Monday, March 28, 2005

DivX Online Video Streaming

DivX® is a video codec created at DivXNetworks Inc., known for its ability to compress lengthy video segments into small sizes and has been the center of controversy because of its use in the replication and distribution of copyrighted DVDs. Many newer DVD players are able to play DivX movies.

DivX is not to be confused with DIVX, an unrelated attempt at a new DVD rental system employed by the US retailer Circuit City. Early versions of the DivX codec were named "DivX ;-)", where the winking emoticon was a tongue-in-cheek reference to the failed DIVX system.

A typical feature-length movie on DVD is around 7 gigabytes in size; with DivX this can be compressed to around 700 megabytes which fits on a CD-ROM with minimal loss in quality. Various programs are available which can produce a DivX file from a normal video DVD (this process is known as "ripping"). The resulting file can then be stored on hard disk, burned on optical media, or be shared on peer-to-peer networks.

DivX ;-) 3.11 Alpha and earlier versions generally refer to a hacked version of the Microsoft MPEG-4 Part 2 video codec, extracted around 1999 by French hacker Jerome Rota (also known as Gej). The Microsoft codec, originally created for the compression of *.asf files, was altered to allow compression to *.avi files. From 1998 through 2002, independent enthusiasts within the DVD-ripping community created software tools that dramatically enhanced the quality of video files that the DivX ;-) 3.11 Alpha codec can produce. One notable tool is Nandub, a modification of the open-source VirtualDub, which features two-pass encoding (termed "Smart Bitrate Control" or SBC) as well as access to internal codec features.

Rota's company DivXNetworks, Inc. eventually produced a clean room version of the codec, thus avoiding potential copyright problems with Microsoft. This codec was named DivX 4, dropping the smiley. DivXNetworks has applied for a patent for their new codec, which is fully MPEG-4-Advanced Simple Profile compliant.

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Friday, March 25, 2005

How MPEG Works

The MPEG codecs use lossy data compression using transform codecs. In lossy transform codecs, samples of picture or sound are taken, chopped into small segments, transformed into a frequency space, and quantized. The resulting quantized values are then entropy coded.
The moving picture coding systems such as MPEG-1, MPEG-2, and MPEG-4 add an extra step, where the picture content is predicted from past reconstructed images before coding, and only the differences from the reconstructed pictures, and any extra information needed to perform the prediction, are coded.
MPEG standardizes only the bitstream format and the decoder. The encoder is not standardized in any way but there are reference implementations available for members that produce valid bitstreams. That means that any MPEG-4 decoder can decode any MPEG-4 material (of the same type) regardless of the encoder which produced that material.

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Thursday, March 17, 2005

High Definition Video

High Definition Video (HDV) is a video format which is intended to provide the facility to record high-definition (as opposed to standard definition) MPEG-2 video on standard DV media (DV or MiniDV cassette tape).
The HDV format was defined by four companies: Canon Inc., Sharp Corporation, Sony Corporation, and Victor Company of Japan, Limited (JVC). These companies originally announced their HDV partnership in September, 2003. They have been joined by other companies such as Apple Computer.
In January 2005, Apple announced versions of iMovie and Final Cut Express that can import and edit HDV. Because HDV is a consumer version of high definition it is not supported by their high-end product, Final Cut Pro, without a plug-in called Lumière HD, Lumière contains full support for HDV for Final Cut Pro.
Some other popular video editing software packages, like Adobe Premiere Pro, now include limited support for editing HDV.

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Sunday, March 13, 2005

Equipment for Video Editing

Non-linear editing for film and television postproduction is a popular modern editing method. Video and sound are digitised to hard disks. After that, they can be manipulated with software such as Pinnacle Liquid, Avid, Final Cut Pro or Lightworks.
Compared to the linear method of tape-to-tape editing, non-linear editing offers the flexibility of film editing with random access and easy project organization. It is easy to make new versions nondestructively. Initially, only low-resolution pictures could be digitized, as storage was limited and expensive. Broadcast quality and High definition are now possible. The costs of the editing systems have dropped, bringing non-linear editing within reach of a domestic user with a good home computer.
The earliest non-linear film and video editors used laserdisc storage, but were quickly superseded by editing systems that used computer disk storage and compressed video.
The elements of a computer-based non-linear editing system for video are a computer with a video editing card or video capture card and video editing software. Digital video is imported into the computer through a firewire socket and analogue video is imported through composite sockets both of which are found on most video editing cards. Various editing tasks can then be performed on the imported video before it is saved, exported to another medium, or MPEG encoded for transfer to a DVD.

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Thursday, March 10, 2005

Film Ratings

The stated purpose of rating films is to allow parents to make informed decisions on their childrens' entertainment. Film rating systems assign classifications to films based on their content. The guidelines laid out by rating systems is often used by governments and theatre trade groups to restrict the viewing of certain films to patrons above a certain age. There are a number of film rating systems worldwide:
Australia rates films through the Classification Board of the Office of Film and Literature Classification (Australia).
Canada has seven different rating systems for its many provinces and territories, with the Canadian Motion Picture Distributors Association offering yet another one.
New Zealand uses a system devised by the Office of Film and Literature Classification (New Zealand).
The United Kingdom uses a system devised by the British Board of Film Classification.
The United States uses the MPAA film rating system, instituted by the Motion Picture Association of America.
Germany has the FSK (http://www.fsk.de) (Freiwillige Selbstkontrolle der Filmwirtschaft; voluntary self-control of the Motion Picture Association) rating system based on the age of the audience. Steps are as follows:
no restriction, all age groups
only for persons of 6 years and older
only for persons of 12 years and older
only for persons of 16 years and older
adults only (an adult in Germany is 18 years and older)

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