Let’s take a look under the hood of two broadcast VT formats: both are called HDCAM, both do some form of HD, but apart from the operational differences, the funky coloured flap and two extra letters, what is the real difference between them?
Let’s find out.
HDCAM was introduced by Sony ages ago in 1997. No other tape based HD broadcast format was around at the time, and it quickly became clear that one was needed for HDTV to succeed.
The HDW-M2000 machines are based on the DVW-2000 series of VTRs and record with a datarate of 144 Mbps (that’s a 50% increase compared to Digital Betacam’s datarate of 96 Mbps).
HDCAM features 4 audio channels and can handle all common framerates between 24 and 30Fps.
But here’s the snag: a full HD frame is 1920×1080 pixels. To keep the datarate low enough to put this on tape, HDCAM – like its consumer cousin HDV – records frames at 1440×1080 pixels, where each pixel is horizontally squashed and expanded 1.33 times upon playback. The same idea is employed in 16:9 SD signals, where each “square” pixel is stretched 1.78 times to fit the wide screen aspect ratio.
In addition, HDCAM uses the same DCT compression that Digital Betacam uses very successfully. But unlike its predecessor, HDCAM compresses the YUV signal in 3:1:1 rather than 4:2:2. That’s not so good – but again the aim is to keep the datarate low.
Tape stock is essentially the same as Digital Betacam with the same particle density, and the only difference is a bright orange flap and some more holes at the bottom.
In a nutshell: HDCAM doesn’t actually record every detail that the HD-SDI signal potentially has to offer – so a completely new recording format needed to be created. Sticking with the same cassette shells made famous with the introduction of large Betacam SP tapes in 1986, Sony gave us…
HDCAM SR (as in “Superior Resolution”) was introduced 6 years after HDCAM and hit the market in 2003. SR records with a choice of 440 or 880 Mbps, which is over three times as much data as HDCAM.
The format prominently features 12 individual audio tracks and has a built-in Dolby E decoder (i.e. feed it Dolby E as an audio pair, and see the result as decoded single channels if you choose). The SRW-5000 VT machine looks and behaves completely different than its predecessors, which gives you the first impression of a very different beast.
SR’s main advantage is the ability to record the full HD signal “as god made it”: Square 1920×1080 pixels in full 4:2:2, 4:4:4 or even 8:8:8 (it depends on what you feed it; 8:8:8 recording at 880Mbps is achieved by twice the tape speed). Instead of DCT, SR uses the more efficient MPEG4/H264 compression for video (audio is uncompressed).
“Why would I need to record that much data, Jay? Isn’t that a bit overkill?” – Well it depends on your application. If you’re shooting on SR and you’re using it as a replacement for film, then you want to capture everything the HD image sensor has to offer. HDCAM SR can so this for you. SR tapes also come with a pre-attached Tele-File sticker, which contains a 1K memory chip to store meta data about your tape.
12 audio channels give multi-lingual broadcasters a distinct advantage, not to mention less deterioration in post production. At the time of writing it looks like HDCAM is now assumed to be a good TX delivery format, while SR is mainly used at the pre and post production stage.
Even though SR’s tape comes in Betacam cassettes, the particle density is twice as high as in HDCAM and Digital Betacam tape stock. Sony’s official stock brochure states: “We developed particles some 50% smaller than our previous best to capture wavelengths as small as 0.29mm — a human hair can be 300 times wider! The result is incredible performance: two times the output and 2.7 times the recording density of HDCAM tape”.
However, according to usage reports this higher density comes at a cost: minor shocks can cause severe impact on your precious recordings – which is why a new tape box has been introduced with the stock.
Featuring a honeycomb pattern on the inside, sometimes even bubble wrap and tighter locks on the outside. Sony do not recommend for any stock to be re-used. That’s probably not feasible in reality, so beware of dropouts upon re-usage of your stock.
There you have it. Share your own experiences with HDCAM below if you feel like it.
Sources and Further Reading
Wikipedia’s page about the History of Betacam (covers HDCAM and SR)
Forum Post at Creative Cow
Official Sony SRW5000 page (HDCAM SR VTR)
Official Sony HDW-M2000 page (HDCAM VTR)
Official Sony HDCAM SR stock brochure: