Selecting DVD resolutions

[Riredale]

Bill:

DPI has no relevance to video. It’s a measurement that typically defines the pixel structure on printed documents.

NTSC DVD is comprised of frames of still images measuring 720×480 pixels, with about 30 such frames per second. The raw video at the source is compressed with an encoder using the MPEG2 process and typically the bitrate coming off the DVD ranges from 2 up to about 10 megabits per second. If one works through the math one concludes that a single-layer DVD (which can hold up to 4.38GB of data) can show anywhere from about 1 to about 5 hours of continuous video, based on the bitrate used.

Still photos require only a very low bitrate to look clean and sharp, while rapid motion video (such as something shot while walking or from a moving vehicle) needs a high bitrate. If you use a bitrate lower than the optimum then you’ll see MPEG2 artifacts which impart a “blocky” or “grainy” appearance to the video.

Note that “DPI” never comes into the discussion. That’s a printing term.

In practical terms, one can get typically 90 minutes of excellent-quality video (720×480 pixels) on a single-layer DVD with a typical MPEG2 encoder, and up to about 2 1/2 hours on that same DVD disk if a really excellent (read: expensive) MPEG2 encoder is used.

Hope this helps.

[William Mcqueen]

Thanks for taking time to reply, Riredale. I really appreciate it.

I’m working with someone who constantly talks about “broadcast” quality versus “web quality” in regard to the rendering of animation cells into a movie for DVD or Web, that is, a moving segment of animation of about 30 to 60 seconds. He always talks about rendering to these levels of “dpi” quality (DVD versus Web).

He talks about outputting from MAYA the animation cells at 72dpi for web, and encoding from “broadcast” quality for a DVD in order to achieve a high levels of texture, brightness and colour.

I am much more familiar with the rendering of video images from raw AVI files which are directly from a camcorder through a NLE, but I just can’t understand the relevance to high versus low resolution, e.g web versus DVD as it is expressed by the gentleman. (One requiring much more time for rendering!?)

Thanks for your insight,

Bill in Toronto

[Mike Velte]

Resolution describes the height and width of video or digital images.
Typically video for the web is reduced from NTSC or PAL resolutions to half or smaller. Video for a DVD is full NTSC or PAL resolution.

Broadcast quality is a subjective term describing the quality of the images in the video. Video degrades when compressed into a format other than the acquired format. There is no defined standards for quality.

Things that do not matter;
Rendering time- if it is too long, get a faster PC.

DPI and PPI have no reference to images viewed on a computer monitor or TV or on the web. PPI (pixels per inch) is strictly a printing (on paper) option/setting in an app that deals with images and printing. There are no inches on TVs or monitors…only pixels. 300 PPI is considered the digital equivalent of good quality 35mm film. That translates to 90,000 pixels in every square inch of printing. DPI (dots per inch) is a printer quality setting done in the printer’s Print dialog window. Low quality might be one dot for every pixel…higher quality might be many times that.