I'm puting the subtitles in Vegas (video track). I used a letter size that I normally use for subtitles in 4:3 projects: font Arial, letter size 18.
But in the preview window, these subtitles that normally are big enough to be read confortably, become smaller within the 16:9 project! (in other word, the letter size 18 in 4:3 does not have the same value that the letter size 18 in a 16:9 project!)
What must be done to have proper subtitles in a 16:9 project?
How large? Dunno. Try increasing it until it looks the way you want it to in the preview window.
Note that the text entry window is not WYSIWIG and you cannot use it as a judge for text size and placement. It's only an approximation to let you type. You should be looking at the result in the preview window while you're typing to judge what the result will be.
One other possible issue ... is there any chance that you added the subtitle text even to your project while the project settings were 4:3 and then you change the project to 16:9 afterwards? If so then the subtitles are still 4:3. Vegas won't change them to the new project format for you. In that case the text entry window will only be showing you a narrow portion of the video frame so whatever you do there will look bigger than the result in the full 16:9 frame.
It depends -- are you editing in a 16:9 project or a 4:3 project? If you edit in one and render as the other, you may well get graphics/text alignment problems.
Also, if you have a preset graphic or text that you created in a 4:3 project, check to make sure, when you drop it into a 16:9 project, that it's 16:9 and not 4:3. If it's importing as 4:3, then yes, the text is going to appear smaller even though it's supposedly the same point size.
Check the bottom of the preview window where it says Project: [size and framerate] and Preview: [size and framerate]. If the two sizes are not that the same, then your preview is currently being scaled down to fit the size of the preview window. So, yeah, the text is going to appear smaller than it does in the text generator dialog.
If that's the case, go to dropdown box at the top center of the preview window, choose a preview quality (Draft, Good, Preview, or Best) and then Full. The outer areas of the screen will be cut off if your preview window isn't big enough to hold everything, but you will be seeing everything (including the text) at full size. Once you do that, the sizes should look pretty much identical.
Now I have the same proportions in the project and the preview. Thus it means that what I see in the preview windows is going to be the final result on the tape?
In the properties of the text clip > tab Media. Does the option PAL DV Widescreen must be selected when working in 16:9?
I tried that and the subtitle became bigger, and the position of the title in the safe title area of the preview windowis the same than the position of the title in the safe title area of the "placement" tab in the edit text window, although the dimension of the text edit window is 4:3 (720x576) and not 16:9!
Sounds pretty normal. As i mentioned before, the edit window is NOT intended to be a preview. It's just there for you to type in. Watch the preview window while you type to see what it will really look like.
As far as the font size value is concerned, this has no absolute value. It's just a guide that will tell you that in any given frame, choosing 36 will be twice as big as choosing 18. It's not point size since video has no such concept as point size. It's just a relative measure compared to the frame size.
And since it's relative to the frame size, i'll point out that 18 out of 720p is smaller in the frame than 18 out of 480 SD. Since 720 is 50% higher than 480, text of the same size will appear to be only 2/3 as big. Maybe that will explain it for you.
I thought I would test this and this is what I found.
If I make a standard DV AVI project (720 x 480), and make the text size 480. A capital letter almost fills the height of the screen. Thus pretty close to a pixel to pixel relation.
If I make a HD project (1920 x 1080) and create a text size of 480, it also fills the height of the screen. Thus it seems that Vegas is making the size of a font 480 to be close to the height of the video format, regardless of the format resolution.
This would mean that a font size of 18 would fill approximately the same relative height in a standard and HD project.