I dont think we're in Kansas anymore....

[Kingnog]

Straaaange things are going on around here! Im burning my VCDs normally, and everything is working fine...I play it in my DVD player, they work...BUT! (yes, there's always a "but" somewhere..), BUT! When I fast-forward or rewind, even for a split second, then try to watch from where it stops....AHHHH! The video framerate drops to about 1 per second, and the sound comes in and goes out! And it goes on like this until i finally stop the movie and restart it from the beginning! I highly doubt that this is from my DVD player (although it is a very cheap one, and yes, it supports VCDs) because this happened to my friend, soo. The strangest part, though, is that it doesn't always happen. Sometimes it doesn't do that, sometimes it does....thanks for reading this hugely long thing...can you help?

*me*

[PigOnWing]

Sure. Your MPEG stream is missing GOP headers.

I participated (read: nagged) in quite a long thread regarding GOP files, which I believe also deals a bit with headers. The headers issue was discussed in a previous thread, don't remember exactly which.

Basically, the idea is like this: An MPEG stream is made out of I(ntra) frames, which hold a complete frame data; a P(redicted) frame, which hold only the data changes from the Previous I- or P-frame; and B(idirectional) frames, which hold the differences regarding previous and next frames.

Such a bunch of frames, beginning always with an I-frame, is called a Group Of Pictures, or GOP.

Every GOP can have a 'header', which should be something like saying 'here starts a GOP', or it can not have it (as every I-frame is the beginning of a GOP, it's redundant.

However VCD players needs these GOP headers in order to 'maintain in sync', sometimes with the audio, and sometimes with themselves, whenever you FF/FR/Pause/change tracks. As far as VCDSpec goes, for example, Chapter entry points must be entered only on GOP headers.

You can indeed use an MPG file with which doesn't have GOP headers for VCD, however wheneveer you'll do anything with it besides plain 'play', the results would be unpredictable, mostly dependant on player.


If you're encoding your own MPGs, make sure you use GOP headers for each GOP (in TMPGEnc: Setting ==> GOP Structure ==> Output interval of sequence headers ==> set to '1'). If you're talking about MPGs you've downloaded.... Well, then... er... I dunno.

-- Piggie

[vitualis]

I see you had a run in with KoalaBear...

As usually, his posts are full of his dubious "book knowledge" but he completely lacks any useful knowledge of the real world. On a brief perusal of that thread, he seemed to have argued that lengthening the GOP wouldn't affect the quality of the video clip. I can tell you that it definitely does. It can both worsen and improve the quality of the video (which I believe was your point). It (presumably) depends on the encoder and the actual source material.

For instance, changing the GOP length from 15 to 12 for the Panasonic MPEG encoder under the "PAL VCD" template makes a massive difference in the quality of the resultant clip. Using KoalaBear's logic, "it shouldn't matter". Similarly, one of the regular members here (kwag) has created a number of TMPGEnc templates that feature altered GOP structures. He apparent gets pretty good quality with those too (though I haven't personally tested them).

The actual problem (if I'm not mistaken) is rather the absence or presence of MPEG Sequence Headers rather than GOP headers. GOP headers must exist (otherwise the MPEG would be completely stuffed). MPEG Sequence Headers contain a host of useful information including the timing of the clip as well as the aspect ratio and frame size (I think). It is required for FFW and REW for some players (e.g., Philip) and regular sequence headers are required for entrypoint placement.

MPEG Sequence Headers should optimally be placed BEFORE each GOP header by the encoder. TMPGEnc does this by default if you use the VCD templates.

If your MPEG doesn't have regular MPEG Sequence Headers, you can add them by following the relevent procedure on the following page: http://www.vcdimager.org/guides/chapters.html

Best of luck (I hope this is actually the problem! )

Regards.

[Kingnog]

Wow...ive never had replies that were so long! Thanks, hehe. I bet that is the problem, because:
1. The vcd I created using TMPEnc works fine
2. The vcd I created using DVDx did NOT work fine

So that was probably the problem. I'll try it out next time I have a vcd to burn. Thanks a lot

[PigOnWing]

I see you had a run in with KoalaBear...

A long, long time ago.

he seemed to have argued that lengthening the GOP wouldn't affect the quality of the video clip. I can tell you that it definitely does.

Oh, it's obvious that it does, the question was more reagrding how much and if it's an importatn subject to deal with at all.

I was mainly looking then for a 'rule of thumb', then we both nit-picked on 'when and if and how should that rule-of-thumb be broken' - KoalaBear's statements were more regarding the 'whenever there's a need for an I-frame, the encoder can start a new GOP, regardless of the 'default GOP structure' - and that, by itself, is true.

Still, the rule-of-thumb we (I?) was looking for, is 'what default GOP structure is ideal' - to which the answer is 'about twice a second' = GOP12 in PAL, as you stated, GOP15 in NTSC (TMPGEnc's templates seem to be using GOP15 for both, that's all).

The actual problem (if I'm not mistaken) is rather the absence or presence of MPEG Sequence Headers rather than GOP headers.

Which I assumed are the same thing - I stand corrected.

So to answer the original question - the problem was missing MPEG Sequence Headers.

-- Piggie, still struggling with Seamless VCD/CDDA trouble (yup, that was a shameless plug)

[Kingnog]

Well, since we're here I have another question. This one I am pretty sure it is my DVD player. In the middle of the movie "the Others" (and many others...lol...other movies) it suddenly slows down the framerate or something. Like...it gets stuck on one frame, but the counter keeps going on the dvd player. Then it goes to another random frame a few seconds later...but it doesn't do it if I take out/put back the vcd. Instead, it does it in another location. ahhhH! so many annoying problems!