📄 advanced video compression - part 2.mht
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Subject: Advanced Video Compression - Part 2
Date: Fri, 2 Nov 2007 12:07:41 +0800
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<HTML><HEAD><TITLE>Advanced Video Compression - Part 2</TITLE>
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<TD>
<H1 align=3Dcenter><FONT size=3D+1><B>Advanced Video Compression - =
Part=20
2<BR></B></FONT><FONT size=3D+1><B>Common Distribution Codecs and=20
Containers</B></FONT></H1>
<P align=3Dright>Continued from the <A=20
=
href=3D"http://www.animemusicvideos.org/guides/avtechbeta/video4.htm">fir=
st=20
page</A>.</P>
<P><FONT size=3D+1><B>II. Containers<BR></B></FONT></P>
<TABLE cellPadding=3D0 width=3D"100%" border=3D0>
<TBODY>
<TR>
<TD vAlign=3Dtop><B>1)</B></TD>
<TD vAlign=3Dtop><B>AVI:</B> Microsoft defined the AVI (Audio =
Video=20
Interleave) container as a special kind of RIFF (Resource=20
Interchange File Format). As a container it had very simple =
design=20
attributes which would, in years to come, reveal all kinds =
of=20
limitations of the format. However, it was able to contain a =
very=20
large amount of video formats by having a Four Character =
Code=20
(FourCC) to define which Codec was used to store the video =
stream.=20
All sorts of clever "hacks" have allowed AVI to do all sorts =
of=20
things that it was never designed to do, such as support =
B-frames.=20
However, the container can only be stretched so far, and =
more=20
advanced codecs like x264 can't reach their full potential =
in the=20
AVI container. Although technically superior containers like =
Matroska exist, AVI remains a strong choice. Editing =
applications=20
often don't even support many newer containers, so AVI is =
likely=20
your best option. For distribution, AVI is one of the more =
popular=20
choices, but has been losing ground to other containers =
lately. All=20
Microsoft windows computers have built-in support for the =
AVI=20
container, and most other systems shouldn't have much =
trouble=20
playing it. This means that in order to view an AVI file, =
you=20
generally only need to worry about having the appropriate =
video and=20
audio codecs installed, wheras with a container like =
Matroska, you=20
must also install support for the container =
itself.<BR><BR></TD></TR>
<TR>
<TD vAlign=3Dtop><B>2)</B></TD>
<TD>
<P><B>MPEG:</B> The MPEG container holds audio and video =
that are=20
compressed with... you guessed it... MPEG. The MPEG standard =
not=20
only defines the MPEG audio and video codecs, but also the =
container=20
that they are stored in. DVDs use a special MPEG container =
called=20
VOB that supports additional features like many audio and =
subtitle=20
streams. <BR><BR></P></TD></TR>
<TR>
<TD vAlign=3Dtop><B>3)</B><BR></TD>
<TD vAlign=3Dtop>
<P><B>Quicktime:</B> While Microsoft defined their rather =
simplistic=20
AVI container, Apple developed a more robust and intricate =
container=20
called Quicktime. During the late 90's the Quicktime =
container=20
became the de-facto standard for movie trailers and other =
types of=20
online video which is designed to be viewed in a web =
browser. Cross=20
compatibility, however, has not always been smooth. Although =
Quicktime is available for many different systems, the =
windows=20
implementations of Quicktime have sometimes been less than=20
desirable. While it's an excellent container, bad =
implementations=20
and invasive software has dogged Quicktime for years. If you =
edit on=20
a Mac, then by all means use this container. If you are =
editing on a=20
Windows machine though, AVI is probably a far better choice. =
For=20
distribution, Quicktime is often highly frowned upon by =
viewers who=20
have Windows.<BR><BR></P></TD></TR>
<TR>
<TD vAlign=3Dtop><B>4)</B><BR></TD>
<TD vAlign=3Dtop>
<P><B>Matroska:</B> This open-source container aims to =
become the=20
standard of multimedia containers, but it still has quite a =
ways to=20
go. Technically, it is a very impressive container that =
offers many=20
interesting features you wont find anywhere else. For the =
purpose of=20
AMVs though, it's not a terribly practical option. For =
editing, you=20
would be hard-pressed to find any serious editing software =
that=20
supports this container. Hopefully this will change in the =
coming=20
years, though. As for distribution, you would probably be =
better=20
served by the AVI or MPEG4 containers. Because additional =
software=20
must be installed in order to play Matroska files, you risk =
having=20
people not being able to figure out how to play your video.=20
<BR><BR></P></TD></TR>
<TR>
<TD vAlign=3Dtop><B>5)</B><BR></TD>
<TD vAlign=3Dtop>
<P><B>MPEG4:</B> The MPEG4 container is based on Apple's =
Quicktime=20
container, and is designed to hold MPEG4 compressed audio =
and video.=20
Technically, it can hold a large variety of different video =
and=20
audio codecs, but if you want your files to comply with the =
MPEG4=20
standard, you should use only the standard MPEG4 video and =
audio=20
codecs. Their are 2 compliant types of video codecs that you =
need to=20
be aware of. MPEG4 ASP (advanced simple profile) codecs, =
such as=20
DivX and XviD, and h.264 (also known as AVC, or Advanced =
Video=20
Coding) codecs, such as x264. The standard MPEG4 audio codec =
is=20
called AAC, though it is also acceptable to use MP3 audio. =
It is=20
usually necessary to download additional software in order =
to play=20
MPEG4 files, but because this is a standard and is gaining =
in=20
popularity, it should have much more widespread support in =
the=20
coming years. <BR><BR></P></TD></TR>
<TR>
<TD vAlign=3Dtop><B>6)</B><BR></TD>
<TD vAlign=3Dtop>
<P><B>Windows Media:</B> This proprietary container is =
designed=20
exclusively for holding Windows Media Audio and Video (WMA =
&=20
WMV). Microsoft created this container because their aging =
AVI=20
container couldn't support all of the features that they =
needed.=20
While it is in many ways technically superior to AVI, it =
doesn't=20
offer nearly the openness and flexibility that AVI does. =
Most=20
Windows users shouldn't have too much trouble playing these =
files,=20
but users on other operating systems or older versions of =
Windows=20
may have difficulty. If you edit using Windows Movie Maker, =
this=20
might be an option for you, but otherwise this probably =
isn't the=20
best choice. <BR><BR></P></TD></TR></TBODY></TABLE>
<P><FONT size=3D+1><B>III. Common Distribution =
Codecs<BR></B></FONT></P>
<TABLE cellPadding=3D0 width=3D"100%" border=3D0>
<TBODY>
<TR>
<TD vAlign=3Dtop><B>1)</B><BR></TD>
<TD vAlign=3Dtop><B>MPEG1</B>=20
<P><B>Origins:</B> Back in the very late 80's, the =
<B>M</B>otion=20
<B>P</B>icture <B>E</B>xperts <B>G</B>roup was trying to =
come up=20
with an open, efficient video compression standard which was =
officially brought into the International Standards =
Organization as=20
ISO/IEC-11172, or more commonly known as MPEG1. The MPEG1 =
standard=20
was designed originally for 1.5MBit/second datarates (i.e. =
1X CD-ROM=20
speed, the 1.5 figure includes audio however) and 352x240=20
resolution, although it is not limited to this.</P>
<P><B>How it Works:</B> MPEG relies heavily on Inter-frame=20
compression. There are 3 different types of frames in the =
MPEG=20
standard - Intraframes (I-frames), Predicate frames =
(P-frames), and=20
Bidirectially-interpolated frames (B-frames). I-frames are=20
essentially the MPEG equivalent of Keyframes - these frames =
have all=20
the data necessary to recreate themselves, i.e. you don't =
need to=20
reference another frame to render an I-frame. P-frames =
reference the=20
previous I or P frame and store the changes in picture. =
B-frames are=20
meant to be very low-bitrate frames, so they reference both =
past and=20
future frames.</P>
<P><B>Benefits:</B> MPEG1 was the codec which made =
distributable=20
digital video happen. MPEG could be streamed, stored on CDs =
- you=20
could do all sorts of stuff with it. Even today it is still =
a very=20
viable compression algorithm. You can play MPEG movies on =
almost=20
anything, from settop players, to PCs, to handhelds running=20
PocketPC! That's pretty darn impressive!</P>
<P><B>Disadvantages:</B> MPEG1 is old, lets make no bones =
about it.=20
It's still darned good, and it beats out everything else in =
terms of=20
compatibility, but in terms of technical quality there are =
much,=20
much better things out there. In order to get a good =
picture, it=20
does require more bits/second than other codecs.</P>
<P><B>Recommendations:</B> MPEG1, while it won't make the =
smallest=20
files, is the KING in terms of compatibility. If you want =
everything=20
under the sun to be able to play your AMVs, distribute in =
352x240=20
MPEG1 files. Otherwise, I'd stay away from =
it.</P><BR></TD></TR>
<TR>
<TD vAlign=3Dtop><B>2)</B></TD>
<TD>
<P><B>MPEG2</B></P>
<P><B>Origins:</B> After the MPEG1 standard was finalized, =
and=20
people started trying to apply it to higher-resolution video =
pictures, there were many flaws in the standard that became=20
apparent. The biggest of these was that MPEG1 could only =
compress=20
progressive-scan images, which meant real TV pictures (which =
were=20
interlaced) were very difficult to compress. MPEG2 was born =
out of=20
the desire to achieve compression of broadcast-quality =
video, and to=20
this end it has succeeded. MPEG2 is used for DVDs, ATSC =
(High=20
Definition Television) broadcasts, Personal Video Recorders =
(such as=20
TiVo), and many other applications. MPEG2 is so versatile =
that while=20
originally it was planned to have an MPEG3 standard for=20
High-Definition TV broadcasts, it turned out that MPEG2 =
scaled in=20
terms of bitrate so that only 1 standard was necessary for =
both=20
Standard and High Definition video.</P>
<P><B>How it Works:</B> MPEG2 is very similar to MPEG1 when =
you look=20
at the surface, although several of the underlying pieces =
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