10. Does the DVD-Video standard work with NTSC, PAL, and SECAM ?
The DVD specification supports the MPEG video information on a DVD disc in one of the two formats required for incompatible television systems: the 525/60 NTSC or 625/50 PAL/SECAM video standard. The program material recorded on a DVD disc can belong to only one of the two video standards, not both. This restriction applies to only one side of the DVD. If a DVD disc is double-sided, the video on one side can be recorded in 525/60 NTSC format, and the video on the other side can be 625/50 PAL. This is because the contents on one side are unrelated to the contents on the opposite side. However, such a disc is rare in production. In general, there are two types of DVD-Video discs commonly known as NTSC DVDs and PAL DVDs.

Most NTSC DVD players can play only NTSC discs. However, most PAL DVD players can play either NTSC or PAL discs. These players have the remote control with the N/P button to let the viewer select the NTSC/PAL video standard manually.

There are three major differences between DVD discs designed for playback on different television systems:

picture dimensions and pixel aspect ratio (720x480 NTSC, 720x576 PAL),
display frame rate (29.97 frames/sec NTSC, 25 frames/sec PAL),
the default audio options (Dolby Digital with NTSC video, MPEG audio with PAL video).
All PAL DVD players can play Dolby Digital audio tracks, but not all NTSC players can play MPEG audio tracks. Even though PAL video format has a lower display frame rate, because of its higher picture resolution, the video contents almost always takes more storage space than what would require for the equivalent the NTSC version.

There are tools to convert video materials from NTSC to PAL video standard, and vice versa. However, the conversion is often done prior to video encoding and DVD authoring. If this process is carried out after the DVD is already finalized, there are a lot of artifacts introduced by the conversion process, due to the "macroblock" and "motion estimation" compression nature of MPEG-2. In a nutshell, conversions between these two incompatible video standards are possible but problematic.

When converting PAL to NTSC video, 576 lines of vertical resolution are downconverted to 480 lines, and frames need to be inserted to go from the 25 frames/second of PAL to the 30 frames/second of NTSC. The resultant video is of less actual resolution than the original source, as information is discarded spatially and made up temporally (timewise).

When converting from NTSC to PAL, 480 lines of vertical resolution have to be extrapolated to 576 lines of resolution, and 30 frames/second have to be downconverted to 25 frames/second. The extrapolation process does not actually add any real picture information to the image. It only makes the picture viewable on a PAL display, and often results in a slightly better-looking footage due to an increase in vertical resolution. The frame rate conversion however results in a loss of temporal resolution, as PAL has a lower frame rate than NTSC.

For video-based material, better results are achieved for the DVD to remain in the same format as the source material.