Discuss Project Report

Very helpful notes on video codecs. I'm not looking for details on the whole notes. However it will explain things that you don't understand about MPEG.

DVI - Digital Video Interface

CCD imager

Video tips

Computer monitors typically (unless low quality) do not interlace an image. TV displays odd and even lines of a frame. This was do to the fact the when early TVs drew the full frame at once, it would begin to fade from the phosphors on the screen. With even & odd scan lines, the fading wouldn't be as noticeable. These 2 sets are called fields. Odd & Even fields. Interlacing blends the two fields together. Since computer monitors are none interlaced, if you want your videos rendered on the computer for display on TV you need to do field rendering to digitally create interlacing of fields. Frame rate of 30 fps (actually 29.97 fps) is with 2 interlaced fields per frame. This gives a field rate of 60 (59.94) fields per second.

Most computers can't handle displaying full screen uncompressed video at 30 frames per second. A single frame of a 640 x 480 @ 24 bits in color depth takes up nearly 1 MB. At 30 fps, that's nearly 30 MB for 1 second of video. A 32x CD ROM, can only read 4.8 MB per second.

To see movie you must see rapid moving images on screen. This gives the illusion of moving objects. 30 fps (frames per second) is typical motion video (29.97 fps on the PC). However 15 fps is also adequate.

For uncompressed video, in 1 second of animation the formula for file
size is:

frames/second x image size x color depth (in bytes) = file size

So running 30 fps at (640 x 480) and 256 colors (8 bits = 1 byte)

30 x 307200 x 1 = 9,216,000 bytes or 9.216 MB for 1 second of animation

As you can see, video compression is greatly needed. A way of reducing the image file size is reducing the video size, color depth, and frame rate. 15 fps, at 320 x 240, at 256 colors is adequate.

Compression:

There are 2 types of compression.

CODECs are used to enCODe / DECode a file. Without the same CODEC installed users can't play the files you compress.

Wavelet Compression - Representing an image as a set of mathematical expressions

Lossy is good for video, since some small drops in moving images are not noticeable.

H.264 Link

Links of interest:
Quicktime
AVI
MPEG 1, 2, 4

Video formats: QuickTime (MOV) for the Mac, Audio Video Interleaved (AVI) for Windows.
Interleaving mean to blend audio data with video data and other data so that the sound remains synchronized with the video.

QuickTime format can have various tracks of data. Such as multiple language tracks. Sorensen codec is very good.

You can get a QuickTime production package to create videos in the QuickTime format (or convert from QuickTime to another format).

AVIs & MOVs don't require any special hardware to playpack the files.

Compression ratios
Most computers can't handle displaying full screen uncompressed video at 30 frames per second. A single frame of a 640 x 480 @ 24 bits in color depth takes up nearly 1 MB. At 30 fps, that's nearly 30 MB for 1 second of video. A 32x CD ROM, can only read 4.8 MB per second.Integrated software applications or drivers, called Codecs take care of this dilemma for you. These drivers compress the video file into a smaller file and little compromise to the quality of the image.There are 2 types of compression

Different codecs will work the compression in two kinds of ways

Deltas in a video

MPEGs: Keyframes & Macroblocks

DVDs (Digital Versatilbe Discs) are a hardware format that defines the physical process in which data is written to the disc. The software or digital information on the disc contain multiplexed audio, video, text, and other data for display on the screen. MPEG-2 uses a JPEG method for storing each keyframe. Frames in-between the keyframes are the difference from frame to frame. This process of the difference between frames is called delta-frame encoding.

"MPEG-2 can represent interlaced or progressive video sequences, whereas MPEG-1 is strictly meant for progressive sequences since the target application was Compact Disc video coded at 1.2 Mbit/sec." MPEG2-FAQ

MPEG-4 - "Wavelet-based MPEG-4 files are smaller than JPEG or QuickTime files, so they are designed to transmit video and images over a narrower bandwidth and can mix video with text, graphics and 2-D and 3-D animation layers." Gotten from here

Movie editors - Adobe Premiere & After Effects. Rearrange clips, do special effects, titles, etc.

Mophing of images

Digital TV - How Digital TV Works. A camera rasterizes the scene by turning the image into a series of pixels. Horizontal & Vertical sync signals define the ends of lines or frames. Digital TV will be pure digital all the way to the display. Unlike Digital Satellite TV where it's converted to analog for display.

HDTV - High definition television. This will replace NTSC as the video standard for the US. "An NTSC TV image has 525 horizontal lines per frame (complete screen image). These lines are scanned from left to right, and from top to bottom. Every other line is skipped. Thus it takes two screen scans to complete a frame: one scan for the odd-numbered horizontal lines, and another scan for the even-numbered lines. Each half-frame screen scan takes approximately 1/60 of a second; a complete frame is scanned every 1/30 second. This alternate-line scanning system is known as interlacing. Like SECAM, PAL scans the cathode ray tube (CRT) horizontally 625 times to form the video image. NTSC scans 525 lines. Color definitions between the systems vary slightly." PAL & SECAM are non-US standards"

HDTV will use

Standard TV uses a screen ratio of 4:3. HDTV can us 16:9 ratio for wide screen shows.

SDTV - Standard Definition Television.

"Standard definition television (SDTV) is a digital television (DTV) format that provides a picture quality similar to digital versatile disk (DVD). SDTV and high definition television (HDTV) are the two categories of display formats for digital television (DTV) transmissions, which are becoming the standard. HDTV provides a higher quality display, with a vertical resolution display from 720p to 1080i (p is progressive, i is interlaced) and higher and an aspect ratio (the width to height ratio of the screen) of 16:9, for a viewing experience similar to watching a movie. In comparison, SDTV has a range of lower resolutions and no defined aspect ratio. New television sets will be either HDTV-capable or SDTV-capable, with receivers that can convert the signal to their native display format. SDTV, in common with HDTV, uses the MPEG-2 file compression method.

Because a compressed SDTV digital signal is smaller than a compressed HDTV signal, broadcasters can transmit up to five SDTV programs simultaneously instead of just one HDTV program. This is multicasting. Multicasting is an attractive feature because television stations can receive additional revenue from the additional advertising these extra programs provide. With today's analog television system, only one program at a time can be transmitted."

Vertical-Blank Interval - This is the gap in-between the frames on a TV picture. Closed captioning makes use of this. However you can send more than just text, you can send data. Intel invented Intercast to transmit web pages and other information behind the scenes of a TV show. WebTV allows you to have interactive TV shows where you can play games or get facts about what you are watching.

Get Windows Media Encoder to do screen captures with voiceovers.

Printscreen in windows:

To capture the contents of a window, click on it so it's active and then press ALT+PRINT SCREEN.

To capture the contents of the screen, press PRINT SCREEN.

Now go to Paint or any other image program and paste the image to print it out. Paint is found in Start/Programs/Accessories/Paint.