Video -- basic technical information

by Migdio Dominguez and Ursula Hoffmann


File sizes:

Uncompressed 24-bit Still Graphic
640 x 480 pixels = 307,200 pixels per frame
307,200 x 24 bits per pixel /8 (bits per byte) = 921,600 bytes per frame <>The amount of bit-depth reduction is greater for graphics with few colors such as line drawings or illustrations. Photographic images require many colors so compression usually gives better results.  JPEG and GIF formats work well.  Select the compression rate you want. 20-75 % compression and resizing of digital photos for use on a computer produces an acceptable compromise between quality and file size.  Test. 

Uncompressed 24-bit Video
("legal" video is 29.97 frames per second and thus smaller; YUV color space is 16-bit so files are smaller)

640 x 480 pixels = 307,200 pixels per frame -- TV quality
307,200 x 24 bits x byte/8 bits = 921,600 bytes per frame
921,600 x 30 frames per second = 27.648 MB -- 30 fps is desirable.

Reducing the frame size to 320x240 (one quarter size) is preferred for computer monitor display.
Reducing the frame rate to 24 fps is acceptable.

Reducing the frame rate to 10 fps may produce choppy quality and leaves the data rate at 2.3 MByte/sec. (This data rate is too high for old hard drives, old CD-ROM (2x drive ~ 200 Kbyte/sec sustained ) or modems (28.8 modem ~2.88 Kbyte/sec; 56.6 modem~5.66 Kbyte/sec).

Greater compression will knock this down further, but higher bit-depths make compressed video look better.

Codecs (compressor/decompressor):
Cinepak, Indeo and Power Video are the best codec choices for CD-ROM playback with QuickTime or Video For Windows. These codecs don't currently support streaming or yield good picture quality at the low data rates required for Web delivery. Solutions for this class of video include Real Media, VDOLive, Xing, TrueStream,Vivo, Vosaic and VXtreme.

Current compressed formats:
For more information, see
What is a codec?  http://www.webopedia.com/TERM/c/codec.html
List of codecs  http://www.siggraph.org/education/materials/HyperGraph/video/codecs/Default.htm
determine the correct codec  http://www.leadtools.com/utilities/video-codecs/codec_converter.htm

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Credits for the above material:
File sizes: San Francisco State University: http://msp.sfsu.edu/Instructors/rey/video/bandwidth/filesize.html  -- some of these data are somewhat dated.
Migdio Dominguez at Lehman/CUNY -- May 2005

Hardware needed to produce NTSC video clips:

One second of captured video will need about 15 megabytes of disk space.
One minute of captured video (high quality DV/AVI format) will need 178 Mb of disk space. So, 3 minutes will fill a CD ROM.
One hour of captured video will take up about 13 gigabytes on your hard disk.

You therefore need a hard disk with a lot of free space, preferably contiguous (use defrag before capturing a movie) -- better yet, use a second hard disk dedicated to audio/video work only, so you can completely erase it between projects.

You need a video capture card to capture video from a VCR.
You need a digital video camera / mini DV cam.  (Mini-DV is much better than VHS.)  Professional models ($5000-$6000) have 16:9 widescreen and 4:3 aspect ratio shooting formats, 30 or 24 frame rates, and 3CCD to process RGB separately. Simpler models ($600 and up) have a single CCD chip for RGB primary color filtering.

To capture video from a mini DV cam (IEEE 1394, with firewire cable--4 pin and 6 pin), you need

1) a video capture card and FireWire (IEEE 1394) to connect the camera to the PC; now the PC controls the camera --Mac has this built-in)
2) a PCI adapter card or built-in FireWire to hook up a DV camcorder
or
3) a USB port or External Video Adapter -- plug in an analog video cable from the camcorder or VCR
and
4) an external hard drive (128 GB)
5) a fast processor (1.5 GB and up).
A USB2 hard drive has faster throughput than FireWire:
The USB2 port has a data rate of 480 Mb/s (60 MB/sec), or slightly faster than FireWire. With the faster rate, new external disk drives and even video cameras are starting to include USB2 interfaces, often in addition to a FireWire interface.

For creating a CD or DVD, you need a CD or DVD burner - drive.
Currently, the maximum speed of a CD burner is 32 X--you need a CD burner 12 X minimum; that of a DVD burner is 8 X.  When you buy media, make sure that their speed agrees with that of the burner, or lower its settings so that it will create the CD or DVD at the speed the disk is designed for.

References:
Video capture hardware (June 1999--may be too dated):  http://www.manifest-tech.com/media_pc/pc_video_hw.htm
USB2 Video capture hardware (April 2003):  http://www.manifest-tech.com/media_pc/usb2_video.htm
USB2 specs (2004):  http://usa.aopen.com/tech/techinside/usb2.htm

Software needed:

Windows XP comes with Windows Movie Maker 2 (in the folder Accessories) which allows you to capture video from a camcorder or VCR. Then you can make basic edits with NLE (non-linear editing), cutting and pasting, inserting transitions and effects, and adding titles and credits. Finally, you can save in DV/AVI format (highest quality for a  DVD -- 30 seconds = 116 Mb), or in compressed WMV format for e-mail or a web page or CD (30 seconds = 2 Mb).

The Mac's imovie is the equivalent. It has a very neat interface and it lets you save in Quicktime .qt or .avi format or create a DVD.

(For professional work, you need to buy better video editing software.)

Attach the camera to your PC with FireWire and open Windows Movie Maker.
To capture film from the camera, set the control to Play VCR -- that way the PC controls the camera and you can easily adjust settings shown on the PC, start and stop.
If the control is not set to Play VCR, you can record live directly to the computer.

Always record at highest quality, Export/Save in any format that your target audience can use. For a long video, create CD or DVD disks.

After editing your video, save it in a format that can be used by your audience:
Large files must go on a web server that can handle streaming video, or on a CD or DVD.
Very small files, compressed, can be uploaded to your website or to Blackboard, for viewing online or for downloading to someone else's computer.

Make sure that they work with one of the three or four currently most popular players/viewers all of which are free downloads and easy to install:

QuickTime, Real, Windows Media Player, Winamp.  The latest version of QuickTime Pro (v. 7) is excellent.

References:
Windows Movie Maker 2 (included in Windows XP -- make sure you have downloaded the latest service pack):

review and how-to tips  http://www.winsupersite.com/reviews/wmm2.asp
tutorial:  http://www.windowsmoviemakers.net/
articles: http://www.windowsmoviemakers.net/Articles/Index.aspx
tutorials and articles: http://www.windowsmoviemakers.net/Tutorials/Index.aspx

Digitizing audio and video (Feb. 2002):  http://www.cit.cornell.edu/atc/materials/dig/videoformats.shtml

PCWorld Digital Video Camera buying guide (April 2005):  http://www.pcworld.idg.com.au/index.php/id;1847886895;pp;1;taxid;56789

last revised May 2005