Applications for MPEG Playback Control

Background - What is MPEG?

MPEG stands for "Motion Picture Experts Group", a consortium of participants charged with developing standards for the encoding, storage, transmission, and playback of compressed digital video.

The earliest standard developed, now called MPEG1, was designed to pack a full 74 minutes of video onto a compact disc (CD). These CDs were marketed as Video CDs. Although a great technical achievement to pack that much video into such a limited amount of data storage, the resulting quality issues compared to video tape prevented the format from achieving widespread commercial success, at least in the USA.

A side-effect of MPEG1 was its audio compression technology. The portion of MPEG1 dedicated to audio was called “MPEG Layer 3”, and proved popular purely as an audio format. Today’s widespread adoption of on-line music is via this format, now abbreviated MP3.

MPEG2 was developed as a more versatile, adaptable standard which could support high video quality where adequate bandwidth or storage capacity were available. Variants of MPEG2 are now used in satellite TV broadcasting (Dish Network) and in the popular DVD format.

Advantages of Digital Video

The primary advantage of digital video is repeatability without degradation. Playing back a conventional video tape multiple times gradually introduces wear. After dozens of repeated viewings, no matter how high the original quality, the tape will develop artifacts such as dropouts, sync errors, etc.

For most all digital storage methods, no physical contact occurs when accessed. The read/write head of a hard drive floats on a cushion of air just microns above the rotating disc. The information on a CD or DVD is read by a laser which does not touch the disc. Thus, multiple playbacks are possible without degradation of quality. Furthermore, exact data backups can be created, to guard against media loss or damage, which are identical to the original.

Digital format standards such as MPEG also feature redundant data and error detection code which allows, for example, a DVD player to compensate for data lost due to a scratch or a bump in the road. A satellite receiver can compensate for a few lost frames due to a bird flying past the dish or transmission loss caused by solar activity.

Another important feature of digital video, being data by nature, is transportability. Digital video can go anywhere data can go – even via the Internet. Instead of needing to transport tapes physically to a transmission facility or playback site, the video files can be uploaded to a remote player for later viewing, while still maintaining the exact quality of the original.

The Aavelin Display Rendering Method

The MagicBox Aavelin display system operates using a “real-time” display algorithm. In this context, real-time means that the display is completely redrawn in synchronization with each scan of the electron beam down the face of a monitor. Every “frame” of the video signal is completely new.

In a system that normally displays still slides and advertisements, the advantages of this method may not be immediately apparent. But a digital signage display system is seldom truly “still”. While one page is being displayed, others are being prepared. Messages are generally crawling superimposed at the top or bottom of the screen. Weather data is being updated continuously and displayed, while the time and date are often shown with the seconds ticking away.

By developing a system that is prioritized around completely redrawing all of the information it needs to display at a rate of approximately 60 times per second ensures a software architecture that is free from deadlocks, display artifacts, and from a viewers’ perspective, “glitches” and “hiccups.” The practical end result is crawl lines that operate completely smoothly, and transitions between slides that are perceived as gliding, rather than forceful.

In relation to the display of video streams, this display architecture is just as capable of drawing completely new and changing data onto the screen every frame as it is of reproducing still frames. This makes the Aavelin well suited to acquiring, formatting, and displaying live video (in conjunction with the necessary acquisition hardware) concurrently with other processes such as crawl lines, whereas systems based on traditional operating-system supplied video streams can be at the mercy of that system, presenting display pauses and errors as a system that is not designed for real-time response attempts to keep up with every frame of video.

External Signal Acquisition and Display

An incoming video signal, such as from an MPEG playback device or a live camera feed, is input into the Aavelin using an optional video capture card.

This card takes the video information present at its external connectors and converts it into a signal which is fed directly into the video display controller chipset of the Aavelin. This is the same video controller chipset which the Aavelin refreshes with every frame to display its regular information.

The Aavelin, by setting special bits on-the-fly, can specify whether any given pixel (a pixel is the smallest independently changeable element of a video picture) represents the internal display or the input signal. Using this method, Aavelin display elements such as crawl lines, the time and date, and still pages which are transitioning in or out of the display, can be combined with a moving video signal.

Additionally, the video capture card contains repositioning and scaling logic, which can resample the input signal on-the-fly into a given rectangle. By synchronizing with this hardware process and selectively displaying only the video pixels input into this rectangle, the Aavelin can achieve the effect known as “Video in a Window” or “Picture in Picture”, allowing a scaled image of the video signal to operate in any region of the final display while other elements proceed regularly.

This video acquisition and display process is different from a similar process known as “downstream keying”, although it is often referred to by similar terms. In true analog keying, the input signal is not manipulated by the PC device and is not present within the video display circuitry.

The real-time process employed by the Aavelin has the desirable artifact of up-converting the incoming signal to VGA, meaning that the signal from a video feed, while still being re-output as video by the Aavelin, can also be displayed on other devices such as VGA and LCD monitors and plasma screens.

The Missing Link – Integrated Device Control

The ability to combine video feeds with digital signage in hardware is only as practical in the real world as the software that manages the process.

The Aavelin playback software and the Aavelin Composer software contain built-in functions to control MPEG playback devices, such as the Adtec Soloist and Adtec Edje series.

These related Adtec products allow users to store and upload libraries of MPEG video clips and organize them by name. Likewise, the Aavelin software contains fields for every “page” in a project where the name of a corresponding video clip can be entered. This allows for seamless scheduling and control of when clips (or entire programs) play back, and what Aavelin pages and features are displayed simultaneously, rather than having to rely on two separate device schedules synchronized by two different clocks.

Additionally, the Aavelin features a “timer events” scheduling method which is unlinked to pages, and allows external video events on the Adtec players to be triggered at specific times, such as the playback of scheduled long-form community programming at regular times.

Applications

By combining the Aavelin’s display abilities with the video storage and playback abilities of external devices such as the Adtec products, or with live camera feeds, a number of potential market applications can be configured:

• A photo-classified channel can display short commercial clips between still advertisements for cars or homes.
• An in-store retail display system can alternate still slides of local and daily specials and events with store-chain and brand supplied video advertisements.
• A hospitality channel can integrate hotel event and conference schedules with advertisements for restaurants and services, or show a live camera feed of the local weather or the pool.
• A community access or government channel can maintain a repository of locally-produced full-length programs, displayed according to a regular schedule, and display slide-based community announcements at other times.

In all of the above applications, features can be mixed and matched, such as maintaining a crawl line on top of full-length programs to convey important information, or maintaining a corner logo (“logo bug”) and the time and date.

Conclusion

The list of potential applications for an integrated, real-time digital signage and MPEG playback environment continues to grow. The Aavelin’s unique architecture compliments the ever changing requirements of the digital signage customer base.

With the increasing availability of broadband internet and PC-based digital video editing and encoding software, and the advent of low-cost, networkable playback devices such as those from Adtec, the variety of tasks which may be accomplished at low cost using MPEG technology are sure to increase in turn.

About MagicBox

MagicBox, Inc. has been manufacturing Character Generators and Video Messaging Systems, for CATV, CCTV, Satellite and Digital Signage applications since 1992. Customers have expanded from cable to include education, government, hospitality, medical, and corporate applications. Product development is focused on ease of use and integration with other systems. For more information, visit www.magicboxinc.com.

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