[mpeg2] Re: docs

[<mocm@convergence.de>]

Kees Cook writes:
 > On Mon, Oct 01, 2001 at 10:45:54AM -0600, Warren Young wrote:
 > > Yes, ANSI has these docs, and they will let _you_ have a copy for about
 > > $400.  That's for the first three sections, which are the main ones. 
 > > (System, video and audio.)  http://webstore.ansi.org/  Search for ISO
 > > 13818, sections 1 through 3.
 > 
 > Gah.  How wonderful to have open standards that cost money.
 > 
 > > For this simple task, you might find a copy of the Mitchell book more
 > > approachable.  It can be had for about $120.  It doesn't replace the
 > > MPEG standards, but it's a whole lot easier to read.
 > 
 > Maybe I can skim it at Barnes and Noble...
 > 
 > > You might do it that way, but usually you chop out the whole GOP,
 > > including the associated I frame.  In other words, while you can leave
 > > an I frame in the stream alone, you usually want to chop whole GOPs out.
 > 
 > Okay, cool.  I was under the impression that the B and P frames might 
 > forward-reference a starting I-frame.  But GOP boundries makes sense.
 > 
 > > > (I realize that it's actually IPBBPBBPBBI.)
 > > 
 > > Actually, that's the playback view.  In the stream itself, the frames
 > > are given as IBBP....
 > 
 > "playback"?  Or decode view?  The _visual_ playback should be IBBP, right?
 > (And, by the way, if the decode view is IPBB, why isn't the stream IPBB?)
 > 
 > > You will also need to know how to parse MPEG-1 audio layer "frames". 
 > > The Mitchell book has almost nothing to say about MPEG audio.  Luckily,
 > > there is a whole lot of free MPEG audio code out there which you could
 > > study.
 > 
 > Agreed.  I have a simple task, IMHO, but I can't do it without format 
 > information.
 > 
 > > For Windows, yes.  Visit the link below and see the MPEG editing article
 > > for info on that subject.  None of the programs mentioned work on Linux,
 > > however, which I assume is your aim since you're posting here.
 > > = MPEG articles: http://tangentsoft.net/video/mpeg/
 > 
 > Ah, yes, this is exactly the kind of article I was looking for.  So, the 
 > formal description is "I want to write a GOP-accurate MPEG editor for 
 > linux."  :)
 > 
 > Now, if I "reverse engineer" the MPEG formats I'm interested in, and
 > "publish" this documentation, will ISO trying to beat me up?  Because I
 > can't believe I'm the only person trying to find details on MPEG file
 > formats.
 > 
 > Thanks!
 > 
 > -- 

I have a primitiv MPEG cutting program in the mpegtools that come with
the DVB card drivers at linuxtv.org. You can give it a filesize and it
will cut the MPEG file along GOP boundaries into the approximate size.
In the code you can see how to find the boundaries. I don't do
anything special for sound, just trusting in good enough muxing :).

Marcus

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Dr. Marcus Metzler                             
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