Video Tutorial 1

This is first part of tutorial to help you capturing, editing, creating DVD from your Second Life session using mostly freeware and open source software.

Video Format

I won't go into deepest information about Video format, i suggest to read the excellent article of Chris Pirazzi Programmer's Guide to Video Systems. But take time to have a coffee before !!

In short for having a full quality video recording for a DVD PAL you will need to capture your video in 788x576 format (4:3 Square-Pixel) ; notice correct ratio should be 576x4/3 = 768; rescale it to 720x576 (4:3 Non-Square-Pixel) during the last MPEG2 coding of your DVD. However after all of this you will only see 702x576 pixels on your TV Screen. 788/768/720/702 : What for this hell ?

What size is a television picture ?

There are 576 active lines in a television picture (625 lines system). A 4:3 image would therefore be: 576 x 4/3 = 768 pixels wide.

However this assumes the pixels are square - but television pixels are not square (due, in part to the allocated bandwidth and Kell factors etc. ). They have an aspect ratio of approximately 1:1.094. A 4:3 television picture would therefore be: 768/1.094 = 702 non-square pixels wide

In the days of analogue television, the active part of a television line occupied approx 52 µs. When they came to digitize television, a sampling frequency of 13.5 MHz was the agreed compromise. If you multiply 52 µs x 13,5 MHz you get 702 samples per scan line. So a 4:3 television image is 702 pixels wide by 576 high.

The digital TV standard (originally known as REC 601) allocated 720 pixels per total line length. Digital pictures are effectively wider than analogue pictures by 18 pixels but the 4:3 image sits inside the 720 by 576 area. The additional 18 pixels are required for digital processing and it would be perfectly acceptable to leave them black - but if the image is shrunk via a digital DVE (Digital Video Effects), two 9 pixel wide black stripes will be seen at the sides.

These 18 pixels are of course not square, converting them to square pixels gives:
18 x 1.094 = 20 square pixels.

When making a 4:3 graphic on a square pixel device for conversion to a 720x576 (non square pixel) video image, the width of the 768x576 (square pixel) image must then be increased to:
768 + 20 = 788 square pixels.

Thus correct size of video capturing for a DVD PAL purpose is thus 788x576.

Windows Resizing

For having a precise capture of your Second Life session you will need to resize very precisely your Second Life viewer. Sizer tool of Brian Apps is the perfect tool to use.

If you size your Seconf Life Viewer to DVD PAL Capture Video Size 788x576, you will capture entire windows (Windows Frame, SL Menu and SL Toolbar). You may have situation you wanted to remove part of those elements from your capture (or not). You can also hide UI using Alt-F1 short keys of the viewer. To simplify everything custom arrangement of Windows UI have effect on Windows Frame Width & Height, Title Height of Non Client area.

Without any customization of Windows Default parameters, your SL Viewer will use the following dimensions:
  • Windows Frame Width 4 px

  • Windows Frame Height 4 px

  • Windows Title Height 30 px

  • SL Menu Height (18 px) + Shadow (5px) 23px

  • SL Toolbar Height 29 px

  • SL Audio Video Toolbar Height 24 px

Depending of your Video Capture needs (and for having a perfect capture windows of 788x576) you will have to resize your SL Viewer Windows with dimensions (Height & Width) specified bellow:

1 - Capturing All Interface 788x576

2 - Capturing SL Viewer MTAV (Menu + Toolbar + Audio Video Toolbar) without Windows UI 796x610. This scenario can be also used to capture 3D only when using [Ctrl] [Alt] [F1] Shortcut (Hide SL User Interface).

3 - Capturing SL Viewer TAV (Toolbar + Audio Video) without Windows UI 796x633

4 - Capturing SL Viewer AV (Audio Video) without Windows UI 796x662

5 - Capturing SL Viewer 3D without Windows UI 796x686

Windows Width788796796796796
Windows Height576610633662686
X1 Offset04444
X2 Offset04444
Y1 Offset035535353
Y2 Offset0443357

* Or 3D with Ctrl-Alt F1 shorcut

We will use later the Offset values into parameters of capturing video software.

End of Video Tutorial Part 1 - Next part to come How to capture with Virtual DUB
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