How does a codec make itself available to windows

[Panash]

Obvious answer, through the registry, I know.

What's the special name for it? VFW? Direct Show? Does someone know of a tutorial site for all this?

What I'm leading up to is capturing from Vdub, listed encoders include things like the huffy encoder & the PICvideo mjpeg codec if you install it. What is the interface between these. Is there a MPEG encoder that will plug into this interface for capture? (I'm not refering to frameserving here)

PN

[iantri]

Due to Microsoft's insistance on changing standards every few years, there are two standards in use for video capture codecs:

1. Video for Windows (VFW, for the video capture and codecs) and Audio Compression Manager (ACM, for the audio). This is the combination that Virtualdub, AVI_IO and other older software use. This system has some.. issues.

2. Windows Driver Model (WDM, for the capture), and Directshow (for the video and audio encoding/decoding. Under DirectShow, codecs are called filters, technically). This is the new system that VirtualVCR and iuVCR, among others, use. This system also has.. issues.. namely complexity.

(In fact, video capture under Windows is a horrible trainwreck, but let's not go there..)

AFAIK, Video for Windows codecs are not registered in the registry (it is a legacy system that goes all the way back to Windows 3.1), but this may have changed in later versions.

This is all a moot point, however, because you simply cannot capture MPEG video with Virtualdub, or any other AVI capture program.

Why? Because the AVI file structure is fundamentally different from the MPEG elementary/program stream file structure, and proper MPEG data can not be stuffed into an AVI file, as AVI lacks many of the features the MPEG files structures have.

However, if you want to capture directly do MPEG there are three options:

1. Buy a hardware MPEG encoder, such as a Hauppage PVR-250.
2. If you have an ATI All-in-Wonder card, use ATI MMC to do the capture.
3. MainConcept's MPEG encoder has a capture mode that allows you to capture straight to MPEG. (BEWARE!! This requries HUGE amounts of CPU power to do in software.. 2ghz CPU MINIMUM.)

Using ATI MMC (if applicable) or MainConcept's MPEG encoder bypass the normal Windows codec system.

[Panash]

iantri,

just back from hols, read your reply, brilliant answer - exactly what I wanted.

I take it that the Mainconcept benchmark you quoted is for full D1 resolution & there will be some sort of 'area' dependant scaling for VCD?

How well does it do for lip-sync? (there is a modification for vdub that actually uses polynomial resampling if the input framerate is not exactly true to spec, ie from a slow running VCR, to achieve the correct number of audio samples within each frame)

PN

[iantri]

Alright.. I admit.. I made up those system requirements.

I don't use Mainconcept; looking into it a bit further I see now that the capture stuff is indeed a seperate product called Mainconcept PVR. It is cheap (USD$34.90). They list the minimum requirement as an 800mhz CPU. I'd imagine this is for 352x240/288 capture.. 2ghz is not an unrealistic requirement, though, for full-res. 720x480/576 capture, as CCE on my 2.6ghz Celeron can do that at about 1.75 to 2 times real-time. Considering that Mainconcept is slower and capturing is taxing on the CPU, you might squeak by with a 2ghz CPU.

According to its tool page on Videohelp, some people have issues with it. Try the demo. I don't know how it does with audio sync. It probably just drops frames when necessary to maintain sync. If your equipment is OK, you should get at most a few drops an hour. I've had nothing but trouble with software that dynamically resamples (depending on method, audio can lag with many drops, etc.). Either way, I believe that is absolutely inexcusable for a program to lose sync no matter what method is used.

You could also look into other realtime MPEG capture software (usually PVR apps do this), but there is a quality tradeoff or size predictability problem since realtime capture MUST be CBR or CQ mode.

Also, since I first responded I heard about a "codec" called YMPEG. What it cleverly does is pretend to be a regular codec, but doesn't actually produce output. What happens is that you select it in, say, Virtualdub, and capture. You will end up with an empty AVI file, but in real-time YMPEG will create an MPEG file for you.

It is cheap, but some people appearantly have problems with it. The quality is not too great. Check the link above.

EDIT: I was mistaken again. Appearantly, Mainconcept Encoder does have a capture mode. I'm not sure what the difference is. I'm downloading the trial now.

Good luck.
iantri