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Many digital shooters started with DV video, which hammered the nail in the analog video coffin and democratized video production by dropping the price of capturing very good video from $25,000 (BetaSP camera and deck) to well under $4,000 (Sony DCR VX-2000 and FireWire cable). Another strong feature was that DV was simple; simple to edit, simple to understand and simple to explain.
In the world of high definition video, things get much more complex, with a multitude of very different formats competing for your purchase dollars. Understanding the similarities and differences between these formats is critical to making the correct purchase decision, and as always, the various product camps and their loyalists spew fear, uncertainty and doubt about competitive formats. It’s always an election year when it comes to high definition camera gear. So, in this article, I’ll take a stab at explaining the differences and similarities between some of the more prominent high definition formats.
Tech Specs
There are too many high definition formats to cover exhaustively, but the parameters that I explain should help you navigate the spec sheets of most relevant contenders. Table 1 identifies the formats and features that I’ll focus on, starting with the format’s aspect ratio. I’ll be the first to admit that there are many features that I didn’t consider, including sampling rate, on-camera storage format (tape vs. HDD), container format (MXF vs MPG) and the like. From my view, however, those shown in the table are the most relevant and illustrative for future format comparisons. So, let’s get started.
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Format
DV
HDV
AVCHD
XDCAM HD
DVCPro-HD
AVC-Intra
Aspect ratio
.9/1.2
1.33
Variable to 1:1
Variable to 1:1
1.5
Variable to 1:1
Required Pixels
345,600
1,555,200
2,073,600
2,073,600
1,382,400
2,073,600
Codec
DCT-based
MPEG-2
AVC/H.264
MPEG-2
DCT-based
AVC/H.264
GOP Structure
NA
Long-GOP
Long GOP
Long GOP
I-Frame Only
I-Frame Only
Data rate
25 mbps
25 mbps
Variable up to 24 mbps
Variable up to 35 mbps
100 mbps
100 mbps
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Table 1: Formats and features.
By the term aspect ratio, I mean how the video is stretched during display. Figure 1, a shot of Premiere Pro’s Interpret Footage screen, shows the aspect ratios of many common formats, including DV, HD Anamorphic (which is the same aspect ratio of HDV) and DVCPRO HD, which has an aspect ratio of 1.5. Let’s walk through what this means and you’ll see why it’s important.
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Figure 1. Formats and their aspect ratios.
Figure 2 shows the preview window in Premiere Pro’s Project Pane, illustrating the properties of a video of the front wheel of my trail bicycle shot with the Panasonic AG-HVX200P. As you can see in the small preview window, the wheel looks round, despite being comprised of only 1280 horizontal pixels. That’s because during display, Premiere Pro scales the horizontal pixels by 150%, essentially the same as you could do in Photoshop or another image editor.Again, that’s the significance of the 1.5 shown in parenthesis after the 1280×1080 resolution.
Figure 2. Though displayed at 1920×1080, DVCPROHD/100 video is actually comprised of 1280×1080 pixels.
Want proof? Figure 3 shows a video frame exported from Premiere Pro at its native resolution of 1280×1080, and as you can see, the wheel is oval. These are the pixels actually captured by the Panasonic.
Figure 3. The oval bicycle wheel at its native resolution.
In Figure 4, I’ve expanded the frame by 150% to its intended display resolution of 1920×1080 and the wheel is round. This is the image you would see in your video editor or on your HDTV, which both know to expand DVCPro-HD video out to 150% of horizontal resolution.
Figure 4. The round wheel expanded horizontally by 150%.
Without question, the HVX200P takes absolutely stunning pictures, and Figure 4 looks grand, even after the stretching. Yet intuitively we know that anytime scaling occurs, detail is lost. All things being equal, a camera with an aspect ratio of 1:1, that captures the 1920×1080 image pixel for pixel, should reproduce more accurate detail.
Why does the HVX200P capture 1280×1080 rather than 1920×1080? Probably because Panasonic couldn’t source imaging chips that would capture the native image, pixel for pixel, at the necessary price or size. As you can see in Table 1, however, other formats, including XDCAM HD, AVCHD and AVC-Intra, do or will support true pixel for pixel capture and storage. Again, all other things being equal, these cameras/formats should deliver better detail and resolution than DVCPRO-HD, or HDV for that matter.
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There’s one big caveat, however. Just because the format can store the image pixel for pixel doesn’t mean that the camera can capture the image pixel for pixel. Hence the significance of the Required Pixels line in the features table.
For example, the Sony HDR-FX1 had three CCDs, each with about 1.12 Megapixels, which is insufficient to capture HDV’s 1440×1080 resolution pixel for pixel. This meant that Sony was capturing the image and scaling it up to 1440×1080 for storage, and that those pixels were further scaled up to 1920×1080 resolution during display. In contrast, the XH A1 had 3 imagers capturing 1.67 megapixels each. Thus it came as no surprise that the Canon produced noticeably better detail than the Sony in most tests.
The bottom line is that when shopping for camera gear, identify the aspect ratio used in cameras that you’re considering. Understand that this varies in some standards, like AVCHD, where my fun Panasonic AG-HSC1U captures at 1440×1080, while the newer Sony HDR-SR10 captures at true 1920×1080 resolution. Then be sure to check if the CCD or CMOS imagers on the camera have sufficient pixels to capture the required pixels, pixel for pixel.
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