[Avamander]

Start uploading a video, pause the upload, you could already get the ID of the vid, render rest of the video and then continue the upload that now contains the ID of the video :D

[vortico]

This is probably it, I'm going to say Bingo.

[techaddict009]

How to pause? and re upload pending part with new video?

[adrianmonk]

Here's a guess: upload from a browser running on Linux, and create a FUSE filesystem that blocks read() calls until you've generated the video.

I tried it with a named pipe ("mknod /tmp/foo.mp4 p") and it gave me an error, but before the error, the web page blocked during upload, but it showed me the URL that will be used (before I gave it a single byte of data).

[zamadatix]

I'm not sure you could do this in the website itself but this would be trivial using the YouTube APIs.

[_nalply]

And then cut away the beginning.