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The DVD standard allows a pretty wide variance in quality. From the DVD Video wikipedia entry:

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To record moving pictures DVD-Video utilizes either MPEG-2 compression at up to 9.8 Mbit/s (9800 kbit/s) or MPEG-1 compression at up to 1.856 Mbit/s (1856 kbit/s).

The following formats are allowed for MPEG-2 video:

* At 25 frame/s (used in regions with 50 Hz image scanning frequency):

720 × 576 pixels MPEG-2 (Called full D1)
704 × 576 pixels MPEG-2
352 × 576 pixels MPEG-2 (Called Half-D1, same as the China Video Disc standard)

* At 29.97 or 23.976 frame/s (used in regions with 60 Hz image scanning frequency):

720 × 480 pixels MPEG-2 (Called full D1)
704 × 480 pixels MPEG-2
352 × 480 pixels MPEG-2 (Called Half-D1, same as the China Video Disc standard)

The following formats are allowed for MPEG-1 video:

* 352 × 288 pixels MPEG-1 at 25 frame/s (Same as the VCD Standard)
* 352 × 240 pixels MPEG-1 at 29.97 frame/s (Same as the VCD Standard)

Because of MPEG-1 constraints, interlacing is supported for MPEG-2 video only. All resolutions support video with 4:3 frame aspect ratio. Only formats with 720 pixels per scan line support widescreen video.

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