Digital Video Media

David Owens Software Engineering Department University of Wisconsin Platteville [email protected]

Abstract

As capabilities of computers increases, so increases their usefulness in manipulation and distribution of digital video information. Many different software systems have been created to edit and distribute video media files. These software packages have different strengths and weaknesses when compared together. The use of such software systems to distribute digital media causes numerous legal and ethical concerns. Software systems designed to control such distribution can also cause ethical concerns. Digital media in general will be addressed; however, video media will be emphasized.

Introduction

There is some important information a person should know before attempting to edit digital media. Foremost, they should know the basics of how a video file works and how different editors manipulate them. Beyond that, they should be familiar with encoding and the types of codecs. Lastly, it is important to know the ethical limitations placed on editing video.

Video Basics

Digital video is composed of typically two or more major parts, called streams. The two most common streams are the video and audio stream. There can also be additional streams for subtitles or other information, but they aren’t as common and won’t be covered.

Streams

Streams can be thought of as separate synchronized play-lists or queues that are played or iterated through. By this, I mean that when a player begins playing a file, it starts playing all streams at the same time. These streams stay synchronized so that voices match mouth movements, music plays on cue, and the correct sounds play at the correct times. Streams are a way to abstract the multiple elements of a digital video that execute over the duration of the video.

Audio

The audio stream is unnecessary for a video file, but is common. This stream supplies the sound, voice and music associated with the video. Most digital videos contain an audio stream.

Video

This stream is required for a digital video. This contains the video or frame data needed to display the video content to the screen. The way this data is stored may vary.

Video Encoding

In its native format, even short clips of digital video can fill several gigabytes of data storage. Even with larger hard disks in modern computers, this is still a large amount of storage required. Files of this size would be difficult to send over any sort of data connection. Because of these constraints, video files are virtually always compressed by some method. The process by which a video is compressed is called encoding. The process by which a compressed video is read and the compression deciphered is called decoding. The software used to encode and decode video are called codecs. The word “codec” is a combination of the words ‘encode” and “decode”.

Lossless Codec

A lossless codec is a codec which encodes data in such a way that the original video data can be perfectly restored. Think of it as merely compressing each frame into a “*.zip” file. These sorts of codecs are useful when high standards of video quality are required. This higher quality usually comes at the expense of file sizes.

HuffYUV

HuffYUV is a popular lossless codec. In addition to being lossless, the codec is optimized for speed. This allows files to be encoded and decoded rather quickly. This added speed can be useful given that the file size can be rather large. The file-size of HuffYUV files is not nearly the size of uncompressed video, but a good estimator is to allow 100 megabytes for every ten seconds of video. The dimensions of the video can also affect the filesize. [3]

Lossey Codec

A lossey codec typically reduces the video’s file size dramatically but some video information is lost. The amount of information lost compared to the resulting file size can usually be configured. The difference in quality and file size can vary greatly based on the codec and settings. A 3-5 minute video file can retain a reasonably good amount of quality and still be within 50 to 100 megabytes with some codecs and settings.

Divx

Divx is a common codec. It is readily available online and is fairly well known. This codec yields good compression which makes it a good choice for compressing videos to be downloaded over the internet. One of the major ways in which it lowers file size is by key-framing. A key-frame in a video file is a frame that other frames will be based on. The key-frame is typically the first frame after a scene change or charge in the “shot”. The key-frame is stored very close to the original frame while only the changes to this frame are stored to construct the frames until the next key-frame. As a proprietary codec, a license is required if used for profit. [1]

Xvid

I’ve found Xvid to be very similar to Divx in practice. In fact, Xvid derives its name by simply reversing the letters in Divx. It yields very similar compression ratios and similarly uses a key-framing system. Xvid also has the claim of being mpeg 4 ISO compliant. This ensures that any system capable of decoding that standardized format can decode Xvid files. I found no such claim made by Divx, but this doesn’t mean it is not compliant. Xvid is also an open-source project, making it free for all uses. [2]

Video Editing

Video editing is the process by which one changes and manipulates video data. This can include combining clips together in a sequence, adding special effects, or overlaying text or a logo.

Timelines In most digital video editing programs, the video stream is represented as a timeline. To help illustrate the concept of a timeline, imagine a strip of film for a normal movie projector. Keep the image of strips of film in your mind as you read the following examples.

Single Timeline

Imagine that you want to simply cut the film and rearrange the clips. To do this, you would simply cut the film and arrange them as necessary. Afterward, you are left again with one single strip of film progressing from left to right. A single series of clips is, in essence, a timeline.

Multiple timeline

For this example, imagine that instead of having a single strip of film, that you have several. Suppose you ant to do more than simply re-arrange clips. You might want to layer one clip which has some transparent regions on top of another clip. Perhaps you want to slowly fade from one clip into another. Each individual timeline is similar to the single timeline example. However, with multiple timeline systems, timelines can be layered on top of each other for various effects.

Codec Support

Different video editing packages have different levels of support for different codecs. Some systems will only support specific codecs while other systems will disallow specific codecs.

Ease of Use and User Interface

The ease of use of a video editor’s user interface leaves much to personal opinion. However, simple observations can still be made. The system may sacrifice versatility for simplicity or vice versa.

Review of Editing Programs

Different editing packages have different strengths and weaknesses. It isn’t uncommon for any number of different editors to be used for different sections of the same project to take advantage of these different strengths. Following are brief observations of several editing packages. Windows Movie Maker

This program is one of the most common editing packages. This is simply because it comes packaged with Windows XP. However, it shouldn’t be immediately overlooked. Its major strength is its very generous learning curve and ease of use. It’s very easy for beginners but it lacks many of the features an experienced video editor might want. It has good codec support for importing files into a project, but it limits the files it exports to the Microsoft owned Windows Media Video format. Files that are imported can be immediately broken into clips. These clips can then be arranged in a sequence on the single available video timeline. There is also the capability for some simple audio adjustment.

Figure 1: Windows Movie Maker

VirtualDub

VirtualDub is a fairly small, yet powerful video editing tool. It supports nearly any codec that is installed on the given computer except for the asf and wmv formats. Those are Microsoft proprietary formats and Microsoft had threatened legal action if VirtualDub continued support for those formats. VirtualDub has a reasonably simple interface that is obvious to most users. It only handles one video timeline, which limits it’s capabilities for higher editing functions. However, its primary strength is its many exporting options and the simple filters it can apply. It also is efficient with resources. It’s very easy to have multiple instances of this program open, working on separate files, at the same time. Also, because of its size, it loads very fast compared to more versatile programs that have more to load. This program is ideal for smaller editing tasks such as resizing a video or clipping off edges. On a personal note, I’ve found this program very useful for handling small tasks. Additionally, it’s very tolerant of corrupted video files. [4]

Figure 2: VirtualDub

Adobe Premiere

Adobe Premiere is a good example of a fully-featured video editing package. It allows for multiple visible timelines which allow the user to create complex image compositions and scene transitions. It allows for many audio timelines as well which allows for the editor to add several music tracks along with sound effects and voice tracks. There are also many built-in tools for manipulating individual video and audio tracks. It supports many codecs and allows for many choices of codecs for exporting. Despite being more complex than other editors, it remains fairly intuitive. The user can see the video and audio tracks on the timeline as well as preview their work. These features aren’t free however. Being a complete professional package, Premiere typically has a price tag between $100 and $300.

Figure 3: Adobe Premiere

Jahshaka

There’s very little that I can say about Jahshaka. I was originally interested in it because it was open-source. I thought it might be a viable alternative to Adobe Premiere. However, on the several occasions in which I have attempted to use it, I have never been able to successfully create a project. As it stands, it is an example of a poor user interface. The controls are ambiguous and it gives very little output as to what the program is doing. Additionally, there’s very little built in assistance for beginners. In its defense, some have been able to successfully use this program to create visual special effects. Figure 4: Jahshaka

Video Media Ethics

The programs reviewed here make editing digital media very simple. The large amount of available codecs allows people to compress video files down to sizes that are easily transferable over the internet. The ease of distributing and editing digital media causes some issues in regards to copyright. Companies go to lengths to stop users from copying and distributing their copyrighted works. At the same time, benevolent users try to preserve their rights in regards to media they rightfully obtained. Both campaigns can foster ethical issues regarding copyrights.

Companies Protecting Copyrights

Copyright holding companies have made several attempts to protect their rights. However, these attempts can sometimes be questionable.

Sony DRM At one point, Sony implemented a Data Rights Management system which would install software onto a user’s computer to disallow them from copying their music CDs. However, these systems would potentially install without the user’s consent. One such way was by using the “autorun” feature of Windows. Performing actions on the user’s computer without consent can very easily be seen as unethical. Additionally, the software installed could corrupt system files and create security holes. Once the effects of such systems were found, Sony had to respond to legal ramifications. [6]

Individuals Violating Copyrights

It’s very easy to distribute copyrighted materials illegally over the internet. However, lawful users of copyrighted materials have certain rights regarding these same materials. These rights fall under the category of fair use. Fair use, section 107 of copyright law, allows for users to reproduce copyrighted materials for several reasons. These reasons include criticism, comment, news reporting, teaching, scholarship, and research. To help determine what constitutes fair use, the following issues are considered: the character of the use, the nature of the original copyrighted work, the amount of the work used, and the effect on the potential market. The way that the original author presented the information is what is copyrighted. The information itself can be reproduced freely. [5]

References

[1] Divx, Retrieved February 2006 www.divx.com

[2] Xvid, Retrieved February 2006 http://www.xvid.org/

[3] HuffYUV v2.1.1, Retrieved February 2006 http://neuron2.net/www.math.berkeley.edu/benrg/huffyuv.html

[4] VirtualDub.org, Retrieved February 2006 www.virtualdub.org

[6] Lessons from the Sony CD DRM Episode, J. Alex Halderman and Edward W. Felten, Center for Information Technology Policy, Department of Computer Science, Princeton University