Quick Google search found me this
http://www.apple.com/quicktime/technologies/h264/
QuickTime 7 features a state-of-the-art video codec called H.264, which delivers stunning quality at remarkably low data rates. Ratified as part of the MPEG-4 standard (MPEG-4 Part 10), this ultra-efficient technology gives you excellent results across a broad range of bandwidths, from 3G for mobile devices to iChat AV for video conferencing to HD for broadcast and DVD.
Pixar
Massive Quality, Minimal Files
H.264 uses the latest innovations in video compression technology to provide incredible video quality from the smallest amount of video data. This means you see crisp, clear video in
much smaller files, saving you bandwidth and storage costs over previous generations of video codecs. H.264 delivers the same quality as MPEG-2 at a third to half the data rate and up to four times the frame size of MPEG-4 Part 2 at the same data rate. H.264 is truly a sight to behold.
Scalable from 3G to HD and Beyond
H.264 achieves the best-ever compression efficiency for a broad range of applications, such as broadcast, DVD, video conferencing, video-on-demand, streaming and multimedia messaging. And true to its advanced design, H.264 delivers excellent quality across a wide operating range, from 3G to HD and everything in between. Whether you need high-quality video for your mobile phone, iChat, Internet, broadcast or satellite delivery, H.264 provides exceptional performance at impressively low data rates.
No Wait for HD
The impressive efficiency of H.264 makes state-of-the-art video more accessible to more people, enabling you to experience the full quality of HD video on todays computers. With H.264, an Apple Cinema HD Display and a dual Power Mac G5, you can turn your home office into a home theater, complete with gorgeous HD playback.
The New Industry Standard
Already ratified as part of the MPEG-4 standard MPEG-4 Part 10 and the ITU-Ts latest video-conferencing standard, H.264 is now mandatory for the HD-DVD and Blu-ray specifications (the two formats for high-definition DVDs) and ratified in the latest versions of the DVB (Digital Video Broadcasters) and 3GPP (3rd Generation Partnership Project) standards. Numerous broadcast, cable, videoconferencing and consumer electronics companies consider H.264 the video codec of choice for their new products and services. This adoption by a wide variety of open standards means that any company in the world can create devices mobile phones, set-top boxes, DVD players and more that will work seamlessly with QuickTime 7.