I'm processing some videos taken by my dashboard camera and have a couple of questions I'd like to pose.

First question, each video is a maximum of 15 minutes long, but the file sizes can vary from a few hundred MB to a few GB depending on content. I can easily merge these together using ffmpeg or mencoder and codec copying, but is it possible to use ffmpeg or mencoder to *downsample* the video to make it meet a certain filesize? I'm not talking about splitting the video out into chunks (I know ffmpeg at least has a filesize switch or option.) I want to say to ffmpeg/mencoder "here's video x, I want a file of size xxxMB or lower. Do what you can to make it that size or smaller."

Second question, what is the best format to use for streaming over the web (e.g. YouTube/Vimeo) and the best format for local playing? I have so many choices in ffmpeg I'm completely lost about which combination to pick.

For local playing of YT you could make use of youtube-dl which was just recently discussed here.

Thanks, konsolebox, but my second question really was after knowing which combination of codecs was most YouTube/Vimeo friendly after uploading. I wasn't really looking at downloading YT videos.

Nonetheless youtube-dl seems like a nice tool, I might take a look at it.