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Opening media files



Or what to do when you have problems opening media files for editing &/or playback...


If a video or audio file won't open or work properly in your choice of software, there are 3 main routes you can take: you can see of the file can be repaired or altered without re-encoding, you can install added software, or you can use other software as a go-between.




You can try repairing/altering the file, often using specialized utilities for that type or format file. You can often find these sorts of tools using Google or Bing, &/or checking videohelp.com, doom9.org, & similar video oriented sites, including their forums. Usually this approach works best when you have a lot of files from the same source, when your choice of software has problems with certain types of files, or when your source is very common. Packets in AC3 audio streams can have extra padding added to keep sync, contain errors, or can simply be written so your software can't read them. Problems with recorded satellite streams in the EU are somewhat common, & there are perhaps more utilities for these files than any others. Sony apps find video-only mpg2 streams difficult -- if you run these files through software to mux them [multiplex --> combine audio & video into one file] with or without an audio file, it adds the data to the file that Sony apps are looking for. Sometimes an app will only open AC3 when it's muxed with a video file, though you're often better off converting it to .wav 1st anyway since editing AC3 is iffy [Womble software can work, but not always, so I tend to reserve it for 5.1 AC3, as editing 6 wav files simultaneously can be a real headache]. Sometimes the solution is simply renaming the file's extension [e.g. .avc to .mp4] -- while that often doesn't work, it's painless to try. It's somewhat rare nowadays, but using another app to open & then save a file without re-encoding, rewrites the video/audio stream & might *correct* whatever you preferred software doesn't like or can't handle. Occasionally an app won't work with a certain decoder -- changing the decoder your system uses, or changing the file's fourcc label, or changing the codec's settings can work [usually you change those settings through the same dialog box you use to set up that codec to encode a file].


* * *


Using an intermediate file or software proxy almost always works, but it can cost you quality & time, involve a learning curve, &/or take up LOTS of hard drive space. Rendering to an intermediate file is the least efficient but simplest way to go, providing you have an app that'll read the file in the 1st place. Since you don't want to lose quality as possible, you want to save this intermediate file in a lossless [or near lossless] format -- you'd want to save an AC3 file as uncompressed .wav rather than mp3. [Note: Microsoft's .wav format can't grow beyond 4 GB, which can be a problem if you convert 5.1. AC3 to multi-channel .wav -- use either 6 mono files, or wav 64 [.w64] instead.] [Note 2: AC3 includes lower volume signals with instructions on how far dialog is below max volume -- 1 result is that converting AC3 to .wav you often have low volume levels with stereo files, high volume with 5.1 -- a 2nd result is that many conversion utilities want to change volume levels for you to compensate, not always the way you'd choose, & they don't always ask your permission.] With video intermediates & proxies paying attention to how colors are stored makes a very big difference -- color conversion can be the biggest reason for any quality loss. It's always good find out how your source stores color data [Google/Bing on the video format used], & try to keep it that way, e.g. try not to convert YUV to RGB if you can help it. Colorspace can also be confusing -- a carry-over from analog broadcast to picture tube [CRT] TVs, there are a number of standards still today with HD... in a nutshell these define how black is black & how white is white. Remapping colors so black becomes darker &/or whites are lighter isn't so much of a problem, but going the other way is -- and too often the software &/or hardware doing color range remapping doesn't tell you it's going to do it, so you have to really keep your eyes open, literally. ;-) VirtualDub, a free, linear, video editing app is extremely popular worldwide -- it won't replace a NLE [Non Linear Editor] like VideoWave, & doesn't try, but there are tasks it does much better/faster than most, including creating [& optionally filtering, cropping, resizing etc] an intermediate .avi file that VideoWave, for example, will be quite happy with. Check out videohelp.com for free, lossless or near lossless codecs to use -- bear in mind that some of the more accurate, lossless codecs like Lagarith aren't as fast as less accurate mjpeg, so encoding an intermediate in V/Dubb will take longer using slower codecs, as will your final encode using your editing or authoring app; the choice is yours whether there's enough quality in your source to justify slower performance. VirtualDub however won't accept all sorts of input files, & that's one place where proxies come in...


Working with media files there are 2 kinds of proxies you'll come across -- placeholder files & frameservers. Software can create a placeholder file that's smaller & easier to edit than the usually HD original, & then when you're done editing, everything you've done is applied to the original. Frameservers are more common, & the most popular, used by enthusiasts & pros worldwide is the open source AviSynth. AviSynth opens your original file, optionally manipulates it, and then feeds that data to your editing software, frame by frame as if you were working with the original itself. If there's a way to open a media file, AviSynth can most always do it. If there's a filtering operation [e.g. removing noise], it can handle it along with providing several methods for re-sizing. To use AviSynth you create a text file containing a script & using the extension .avs -- before the word script scares you off, it can be as simple as "AviSource(Name_Of_File)", & there are free apps that will write &/or edit them for you, though NotePad works just fine most of the time. To use AviSynth, after installing Google &/or Bing on what you want to do including the word AviSynth, & you'll usually (in my experience) find several solutions to choose from. Many

video apps will accept .avs files as if they were actual .avi files, including VirtualDub, but many don't... While it's not an ideal solution [it uses RGB color -- not YUV], another free app called VFAPI can work in tandem with AviSynth to give you a fake .avi file that works in most any application -- AviSynth opens your media file & feeds the data to VFAPI --> VFAPI tells your app that it's an .avi file, & feeds it the data it gets from AviSynth, in most cases in real or close to real-time. For all it's Pros, it comes with 2 Cons: it can get iffy if you want to pass several individual video clips to your editor at the same time, & it's harder to get working in 64 bit Windows [Google/Bing for info, .reg files etc -- you basically have to add VFAPI's default registry entries to the 32 bit section of the Windows 64 registry]. Because HD video in intermediate .avi files using a lossless codec can be HUGE, going the VFAPI route, using the original mpg2 or AVC file can actually be faster & your editor more responsive. I often use AviSynth & VFAPI with HD projects where I want to edit & output different sizes/formats of video... I can edit the simple .avs script to add cropping, re-sizing, de-interlacing etc without changing much of anything in the video editor, so I can edit once, then render HD, DVD, & even video for a hand-held. Yes, video editing software can often do the same thing, but I find the AviSynth/VFAPI route tends to just work better, plus every NLE I've tried [including those >$500] usually takes longer to do a much softer looking re-size.


Now that you know about AviSynth & VFAPI, I'm going to introduce 2 more related, free apps you might want to add to your toolkit: dgmpgdec & dgavcdec. Dgmpgdec includes an app called DGIndex which parses mpg2 streams [files], & creates an index to every frame -- AviSynth or VFAPI can read that index, providing a very accurate way to access mpg2 in video software. It can also demux [split] video & audio tracks, & it can remove pulldown [film's shot at 24 fps, but often needs to be 29.976 fps NTSC. This is handled in mpg2 by adding flags to the file saying which frames to repeat to achieve 29.976 fps without actually adding any frames. It's called pulldown.]. Dgavcdec does the same thing for H264/AVC video -- there's also a pay-ware version that includes nvidia's CUDA hardware acceleration if you use their graphics hardware. So... if you want to open AVC video in your video editor [like VideoWave/MyDVD], & it won't work with the file you've got, you can run that file through dgavcdec to create an index file [how long it takes depends on how fast your PC can read the file, but it's generally around 5 - 10 minutes or so]. Next you'd create a 2 line [2 command] .avs text file. 3rd you'd run that .avs file through VFAPI [takes seconds]. 4th & final step: import the fake .avi file VFAPI created into your app & edit/encode.


* * *


To open or import video &/or audio files in editing software [like VideoWave/MyDVD], or players [like Windows Media Player] your software needs to be able to read the file -- if a file's encoded [compressed], the software you want to open that file with needs to have a decoder available. Editing & player software generally work one of 3 ways: 1) it has it's own built-in decoders that may or may not be available to all Windows software, 2) it may rely on whatever system-wide decoders you have installed, or 3) some combination of both 1 & 2. To get an idea of how it works, or just to see if your system has what it takes to handle a particular type of video/audio file or format, use Graphedt from Microsoft [Google to find it separate from a SDK], or else the newer, similar Graph Studio... go to the File menu & click render media file. [since Graphedt is an app to build these sorts of chains, what I call chains (for clarity) are really called graphs.]


Things to consider before adding a codec [COmpressor / DECompressor]... Video & Audio in Windows are handled by several files, each with their own job to do, & there's always a chance that the chain of files Windows tries to put together to work with those media files can conflict. You need 1 file to recognize & open your video file, a 2nd to split it into audio & video tracks, a 3rd & 4th to decode each ot those tracks individually, & then sometimes several more files before a video file's actually available to be played or shows up on the timeline in your editing app. Adding a Codec, encoder, or decoder often adds competition for each link in that chain, & each link is one more chance for an incompatibility that can break your system. Often software will try several times put this chain or graph together -- the unused files that were opened but didn't work can remain open, right along with whatever app called them, making it harder to diagnose compatibility problems because the files causing it are to some extent hidden [sysinternals, a part of Microsoft has a free app, Process Explorer that can show you which files your video software opens]. It gets worse... Direct Show files [often called filters] used by Windows & some video-related software are ranked. When 2 DS filters can do the same job, the one with the higher rank wins -- get's tried 1st. This rank is not always what it should be, & too often is not what you'd want it set at. Graphstudio & Filmerit let you adjust these rankings, called Merit, but it's neither a fun job nor guaranteed to work, plus it can cause problems with other video apps.


Now that you've been warned, sometimes adding a codec or decoder is your only option -- the thankfully somewhat rare vc1 video format is a great example... the only decent way I've found to open this Windows Media family member is to install a ffdshow "tryout". Ffdshow is a package of several codecs together with a complex set of dialogs to help you control what does what on your system, & recent versions are called "tryouts" -- if you need it & install it make sure you get a current version [today the latest available at videohelp.com has a date of 3/27/10]. Many people have no problems with it what-so-ever, but it has great potential to screw up media handling on your PC/laptop -- it's happened to me & several others, & simply uninstalling can't always reverse changes it's made to your registry etc. When you configure ffdshow, be careful to turn on only what you need, & preferably only install it after a backup.




At any rate, after reading a few threads I though this might help, with apologies in advance where it's over-simplified.



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