On Thu, 29 Mar 2007 16:57:28 -0500, "LaRoux" <hlx@newsgroup.nospam>
wrote:
>If it's divX codec for WMP you want, go to www.divx.com and download the
>divX for windows package. Several components aren't Vista compatible yet but
>the codec is.
The point is Media Player won't accept or stumbles on some codecs even
if they're installed on your system. I can download some files, ask
Media Player to play them and this is what happens:
Example file claims it is AVI
1. Media Player starts up, shows "acquiring codec" in lower left.
2. About 20 seconds later it says "codec acquired".
3. It starts to play the video portion only, not the audio.
Now here's the fun part. What did Media Player just say? It acquired
the codec. So you would think if I click on the file a second time it
would just start to play right? No, it again says acquiring codec,
another 20 seconds goes by, then again it plays just the video
portion. If I repeat this exercise in stupidty ten times then Meida
Player will say "acquiring codec" 10 times each time again going out
on the web looking for another copy of the same codec it already
obviously has and again saying it is "installing" it, but never is it
able to play the audio portion.
Now the funniest part of all is I can open this video file in any one
of my other players and it plays fine, BOTH the audio and video
tracks, and no player except for brain dead Media Player needs to
acquire any new codec off the web.
Lets have even more fun. I open the example file in GSpot. (version
2.70a)Surprise it isn't a AVI like the file pretends, it is a divX
file. Since AVI is a wrapper, Media Player should be smart enough to
read the file header like all my other players do before trying to
play or jumping to conclusions it is a avi file. But alas, we're
talking Microsoft software, which we all know isn't too smart.
Lets look deeper. According to Gspot my system has no less then 6
codecs that can play the video stream in this file. Since Media Player
did play the video portion it obviously used one of these, but
apparently can't remember since it keeps going out to the web to get a
fresh copy every time I ask Media Player to play it.
The real problem with this file is Media Player won't play the audio
track. Let's see if we can figure that out. Well guess what, according
to GSpot it says among other codecs Windows Media audio codec and
other compatable Microsoft audio codecs are already installed. This
obviously must be so since all my other players can play this file
fine accessing these codecs. Why can't Media Player?
Deeper into the rabbit hole:
Gspot has a tool that tests the playing of many kinds of video/audio
files. It will look at your system and see which files should play the
file. Seems simple enough. Gspot says file should play using codecs
already there. What's that? Well, still deeper, if we click on that we
learn the file that drives audio is called msaud32.acm and quartz.dll.
Both of these should be in the Windows system 32 folder. Lets check.
Both are. There are several other files, installed as other codecs, to
avoid getting even more muddy, lets skip those.
Remember GSpot can "render" a audio/video file. Not is the usual sense
as it normally pertains to video editing, but a simpler meaning it
that it can hook to Direct Show routines and attempt to play as if it
was a player. Ok, lets try that. Now we're getting somewhere. GSport
reports "partial render failure, video could be rendered, but audio
could not. Hmm we already knew that, can Gspot tell us more?
You bet. At this screen it just states a memory address with "unknown"
behind it which just means something is preventing Media Player from
playing the audio track.
I don't give up easy, have you noticed?
Gspot has another function called VGS that stands for Visual GOP
Structure. First you need to learn what a GOP is. Still deeper into
the rabbit hole.
GOP is a video term that stands for Group Of Pictures. All compressed
videos are comprised of different kinds of frames. These frames have
different construct. You have 'I' frames, which refer to some intra
frame image, these are based on actual data. Then you have 'P' frames
which are actually predicted images from a construct of a prior actual
('I') video frame that the codec just guesses with and makes a I frame
out of which is a educated guess of what the frame should be which
reduces a lot of duplication and in part is what allows a file to get
compressed. And lastly we have 'B' frames which are similar to P
frames but forward or backward predictions of motion. All very
interesting but beyond the scope of what we're trying to figure out
right now. The point is GSpot shows a visual representation of the
GOPs. The usefullness if this is it should find gaps or corruption if
it exists in a video file.
So does my test file have corruption in it? Yes! The GOP visual shows
several flaws or corrupt frames, all happen to be I frames. This is
likely what is preventing Media Player from playing the audio portion,
since the first frame in this video is one that happens to be corrupt.
Apparently Media Player was able to get over the hump and play the
video track anyway, but failed to play the audio for this reason,
while other players apparently were smart enough to skip over the file
corruption.
So now what? Well it doesn't really matter to me since I have other
"smarter" players. But maybe we can fix it. Since corrupt files are a
fact of life when downloading from the Internet for a whole host of
reasons if helps to have some "repair tools" One such application is
called Video Fixer. This is a class of application that can quickly
scan a file see corrupt or missing segements if the file has been
split and you jointed it, then make a offset adjust so it in effect
rewrites the file skipping over the bumps. So I try that.
Now finally Media Player can play the file, both video and audio.
Linear Mode
