XDCAM
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XDCAM is an optical disk based professional video system introduced by Sony in 2003. It features include tapeless optical disk recording of DVCAM, MPEG IMX and, in the XDCAM HD variant, HDV video data, as well as MXF metadata and a low resolution AV proxy stream, on a disc similar to a Blu-Ray disc called the Professional Disc, which holds 23.3GB of data. The XDCAM range includes cameras and decks which act as drop-in replacements for traditional VTRs allowing XDCAM discs to be used within a traditional tape-based workflow. Via IEEE 1394 and Ethernet, these decks can also serve as random access computer drives for easy import of the video data files into NLE systems.
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[edit] Compression methods
The XDCAM format uses multiple compression methods : MPEG-2 when recording in MPEG IMX, DV25 when recording in DVCAM and MPEG-4 when recording in a low resolution proxy stream. The XDCAM HD variant of XDCAM records MPEG-2 long GOP at up to 35MBit/s (HQ mode).
Most standard definition XDCAM camcorders can switch from IMX to DVCAM with the flick of a switch, although both DVCAM-only and IMX-only models are available.
MPEG IMX does not use temporal compression, which makes it suitable as an editing format. At 50Mbit/s it offers visual quality that is comparable to Digital Betacam, and is still suitable for many TV productions, primarily ENG, where the practicality of a non-linear format outweighs Digital Beta's superior colour resolution (10-bit vs. IMX's 8-bit) and lower compression ratio, although it is also a very popular choice for Reality Television.
The DVCAM mode allows the user to record twice as much footage and maintains a large compatibility with a large amount of low end NLE's. MPEG IMX can record at a bitrate of 30, 40 or 50 Megabits per second, while DVCAM records at 25Mbit/s. The low resolution proxy is recorded at 1.5Mbit/s with 64 kbit/s for each audio channel. The CIF resolution is used for the proxy recordings.
[edit] Professional Disc
The Professional Disc was chosen by Sony as its medium for professional non-linear video acquisition for a number of reasons outlined in their white-paper Why Sony Adopted Professional Disc.
Essentially the Professional Disc format was deemed to be a suitable, cost effective and easy step forward. The discs are reliable and robust, suitable for field work (something which has previously been a problem with many disc-based systems). Additionally, the cost of media is comparable to existing professional formats.
