Why are HD files so small compared to HQ files?

[Khryz]

Okay, so I've had an EyeTV 250 Plus for about 8 months now and recorded quite a bit of High Quality footage that I would edit in iMovie HD '06 and make PS3 game montages and stuff and put it on YouTube.

A 10 minute HQ movie captured in SD would come out to be about 500 mb once exported to Mpeg-4. I now have the Hauppauge HD-PVR and just captured 6 minutes of 720p HD footage from Warhawk which I edited in iMovie the same, added music, and then exported to Mpeg-4 and it's 210 mb. How is that possible? So if it was 10 minutes it would be still under what my SD movies were?

And a side question - can someone tell me why when I capture a video and it's 500 mb in HD .. when I export it into iMovie HD settings while keeping the same quality the iMovie file is 5 GB?! How is it 10x the size?

 

[CaptainChunk]

1. It's possible that the Hauppauge PVR is using a more lossy codec than your EyeTV did, which would explain the difference in output file size. However, I don't claim to know these devices very well since I normally work with professional video formats.

2. I'm pretty sure that both the Hauppauge and the EyeTV use H.264 compression. iMovie (nor FCE and FCP) will not natively edit H.264 video on the timeline and thus, it needs to convert it into a format that it can work with. So, iMovie trancodes the video into AIC (Apple Intermediate Codec), which has a much higher data rate. Higher data rate = bigger files.