Maybe so, but we soon run into codec-related issues.
Windows Media Player opens and plays
the uncompressed AVI file fine. The WMV file is heard but not seen. I
didn't find any tool on my XP computer that could play the video portion of the
uncompressed wmv file.
Movie Maker 2.1 imports, previews and uses the uncompressed AVI
file.
... but it doesn't know how to handle
an uncompressed WMV file, even though it just finished making
it.
It's surely related to codecs, but in this
case it's in the programming of Movie Maker, not in how the codecs are working
or not.
When Movie Maker opens a WMV file it checks to see
what codec it should use.. It considers the option of having
an uncompressed AVI file, but not an uncompressed WMV.
On my Vista Ultimate SP1 system, the uncompressed
WMV plays completely but not smoothly in Windows Media Player, and imports
into Movie Maker 6... where it goes through the motions of playing but
isn't seen or heard when previewing in the collection or on the
timeline.
DV-AVI files
I keep mulling over how to categorize them. At the
moment I consider them 'losslessly compressed'... obviously much
smaller than uncompressed AVI or WMV files.... and maintaining their original
quality through as many editing generations as I want to take
them.
Movie Maker 1 makes type II DV-AVI files, while MM2
and higher make type I. The type II files are a bit larger in file size as
they have an extra audio track.
I used to think all DV-AVI files were the same...
until I started using the Panasonic and Canopus DV codecs in addition to the
Microsoft one that comes with Windows.
-
DV-AVI files made by Movie Maker 2.1 have
some frame dropping issues I don't see when using the Panasonic codec with
other software. I don't know if it's Movie Maker or a codec
issue.
-
The Panasonic codec can't be used by Movie Maker
and the Microsoft DV codec can't be used by VirtualDub. There
are jurisdictional turfs that codecs need to respect. I use what works in the
software I'm using, preferring to work each phase of a project
using DV-AVI files.
-
Apple DV files have MOV
extensions... equivalent to the DV-AVI files of Windows
-
When using the Canopus DV codec
in VirtualDub, the rendered file has the name 'Canopus' on each
frame. It's another jurisdictional thing. Canopus permits their DV codec
to be used only by Canopus software.
DV-AVI files are 'frame-based'. All info about
each frame is self-contained in the file... it reminds me of my
old film-based videos, where each frame was self-contained. I
could see the analog frames with a magnifying glass, each one being a
little picture. I can see each digital frame, but they look like
computer code rather than little pictures.
The compression codec makes the video
file.... packing it with code ready for any decompression codec that
wants to try putting the pieces back together in a viewable way.
Opening a DV-AVI file
The decompression codec
reads the code in the video file and translates it into smoothly
playing frames. If one codec can't do it right, then another might. The
packaging and the unpacking obviously needs to be coordinated. Sometimes
your system doesn't have a codec that can read the code, and sometimes
it does a poor job of trying... and you have an issue
related to codecs.
To play a DV-AVI file, I can
-
right click the file name and use 'Open with'... I'm not sure how the
choices are put into the list, which includes apps I've opened such files with
before. It can't be decided by Windows as it wouldn't include Notepad,
something I use lots.
Running down my current list, the DV-AVI
file...
-
plays fine in Windows Media
Player
-
gets an error message trying to open Windows Live
Photo Gallery, and Windows closes the app on me... but the same file
opens and plays in the Gallery when I open the Gallery first, followed by
the file.... it can't be a codec issue
-
plays at very low ugly visual quality...
all pixilated... in the Quick Time Player
-
opens fine in Notepad!!!! this
is where I'm heading for this exercise... yes it opens, but not being a video
player, Notepad can show the code but not piece it together
-
looks and plays great in VirtualDub
-
Movie Maker opens but says the file isn't a
valid project file... we know that
-
the Camtasia player gives an error message saying
DV-AVI files are currently not supported
-
works fine in the tiny GSpot player shown
here
a DV-AVI file in Notepad
Notepad is on the list because I sometimes use it
to look at video files. Not being a programmer, it's just a bunch of code to
me... but liking puzzles, I enjoy hacking information that I don't yet
understand.
It starts with a section of code I'll
call the file header. The first tidbit of data
says RIFF.
The link takes you to a Wikipedia page that says it stands for Resource
Interchange File Format, a format for storing data in chunks. RIFF was
introduced by Microsoft in 1991. The page says the
first four bytes of a correctly-formatted RIFF file will spell out "R", "I",
"F", "F". This one does.
I don't want to go too deeply into what I don't
understand. Hopefully just enough to help you understand codecs
in general.
After the header comes lots of white space followed
by this section. The Wiki page says: Two chunk identifiers, "RIFF" and
"LIST", introduce a chunk that can contain subchunks. Here's the beginning
of the LIST section.
After more white stuff comes the code
for the individual frames. The sample file has only blackness at the
beginning as the title fades in so the code for the beginning of this first
frame is what's needed to color the frame black.
Jumping to the part of the title clip
that is blackness with a little white lettering looks similar... and
it should as the frames are mostly still black.
The bridge clip is more complex... here's the end
of one frame and the beginning of the next at about the mid-point of the
scene that shows the Golden Gate. The only thing I understand
when looking at the code this way is the line between
frames... that's the place I used to cut at when using a razor
blade to edit film.
One more snapshot... what does the end of the
file look like? It's an index to each of the frames (or half-frames as
DV-AVI files are interlaced).
When I get a DV-AVI file that has problems I check
to see if the index section is there... if not, the file is incomplete and can't
be used. The decompressor has to use the index to recreate the file. A file
missing an index can't be played.
VirtualDub has a feature to rebuild the index
of an AVI file with missing frames or index. Movie Maker doesn't have
such a feature.
That's a peek into the code of this 5
second DV-AVI file.
a WMV file in
Notepad
Different file types and codecs
use different code... the best WMV choice for my computer opens with
this code... no RIFF up front and no index at the end.
It's different coding.
Here's the header of the uncompressed WMV
file... in case you want to compare it to the compressed one.
Conclusion and Closing... and What's
Next?
Most users don't care why or how codecs work. They
just want to easily make, edit and watch videos. When they run into an
issue related to codecs, someone else can and will resolve it for them. If not,
then it's time to make some popcorn and turn on the TV.
I'm glad my subscriber base is mostly of experienced
users.
I thought that by keeping things on the surfacy level,
I'd have room to get into at least an introduction to lossy
compression, but I didn't make it. When exploring the nooks and crannies of
video I always end up with two more questions for each one answered.
A couple new questions are...
-
why is an uncompressed AVI file just about exactly double the
file size of uncompressed WMV? Is it because I started with DV-AVI which
is interlaced, which means it is two half-frames for each frame, while WMV
files are deinterlaced?
-
what happened in Vista so the uncompressed WMV file plays in
the same version of WMP as on my XP system, and imports into Movie Maker
6?
Have a great week....
PapaJohn
For the uncompressed AVI file made by
VirtualDub, GSpot provides some video codec info and says 'No
Codec Required'. 
For the uncompressed WMV file, GSpot provides
different video codec info, and also says 'No Codec Required'.
