Input PAL video through non-PAL VCR
June 12, 2006 3:50 PM   Subscribe

Is it possible to get a non-PAL VCR plugged into a Mac Mini to show content from a PAL videotape? Or will I need a PAL VCR?

I realize PAL videotapes become sped up when played through a regular VCR, but is there a simple way to compensate for that with a Mac? I know I can change the display settings so the lines might line up, but is it possible to adjust for the speed?

If it's complicated, then it's not worth it.
posted by destro to Technology (8 answers total)
I didn't think you could play a PAL tape in an NTSC VCR at all. The framerate (25 fps instead of 30) isn't the only problem. PAL is 625 lines, compared to 525 lines for NTSC.

I thought the player would be incapable of synchronizing with the tape. Do you have reason to believe otherwise?
posted by Steven C. Den Beste at 4:23 PM on June 12, 2006

SCDB is right. I've watched PAL tapes played on an NTSC VCR (or possibly dubbed deck-to-deckā€”not sure how they were created) and the results were pretty awful. I mean, you could see what was going on, but all the people had green skin, and there was a lot of static. I suppose in theory there might be some way to apply some kind of reverse distortion, but I've never actually seen it done.
posted by adamrice at 4:27 PM on June 12, 2006

No other reason to think otherwise, just not familiar with video types and assumed it was just a matter of the framerate.
posted by destro at 4:35 PM on June 12, 2006

Most cities have any one of a half dozen groups (and some mail order), that will do a conversion for you.
posted by filmgeek at 4:47 PM on June 12, 2006

Warning. Technical discourse ahead.
There are three main incompatibilities betwixt NTSC and PAL:
1. Framerate. NTSC uses 29.97 Hz interlaced, while PAL uses 25 Hz interlaced. In order to convert framerates, something called "pulldown" is needed to duplicate parts of the frames to match speed.
2. Scan lines. NTSC uses, as SCDB says, 525 lines vertical resolution, whereas PAL uses 625. (usually. There are actually many diffferent varieties of PAL, most of which are incompatible with each other.)
3. Chroma signal. The color information for NTSC is carried on a 3.58 MHz subcarrier, whereas PAL uses a 4.43 MHz color carrier. Quadrature Amplitude Modulation is used to encode hue and saturation data onto the basic luminance signal. PAL adds the additional trick of alternating the phase of the chroma signal on every line. This technique provides correction for phase errors in transmission and gives the system its name, Phase Alternating Line. This is also why PAL looks green on an NTSC screen- the alternating lines confuse the chroma decoder, so it sees the midline average chroma through the whole thing. (Okay, that isn't really entirely it, but it is close enough, isn't it?)

And this is just for the video signal. VCRs are designed for one or the other, and so are optimized for one or the other. PAL VCRs move the tape past the spinning head at 2.339cm/s, while NTSC VCRs move the tape at 3.335cm. This is why PAL tapes look "faster" when played on an NTSC VCR- the frames come at you faster.

So we come to the ultimate answer. This sort of conversion is most assuredly complicated. You would need to figure out exactly what sort of modifications your NTSC VCR is doing to the original PAL signal, then grab the raw but screwy NTSC signal from the VCR and perform the inverse conversion to get a PAL signal which will have large chunks missing from it due to the extremely lossy conversion, then use some heuristics to fill in the signal control data (vert and horiz sync signals) and restack the frames.

It would be much cheaper and easier for you to buy a PAL VCR (about $100) and plug that into your mac. There is also the option of a converting multisystem VCR, ($300 and up) which will play your PAL tapes and generate NTSC output suitable for whatever TV you like.
posted by leapfrog at 5:34 PM on June 12, 2006 [1 favorite]

Later I remembered that PAL also uses a different method of encoding the chroma. Thanks for posting about that.
posted by Steven C. Den Beste at 6:19 PM on June 12, 2006

I remember having a 'GoVideo' mutlisystem VCR back in the 80's. I did a quick search online and found a few systems. The cheapest (so this is the starting point) was a Sony deck at B+H Photo. (I have never shopped there.)

It is not a deck that offers 15 standards, only NTSC and PAL. It is US $194.95.

Don't know if this helps you or not, but the VCR will convert PAL tapes to the NTSC system internal to the VCR. You can this capture the NTSC signal.


It does seem like there would be a Mac based solution here. If a Mac in Europe can capture in PAL, why can't any other Mac? Perhaps it is a software issue. Once it is captured, the conversion will be pretty easy.
posted by Leenie at 8:51 AM on June 13, 2006

"If a Mac in Europe can capture in PAL, why can't any other Mac?" We have no reason to think other Macs cannot. The problem is getting a good signal out of your VCR. The digitizer you use will also need to be able to deal with a PAL signal. Some are designed only for PAL/SECAM or NTSC, but not both.
posted by adamrice at 11:30 AM on June 13, 2006

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