More brainbusters (for me anyway..)

[fmctm1sw]

1] My TV has 480 horizontal lines of resolution. How then can a VCD be 352x240? How does it make up the other 240 lines?

2] What do you need to cap from digital cable?

3] What exactly is a time base corrector and how much does one cost?

4] Why do very few DVD plaers play a mini DVD? Is it not just a DVD that only lasts 15 or 20 minutes? How does my DVD player even know the difference?

5] What exactly happens when a frames drops? I capped a 55 minute VHS tape that dropped well over 10% (probably 25 or 30%) of the frames. The only thing I saw was the audio got out of sync as it went along. I easily corrected this with virtualdub. Nothing was jerky.

[BJ_M]

1. you are getting pixels and lines mixed up 75% of lines = pixels apx
2. someone else can explain
3. Why Do I need a Time Base Corrector (TBC) ?


If you don’t have a video tape recorder (VTR or VCR) you don’t need a time base corrector (TBC). However, you may need a synchronizer, which is commonly confused with a TBC. Definitions and applications of both are explained in this paper.


If you have a VCR you need a TBC. Consumer VCRs may be excluded - unless used for edit or dub/ then a TBC is needed.


Without VCRs, which generate time base errors in television pictures, there would be no need for time base correctors. Put in other terms, if VCRs and video tapes were mechanically perfect, there would be no time base errors to correct -- but like the world and all that is in it, perfect does not exist. TBCs are needed to electronically make television pictures played back from imperfect VCRs and tapes as near perfect (stable) as possible.


What Is Time Base Error?


It is mechanical error or change. In the case of video tape, the errors are introduced by temperature, humidity, drag and tension changes which alter the physical size or shape of the tape at the time of playback versus these same parameters at the time of recording. In the case of the VCR these are errors introduced by mechanical size, shape and condition of the tape path, which changes the physical size and shape of the tape at the time of playback versus these same parameters at the time of recording.


Changes in size or shape of video tape smaller than one thousandth (1/1000 of an inch on a day-by-day VCR to VCR basis is nearly impossible -- electronic control of these mechanical errors in a TBC is nearly perfect.



What Does Time Base Error Look Like?


It manifests itself as geometric distortion in the television picture playback. The most common type of time base error shows up as a bent or curved line in what should be a straight vertical line in the picture monitor (visualize a flag pole with bends in it -- the TBC makes the pole straight again). Sometimes the time base error changes as the tape is played back, causing the bends or curves to change shape or wave back and forth. The top of a picture played back from a VCR is almost always displaced to the right or to the left due to time base error. The TBC removes this displacement.


Do You Need A TBC?

Is Your VCR Perfect?


1. TBCs make clean edits possible by locking the VCRs to the same external sync generator.


2. A sync generator and a synchronizer (SYNC) are two different pieces of electronic equipment.


3. All high quality TBCs have built-in sync generators which reinsert clean H-sync, V-sync and burst on the video signal. For example all Prime Image TBCs have built-in sync generators with clean H-sync, V-sync and burst at both output ports. This is just a side benefit from a TBC that is needed anyway.



4 -- -- someone else can explain
5--- --- frame drop means you lost that frame and it wasnt captured ..

[bugster]

4] Why do very few DVD plaers play a mini DVD? Is it not just a DVD that only lasts 15 or 20 minutes? How does my DVD player even know the difference?

A mini DVD is a DVD file structure and compatible mpeg on a CD. A DVD compatible mpeg can have a data rate of up to 9.8Mbps. Very few DVD players can read data off a CD fast enough to play that video with that kind of data rate. Take a look around the forum for posts about XVCD and XSVCD at high bitrates and see what limits people have found with their players. Data rates of 3Mbps are common. The higher you go the fewer players can cope.

Anothe reason is probably that manufacturerers don't think the potential market for mini DVD playablility is big enough to warrant the extra development and testing required to market such a product.

Hope this helps