Unfortunately I have simmilar problem as Peter10.
I downloaded clip from YouTube, using Miro and saving it as mp4, with following parameters:
Data Size: 58.86 MB
Bit Rate: 2.40 Mbps
H.264, 1280 × 720, 25 fps, 2.27 Mbps
MPEG-4 Audio stereo, 44.1 kHz, 128 kbps
I made some changes in iMovie (additional text, transmissions etc) and the I export the movie:
Data Size: 200.43 MB
Bit Rate: 8.18 Mbps
H.264, 1280 × 720, 30.12 fps, 8.07 Mbps
MPEG-4 Audio stereo, 44.1 kHz, 109 kbps
Now I tried to burn it in Roxio 10 on DVD in high definition.
There's no problem with playing the videao on MPEG streamclip, QuickTime player.
But in Tost 10, afetr 6% I have result -18771, even when I make "Save as Disc Image"
"Couldn't complete the last command because there is a problem with the source material".