This is very useful technique i always use to publish video into my Youtube channel. I share some step how i do.
Step 1. Upload your video to your google drive.
Step 2. Now go to google plus setting (https://plus.google.com/settings) and under “Photo & Video” check the “Show Drive photos and videos in your photo library” option.
Step 3. Now go to https://www.youtube.com/upload and on the right hand side, you should see a option to import videos from Google Photos, once youtube import your selected video you can publish it.