Differences between version 6 and predecessor to the previous major change of MPEGTerminology.
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| Newer page: | version 6 | Last edited on Saturday, January 9, 2010 5:58:48 pm | by LawrenceDoliveiro | Revert |
| Older page: | version 5 | Last edited on Saturday, January 9, 2010 2:42:56 pm | by LawrenceDoliveiro | Revert |
@@ -11,5 +11,7 @@
In transport stream format, the PES packets are sliced into small pieces, each of which is carried in a transport-stream packet. This is intended for use in transmission over less-than-fully-reliable channels (e.g. broadcast over the air), where a momentary burst of interference or loss of signal will only lose some transport-stream packets.
In program stream format, PES packets are grouped into ''packs'', each beginning with a ''pack header''. Though calling this a “header” is a bit of a misnomer, since it is effectively a packet in its own right, and in particular it has no length field that includes any following PES packets (the pack effectively extends until the next pack header, or the end of the file/bytestream). The purpose of the [pack header|http://www.mpucoder.com/DVD/packhdr.html] is to 1) contain a more precise clock reference (units of 27MHz instead of 90kHz) and 2) give the decoder some indication of the rate at which it will have to transfer data in order to play the movie.
-Note that there is no special header at the start of an MPEG file/bytestream. This means it is in principle possible to concatenate two or more MPEG files together to achieve a playable result, provided that 1) there are no leftover bytes after the end of the last packet in each file, and 2) the player can cope with any resultant discontinuities in the progression of the PTS.
+Optionally following the pack header, there can be a ''[system header|http://www.mpucoder.com/DVD/sys_hdr.html]''. This specifies such things as how many audio and video streams there are, how much bandwidth they might need, and whether audio and video are in fact synchronized to the system clock. The first pack in the file must have a system header.
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Note that, apart from the requirement for the presence of a system header,
there is no special header at the start of an MPEG file/bytestream. This means it is in principle possible to concatenate two or more MPEG files together to achieve a playable result, provided that 1) there are no leftover bytes after the end of the last packet in each file, and 2) the player can cope with any resultant discontinuities in the progression of the PTS.
