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Multimedia Operating System
You can say multimedia are digital movies, videos, clips, music, etc. The term "multimedia" refers to more than one medium or a combination of different mediums.
Using your personal computer to present information and entertainment in the form of music, digital movies, and video clips are all common practices in today's society.
You can store your desired audio and video files and play them later on demand. The disc has the capacity to store both audio and video files.
The characteristics of traditional text files, which the current file system was designed for, are very different from those of audio and video files, which are very different from each other. Because of this, a new kind of file system must be required solely for the purpose of managing audio and video files.
Keeping the audio and video files in storage and being able to play them back on demand places new demands not only on the scheduler but also on other components of the operating system. Because of this, it is necessary to design an operating system that is also capable of playing multimedia files; the operating systems that are capable of doing so are also known as multimedia operating systems.
At this point in time, almost every type of operating system can be classified as a multimedia operating system. This article on multimedia operating systems is divided into the following sections:
- Multimedia Files
- Audio Encoding
- Video Encoding
- Video Compression
- Multimedia Process Scheduling
- Multimedia File System Paradigms
- File Placement
- Caching
- Disk Scheduling
Multimedia Files
An ordinary text file in most computer systems consists of a linear sequence of bytes with no structure that the operating system is aware of or cares about. With the addition of multimedia files, the situation becomes more complicated.
To begin with, audio and video are completely different types of multimedia files. They are captured by different devices (CCD chip vs. microphone), have different internal structures (audio has 44100 samples per second vs. video's 25-30 frames per second), and are played back by different devices (monitor versus loudspeakers).
Audio Encoding
A sound wave, also known as an audio wave, is essentially the same thing as a 1-D (one-dimensional) pressure wave or an acoustic wave.
An acoustic wave that enters the ear causes the eardrum to vibrate, which in turn causes the tiny bores in the inner ear to vibrate along with it. This causes nerve pulses to be sent to the brain. The listener hears these pulses that never stop occurring in their minds as sounds.
In a similar manner, whenever an acoustic wave strikes a microphone, the microphone generates an electrical signal that represents the sound amplitude as a function of time. This signal is then sent to the processing unit where it is analyzed.
The frequency range that can be perceived by the human ear is from 20 to 20,000 Hz.
Video Encoding
When an image is flashed onto the retina of a human eye, that image is retained for a certain number of milliseconds before fading away. This is one of the unique characteristics of the human eye.
The human eye is not capable of distinguishing between individual images when viewing a series of images that are flashed at a rate of fifty or more images per second.
This concept is used to create moving pictures by all film- and video-based systems for making moving pictures, so it is ubiquitous in the industry.
Video Compression
It is completely impossible to manipulate uncompressed multimedia content such as audio, video, and other types of files in a multimedia editor. It is possible to perform significant compression on the multimedia content.
Over the course of the last few decades, a significant number of computer researchers have contributed to the development of a variety of compression strategies and algorithms that make the transmission of multimedia content possible.
The following are the two algorithms that are required by all compression systems:
- For compressing the multimedia data at the source
- For decompressing the multimedia data at the destination
The two algorithms described above are also referred to as "encoding" and "decoding" algorithms, respectively.
Multimedia Process Scheduling
Operating systems that support multimedia differ from the traditional ones (OSs that don't support multimedia) in the following three ways:
- Process scheduling
- The file system
- Disk scheduling
Let's take a quick look at process scheduling.
Scheduling Homogeneous Process
A video server is considered to be in its most basic form when it is able to support the display of a predetermined number of movies, each of which utilizes the same frame rate, video resolution, data rate, and a few other parameters.
General Real-Time Scheduling
In this model, the number of users can fluctuate as viewers come and go, frame sizes can vary greatly due to the nature of video compression, and different movies can have varying degrees of clarity depending on the resolution. Real-time scheduling refers to the practice of coordinating the start times of multiple concurrent processes, some or all of which have time constraints that need to be satisfied.
Real Monotonic Scheduling
RMS, which stands for rate monotonic scheduling, is a time-tested and tried-and-true static real-time scheduling algorithm for preemptible periodic processes.
The use of rate monotonic scheduling is possible for processes in the event that all five of the following conditions are met:
- Each and every process that occurs on a periodic basis needs to be finished within its period.
- There is no procedure that is reliant on another procedure.
- On each and every burst, each and every process requires the exact same amount of time from the central processing unit.
- There are no due dates for non-periodic processes in general.
- The preemption of a process happens almost instantly and has no overhead.
Earliest Deadline First Scheduling
In its most basic form, the earliest deadline first is a dynamic algorithm because it does not necessitate that the processes be periodic in the same way that the rate monotonic algorithm does. In addition to this, unlike rate monotonic scheduling, it does not necessitate the same amount of run time per central processing unit burst.
Multimedia File System Paradigms
Traditional file systems operate under a unique paradigm as opposed to the one utilized by multimedia file systems.
An open system call must first be made by a process before it can access any file. If the call is successful, the person who made it receives a token of some kind to use in subsequent calls; on the Unix platform, this token is known as a file descriptor, while on the Windows platform, it is called a handle. After reaching this point, the process is able to issue a read system call by passing the token, the address of the buffer, and the byte count as its parameters.
Now that the requested date has been placed in the buffer by the operating system, additional read calls may be made until the process is complete, at which point it will call close to close the file and then return its resources.
File Placement
In general, multimedia files are too large, and while they may only be written once, they can be read multiple times. Furthermore, access to these files typically occurs in sequential order.
The criteria for high quality of service need to be satisfied during the playback of the multimedia files as well. Because of this, the requirements for the multimedia files suggest using different file system layouts than what is typically used by traditional operating systems.
Caching
Traditional LRU file caching doesn't work well with multimedia files because the access patterns for movies are different from those for text files.
The basic concept or idea behind the traditional LRU buffer caches is that after a block is used, it should be kept in the cache for when it is needed again quickly. With multimedia systems, the general access pattern is that a movie is viewed from beginning to end sequentially.
If the user does not rewind the movie in order to watch certain scenes again, it is extremely unlikely that a block will be used more than once. As a direct result of this, the conventional caching strategies are ineffective. Caching, on the other hand, can be useful, but only if it is utilized in a different way.
Disk Scheduling
Multimedia puts different demands on the computer's discs than the traditional textual or text-oriented applications.
Multimedia demands a very high data rate and real-time delivery of the data. Neither of these is trivial to provide.
In the case of a video server, there is an economic pressure to have a single server handle thousands of clients simultaneously.
These requirements have an impact on the whole computer system. Here are the lists of two different kinds of disc scheduling for multimedia:
- Static disk scheduling
- Dynamic disk scheduling
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