Specify video thumbnail-frame

[eil]

this is kinda off-topic to XY but i know many smart people are present on this forum so i ask for your knowledge.
how is it determined what frame is taken from video file when thumbnails are formed? is there a way to specify your own?
i don't mean some extra image file to be used, but maybe to add extra frame that i'd wish to see as thumb.
the situation is i have some videos saved with "lesson" how to do some things(say handmade) and the name is not really helpful here, so i'm searching for way to have thumbs just like on youtube before you start to watch - one frame to depict what is video about.

[highend]

After uploading a youtube video you can select one of the thumbnails that google's algorithm created by default / or upload a custom one.
In other words: It's up to the algorithm which thumbnail is used. Most video creating / editing software let you choose an image / a video frame for the video as well

[Marco]

It depends on the thumbnail handler

[eil]

so i download video from youtube, make a screenshot of its preview - how can i make this picture to become a thumb-frame for this file?

[highend]

E.g. http://www.danhinsley.com/index.html
should be able to do it (mp4, mkv and a few others)

Though it's not freeware...

Maybe one of it's alternatives can do it as well (for free?)
http://alternativeto.net/software/metax-for-windows/

Windows Media Player was once able to do that by himself but it lost this feature in the past...

[eil]

thanks for answers, MetaX seems to do it.

[Marco]

http://babelsoft.net/products/mediapreview.htm