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>> I can see and edit both audio and video separately with these large .mpg files that I rip from DVD. You were saying that you don't get this with mpeg, correct? <<
mpg & mpeg are the same thing. mpg is one of the file extensions used by mpeg files.
just like jpg & jpeg, in fact.
joint picture experts group & motion picture experts group, from whence we get these acronyms, were cross-industry bodies established to define (by a combination of committee & consensus) a series of standards for exchange of media. the jpeg one was reasonably straightforward, though we've still ended up with a few different flavours.
mpeg is another matter. it evolved from m-jpeg (motion jpeg) & differs from it crucially in that motion interpolation is performed to further reduce file size. thus, if there isn't much difference between one frame & the next (i.e. not much movement), only the differences need be encoded.
all this "council" could do meaningfully, given that requirements vary from mobile/broadband right through to digital cinema, was establish a set of fairly rigid guidelines for each version of mpeg, defining how the files were to be constructed, what media elements each could include & so forth. bitrates are left to the user.
mpeg-1 was the first stab at it, & layer-3 of mpeg-1 is the bit that carries the audio. nowadays this is known as mp3.
mpeg-2 was a significant improvement, introducing b & p frames (so that the interpolation amongst frames is bidirectional; the frames have to be sent to the decoder in the wrong order for this to work, which is why mpeg-2 as used for live television broadcasts has so much latency). mpeg-2 is also used for dvd.
does anyone know the difference between m-jpeg & i-frame-only-mpeg-2? :-)
there isn't an mpeg-3 because of the widespread misuse of the abbreviation mp3 to refer to the layer 3 (audio) component of mpeg-1.
mpeg-4 is the latest flavour in serious use, exploiting better compression algorithms that have come along recently, though it has yet to be demonstrated as useful to high-end users.
wm9 rivals it & looks the likelier of the two to be adopted for broadcast.
there are other flavours of mpeg too- 7, 21.... some of these are designed to use media that's already stored in the decoder- bitmaps, fractals & so on- to reconstruct sound & images using a set of instructions that's sent in place of much of the raw data. google away.
ok. enough. back to looping.
duncan/r.m.i. & mtv.
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