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Navigating the Video Compression Landscape
Compression technology is a critical element to the file workflow of high-definition video production, and the workflow should be a key factor in deciding which camera you purchase. But each manufacturer uses its own implementation of compression and it is often difficult for layman users to understand what is best for their personal application.
On the professional side, Panasonic promotes AVC-Intra, while Ikegami and Sony employ the MPEG-2 Long GoP format. JVC records directly to an Apple Quicktime format using a 35Mbps MPEG 2 codec. Canon uses a proprietary H.264 codec that is contained in an Apple Quicktime MOV wrapper. The RED One camera uses Redcode RAW, a variable bit rate wavelet codec that allows raw sensor data at resolutions of up to 4096 x 2304.
Fortunately, with the latest versions of the commonly used nonlinear editing systems, most of these formats are natively supported. For most users, it’s simply a matter of plug and play. However, camcorder manufacturers go to great lengths to explain the reasons for their proprietary choices.
For pro applications, Sony and Panasonic—the two main camcorder brands—went in different directions on their choice of codecs. However, video technology moves quickly. Hardware and software is constantly being upgraded to accommodate weaknesses. Last month’s problem has often been solved before you even know it exists.
Sony selected the video compression scheme of MPEG-2 Long GoP—at up to 50 Mbps with full 4:2:2 high definition signals—for what it considers the most mature and balanced video compression scheme available at this time.
Panasonic chose AVC-Intra. Though incompatible with Sony’s format, it is fully compliant with the H.264/MPEG-4 AVC standard and follows the SMPTE RP 2027-2007 recommended practice. AVC-Intra is available in a number of Panasonic’s high-definition P2 card-equipped broadcast cameras.
Both Sony and Panasonic’s compression schemes provide production quality HD video at bit rates more normally associated with electronic news gathering applications, permitting full resolution, 10 bit field capture of high-quality imagery in one piece camera-recorders.
AVC-Intra defines 10-bit intra-frame only compression, which is easy for editing and preserves maximum video quality. Panasonic said it outperforms the older HDV (MPEG-2-based) and DVCPRO HD (DV-based) formats, allowing the codec to maintain better quality at 2x less storage. There are two classes: AVC-Intra 50 at 50 Mbps and AVC-Intra 100 at 100 Mbps.
In a white paper comparing the formats released last December, Sony noted that its MPEG HD files are half the size of comparable AVC-Intra files. It contends that with Apple’s Final Cut Pro (not the latest version released this summer), that AVC-Intra took two times real-time to complete an import while it MPEG HD format was imported 1.5 times faster than real-time.
On average, Sony said, MPEG HD was 36 percent faster than AVC-Intra for file import times on Final Cut Pro. On Avid’s Media Composer, Sony gave MPEG HD a 57 percent import speed advantage.
Sony cited MPEG’s ability to efficiently create high quality clips at a lower bit rate translating into smaller file sizes. AVC-Intra, it said, only makes the file size larger and the file import/export speed slower while penalizing the system with double the data rate. This, Sony claimed, requires more processing in Panasonic cameras and makes the editing more difficult.
Panasonic counter argues that AVC-Intra allows higher quality video using lower bit rates. AVC-Intra 50 is the same quality as DVCPRO HD at half the bit rate (50 Megabits) or substantially higher quality with the full AVC-Intra 100 Megabits (close to HDD5 master quality), Panasonic noted.