Differences between version 14 and revision by previous author of MPEG.
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| Newer page: | version 14 | Last edited on Thursday, May 3, 2007 1:30:41 pm | by LawrenceDoliveiro | Revert |
| Older page: | version 3 | Last edited on Wednesday, April 21, 2004 11:16:20 am | by JohnMcPherson | Revert |
@@ -1,8 +1,32 @@
-[Acronym] for __M__otion __P__ictures
__E__xpert
__G__roup
+[Acronym] for __M__otion __P__icture
__E__xperts
__G__roup
-Mostly used in reference to
audio/visual [CoDec]s.
+Name for a number of different multimedia container formats and associated
audio/visual [CoDec]s.
-You have almost certainly know about the audio codec "
MPEG 1 layer 3"
, more popularly known as
[MP3
].
+*
MPEG-
1 -- original spec from the early 1990s
, allowing for video at around 320*240 resolution (roughly omparable to VHS quality). Used in Video CD discs, which became quite popular in Asian markets, though they were supplanted by
[DVD
] before they could take off in the West
.
+
+ The spec allowed for three different ways of encoding audio, called layers 1, 2 and 3. MPEG-1 audio layer 3 became very popular in the late 1990s as a way of distributing music on the Internet, because its compression allowed a music piece of several minutes' duration to occupy just a few megabytes, which was tolerable to distribute at dialup speeds while still offering decent audio quality. These files, commonly known as "[MP3]" files, are essentially MPEG-1 files containing audio but no video.
+
+* MPEG-2 extended the MPEG concept to handle a greater variety of resolutions (both low and high) and newer video and audio codecs. MPEG-2 files are commonly found on [DVDVideo] discs.
+
+* MPEG-3 was supposed to be a standard for use in HDTV. It was abandoned when it was realized that these needs could be easily met by either MPEG-2 or MPEG-4. Hence there is no MPEG-3.
+
+* MPEG-4 was apparently based on Apple's QuickTime technology, and includes more interactive features beyond basic audio and video playback.
+
+An MPEG file contains one or more "streams". Thus, video is one stream, and audio is another stream; even if the audio is stereo with two or more channels, that is still one stream. MPEG files on DVD-video discs can contain multiple audio streams for soundtracks in different languages, as well as "private" streams (in formats not defined by the original MPEG specs, but by the DVD-video spec) for holding subtitles and trick-play data. Streams are ''multiplexed'', which means that, as the file is read sequentially, you encounter blocks of data belonging to each stream in turn, which are meant to be played at the same time. This allows a player to process all the streams concurrently, without having to continually jump
+around the file.
+
+!GOP, I-Frame, B-Frame, P-Frame
+Most video codecs rely heavily on ''interframe'' as well as ''intraframe'' compression to reduce data sizes. An ''I-Frame'' is a frame of video compressed by itself, without looking at other frames. However, subsequent frames are quite likely to look similar (think of the common case of something or someone moving against a still background); therefore, instead of compressing them on their own as additional I-Frames, it makes sense to encode them as differences from the ''preceding'' frame (P-Frame), or as differences from ''both'' preceding and following I- or P-frames (B-Frame).
+
+The drawback with this is, if you try to start playback from some arbitrary point that is not at the beginning of the file, the player has to seek backwards until it hits an I-frame before it can start sensibly decoding the video. Thus, using fewer I-frames improves compression, at the expense of quick random access into the video stream. The [DVD-Video|DVDVideo] spec requires at least one I-frame in just over every second of video.
+
+The sequence of frames starting from an I-frame until the last frame before the next I-frame (in other words, containing all the frames depending in some way on the starting I-frame) is called a ''Group of Pictures'' (GOP).
+
+!Licensing
+MPEG-1 doesn't seem to be subject to any licensing requirements. MPEG-2 and MPEG-4 are licensed by [MPEG-LA|http://www.mpegla.com/]. It looks like licensing for MPEG-4 is less onerous than for MPEG-2, if only because Microsoft's Windows Media Player doesn't include support for MPEG-2 or DVD-Video playback, unless you pay for a third-party codec or upgrade to Vista Home Premium or Ultimate.
+
+!See Also
+* lots of info at [mpeg.org|http://www.mpeg.org/MPEG/index.html]
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CategoryStandards
