Lettboxing maths and TMPEng

[DEmberton]

Hi,

I'm trying to convert an anamorphic WS PAL MPEG2 source to letterboxed NTSC SVCD using TMPEng. TMPEng has the "clip frame" filter. If I go to Arrange Setting, and choose centre custom size, this looks to me what I want to do.

Now the hard bit, what numbers to put in? I want the full width, but what to put in for the height?

The way I figure it w/h = 16/9. So h=w*9/16. For width of 720 this gives 405, which looks kind of right.

But the thing that's confusing me, is that if I was doing a PAL SVCD, I'd get exactly the same result. But that can't be right as PAL is 576 lines high rather than 480. So presumably I need to take into account the pixels not being square?

Okay, to calculate the aspect ratio of the pixels: 720/480 = 4:3, so 1:1 = 720*3/4 = 540 / 480 = 1.125. For PAL, 720/576 = 4:3, so 1:1 = 540/576 = 0.9375.

So for my final result, h=w*9/(aspect*16), which for NTSC = 360, for PAL = 432.

So am I even remotely anywhere near the right ballpark here?

Dave

[DEmberton]

Of course I could just set the source to be 16:9 PAL, set the output to be Full Screen (keep aspect) and let TMPEng work it out. Doh!

Still like to know if I got the calculation right.

Dave

[sterno]

I think that's right, yeah. I know 360 is about right for NTSC, so if you did the PAL calculation the same way it should be too. You can always download FitCD and use its aspect ratio calculator for exact numbers.

[banjazzer]

Of course I could just set the source to be 16:9 PAL, set the output to be Full Screen (keep aspect) and let TMPEng work it out. Doh!

Still like to know if I got the calculation right.

I think Full Screen (keep aspect ratio) is the way to go. However, it will be interesting to see if your calculations are right. When I used the centre custom size option I finally had to multiply my calculated height by 1.4 to get correct aspect ratio! I have no idea why - and nor had anybody else.

[WienieMan]

Anamorphic is not 16:9 it is 2.35:1 or 2.11:1. Try it with those ratios.

[DEmberton]

Anamorphic is not 16:9 it is 2.35:1 or 2.11:1. Try it with those ratios.

Oh, yes it is! Oh, not it isn't. etc.

Anamorphic just means the picture is squashed horizontally when stored, and then unsquashed when played back. Anamorphic WS TV is 16:9 squashed horizontally so it fits into 4:3, and then unsquashed by a WS TV. Movies made at 2.35:1 are typically done anamorphically I believe, which I assume is what you're thinking of.

Dave

[vitualis]

Anamorphic is basically storing a 16:9 DAR movie full frame. There is a flag on the video stream that tells the player "play me back at 16:9 display aspect ratio" so that it ends up looking right rather than everything long and skinny.

2.35:1 movies are actually stored as 16:9 display aspect ratio (i.e., anamorphic) WITH letterboxing as 2.35:1 is not a valid aspect ratio flag.

Regards.

[DJRumpy]

Agreed. 4:3 video is displayed AS IS on a televsion. 16:9 video is compressed on the sides, giving it a 'tall' appearance. The player stretches the video on playback to display the correct aspect ratio. To put 16:9 video into a 4:3 aspect ratio, you have to stretch it to it's full width, and then shrink it to fit in vertically.

Anamorphic WS TV is 16:9 squashed horizontally so it fits into 4:3, and then unsquashed by a WS TV.

This isn't quite accurate. A 16:9 movie, displayed on a 4:3 television, is stretched to it's full display width, and then reduced in overall size so that the entire movie can be viewed, causing additional letterboxing to fill up the vertical area.

This should be what you need. VCD and SVCD do not support 16:9 DARS, so you have to use 4:3 aspect ratio if you want a compliant disc (although my player does play them properly, yours may not, so stick to specs if in doubt). These resolutions are WITHOUT letterboxing (image area only). If you use the chart below, and you have a 2.35 aspect ratio movie, then you should resize your movie (without any letterboxing), to 480x208. Add in letterboxing to get the correct 4:3 aspect ratio.


2.35:1 movies: 480x208

1.85:1 movies: 480x256

1.33:1 movies: 480x368

If you want to try an SVCD with a 16:9 DAR, then try these

2.35:1 movies: 480x360

1.85:1 movies: 480x480

1.33:1 movies: ???