -c:v copy out.flv" takes at least one minute, which makes me
think ffmpeg process the file from the beginning until it finds the
matching frame.
Let's consider the framerate is constant
20 000 Mo x 10 Hours / 55 Hours should return the approximate position at
which the frame that is sought is, and starting from there instead of
starting from the beginning of the file would make things much more
efficient. Is there such a container that supports this type of seeking ?
Or is it impossible ? I don't have much experience with development/media
files so maybe things are not as easy as I think, but please let me know !

Thank you !