Released in 1995, DVD is a removable storage device. They quickly overtook VHS to become the most popular format for the distribution of video due to their durability (approximately 100 years) and the superior quality of the image. DVD is slowly being overtaken by Blu-Ray which provides a further improvement in terms of quality. Another threat to the sales of DVDs are the rise of online streaming services such as Netflix which allow a user instant access to video with similar or superior picture quality. At its peak several hundred million DVDs were sold yearly.
DVD uses a MPEG-1 or MPEG-2 compression, however MPEG-2 supports higher resolution, up to 720x576 pixels. The DVD format also supports several types of audio including MP2 and Dolby Digital. A DVD may also include subtitles which are stored as bitmap images meaning that any language can be stored as subtitles. DVDs may also contain chapters which allow the user to easily navigate to a specific point in the video. Although not part of the official DVD Video specification, a number of distributors have added copy protection to limit the ease with which a DVD may be ripped and copied.
MP4 files (MPEG-4 Part 14) are multimedia files. MP4 is a container format that can store video, audio and subtitle data (as well as more depending on content). Since stores like iTunes uses this container format, and it is used with iPod and PlayStation Portable (PSP), MP4 files have become more common.
MPEG-4 Part 14 or MP4, formally ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The only official filename extension for MPEG-4 Part 14 files is .mp4.
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