Few newbie questions

[chrisa]

Hi all, looking for little advice.

Today I made an SVCD from old vhs tapes. Captured with adaptec videOH capture. Then changed to mpeg2 using TGMPenc, finally burnt with Nero 6.

When playing in my DVD standalone I find that the audio is ever so slightly out of sync. Also ....it is noticable that the frames are slightly jerky.

The SVCD is full - wonder if that has much to do with it as I read somewhere that the less you put on a disk the better the quality?

Anyway, help on the above would be gratefully recieved, prior to me starting another conversion session.

[ebenton]

You probably dropped too many frames during capture. While frames get dropped, the sound doesn't get dropped to match it, so the picture and the sound get out of sync.
You should probably try recapturing at a slower rate.

[indolikaa]

I would suspect dropped frames as well. Looking at your setup, the USB could be the weak link in the chain, especially if it's USB 1.1.

Cheers to Man U

[ZippyP.]

The SVCD is full - wonder if that has much to do with it as I read somewhere that the less you put on a disk the better the quality?

Definitely not the problem. If you decrease the number of minutes on the disk you may be able to increase the bitrate thereby getting better quality. The bitrate can only be increased up to the max for SVCD of 2520 Kb/s and it doesn't matter if the disk is full or not.

[chrisa]

Thanks for your comments.


Re the frame rate: I currently have it set at 29.970000. I presumed that this was a default for SVCD - and could not be altered? If it can be changed, can you advise what to set it at?

[theDruid]

You probably want to set it for PAL settings - which is 25fps.

Not sure how much difference it will make (although it might stop some of the frame-dropping, as your system won't have to try and capture quite so fast.)

The framerate you've got it set at is more like NTSC setting - and we use PAL here in the UK.

Might be worth having a quick look at the What is section in the top left of this site - just to get some ideas of the different standards and setting for (S)VCD's etc..

cheers,
mcdruid.

[Richard_G]

The incorrect frame rate would explain why your video is jerky. During the encoding an extra 5 frames are added each second. I've done it by accident and encoded a 25 fps PAL file to 29.97fps and couldn't work out what was going on to start with.

The correct settings for PAL (ie UK spec) SVCD should be 480 x 576, 25 frames per second, maximum bitrate (Video + Audio) 2600kbs (I find that using 256kb for the audio and 2300kb for the video works well), mpeg 2.

[Gazorgan]

Captures commonly wander. That is you get 25.012 or 24.983 fps. You need to fix this before you encode or you going to be off seconds at the end. There's an AVI framerate fix tool in the tools section.

[theDruid]

Just to clarify - as you're in a PAL region, you want to both...

... capture at 25fps and encode to 25fps.

The framerate fixing sounds like a good idea for a capture too (do this before you encode your avi to mpg for your SVCD).

[chrisa]

Thank you all so much.

My current capture rate is 29fps. I then stick the captured avi into tmpgenc, which converts to 25fps on its way to mpeg 2. therefore, will change the capture rate to 25fps and see what happens. At least, it should be less work for Tmpgenc to do!

Just one thing though that I am curious about. Surely if the capture is only doing 25fps ....then it is is missing more frames from the VHS signal, and would therefore tend to be more jerky?

[theDruid]

right - I'm not a real expert on this, but I'll tell you what I think!

1. If your source VHS is PAL (which it probably is) then it makes no difference anyway!

2. Encoders have problems converting one framerate to another because they have a load of video that runs at - say - 29.97 - frames per second, and they have to convert this to 25fps.

To do this, they have to discard some of the frames. It's hard to remove nearly 5 frames from every second of the video without this sometimes producing jerkiness - especially in big panning shots etc.. where the movement from frame-to-frame should be smooth, but suddenly there's a frame missing... you get the idea.

However, when you're capturing from VHS to a computer, this is not a direct digital copy. All your PC is trying to do is take snapshots of the video at whatever rate you tell it to.

Even if the tape in the VCR is playing at 29.97fps and you're capturing at 25fps, as long as the picture seems to be moving along smoothly, these snapshots 25 times a second will most likely pick up the smooth movement.

Your PC isn't having to decide which frames to discard, it's just capturing what it sees at regular intervals.

Right - all you experts - please correct me if I'm wrong here.

That's the way I see it anyway!

chrisa - I expect you'll sort your problem out by matching up the capture & encoding framerates.

cheers,
mcdruid.