DOCSLIB.ORG

Low-Delay, Low-Power, and Real-Time Audio Remote Transmission System Over Wi-Fi

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Low-Delay, Low-Power, and Real-Time Audio Remote Transmission System Over Wi-Fi J. lnf. Commun. Converg. Eng. 18(2): 115-122, Jun. 2020 Regular paper Low-Delay, Low-Power, and Real-Time Audio Remote Transmission System over Wi-Fi Jinwoo Hong1* , Jeongju Yoo2, and Jeongkyu Hong3, Member, KIICE 1Media Research Division, Electronics and Telecommunications Research Institute, Daejeon 34129, Republic of Korea 2Radio & Satellite Division, Electronics and Telecommunications Research Institute, Daejeon 34129, Republic of Korea 3Department of Computer Engineering, Yeungnam University, Gyeongsan 38541, Republic of Korea Abstract Audiovisual (AV) facilities such as TVs and signage are installed in various public places. However, audio cannot be used to prevent noise and interference from individuals, which results in a loss of concentration and understanding of AV content. To address this problem, a total technique for remotely listening to audio from audiovisual facilities with clean sound quality while maintaining video and lip-syncing through personal smart mobile devices is proposed in this paper. Through the experimental results, the proposed scheme has been verified to reduce system power consumption by 8% to 16% and provide real-time processing with a low latency of 120 ms. The system described in this paper will contribute to the activation of audio tele- hearing services as it is possible to provide audio remote services in various places, such as express buses, trains, wide-area and intercity buses, public waiting rooms, and various application services. Index Terms: Wi-Fi audio, Audio remote transmission, Low power consumption, Low-delay audio I. INTRODUCTION hearing is always open and recognizes sound information regardless of intention. Of course, it is possible to listen to a Many types of public transportation and places such as specific sound selectively among various sounds, but this has high-speed buses, trains, and waiting rooms have audiovisual several drawbacks, such as different sounds being heard (AV) facilities that play videos to relieve the boredom of together and requiring intense concentration which can tire users caused by long waiting and/or traveling times. How- the listener [1]. ever, their audio is very low or muted to allow for individual To provide a comfortable audio environment for users preference and restriction of noise, which interferes with nat- without creating excessive noise in public spaces, this paper ural listening. As a result, users cannot enjoy AV content proposes a low-power and low-delay remote audio transmis- properly because their concentration and understanding of sion system. The proposed technique converts the received the content is reduced. This situation is apparent especially analog audio (or digital audio) output from the AV facilities in hospital rooms with two or more patients, families with to digital audio, compresses it, and then transmits it with low students, crowded tourist spots, digital signs in public places, latency via Wi-Fi, thereby achieving real-time transmission. restaurants, and cafes. This allows individuals to remotely listen to the audio of the This is a result of hearing openness, one of the characteris- target video using their smart mobile devices such as smart- tics of the human hearing mechanism. Specifically, human phones, tablets, laptops, and smartwatches. Received 07 May 2020, Revised 22 June 2020, Accepted 22 June 2020 *Corresponding Author Jinwoo Hong (E-mail: [email protected], Tel: +82-42-860-6260) Media Research Division, Electronics and Telecommunications Research Institute, Daejeon 34129, Republic of Korea. https://doi.org/10.6109/jicce.2020.18.2.115 print ISSN: 2234-8255 online ISSN: 2234-8883 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by- nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Copyright ⓒ The Korea Institute of Information and Communication Engineering 115 J. lnf. Commun. Converg. Eng. 18(2): 115-122, Jun. 2020 The proposed Wi-Fi based audio remote transmission sys- tem provides real-time playback within a 120 ms latency to maintain synchronization between the video and audio played on the AV facilities. In addition, our system adopts data reliability technology to reduce memory power con- sumption and ensure high-performance computing. We tested our proposed system on 304 people by implementing it in a real environment and achieved an average score of 4.37 out of 5.0, which verifies the quality and convenience of the pro- Fig. 1. Audio remote transmission system diagram. posed system. Similar products, such as Bluetooth which uses radiofre- quency and wireless headphones, are available; however, hours per day, technical considerations to minimize they necessitate dedicated transmission and reception their power consumption should be investigated [7]. devices and do not allow multiple users to access the target 7) Up to 40 users should be able to send and receive AV facilities simultaneously [2]. Conversely, our system remote audio simultaneously. offers a service at a low price by using a smartphone as the 8) The system must provide a real-time protocol (RTP) receiving device, allows up to 40 users to access a single AV including a Wi-Fi access point (AP) function and for- facility concurrently, enables a specific facility device from ward error correction (FEC) function in the unicast and multiple devices to be selected, and can provide various broadcast mode [8-10]. additional services through the smartphone screen while Fig. 1 shows the proposed audio remote transmission sys- using our audio transmission service. tem, which satisfies all eight requirements described above, In this paper, Section 2 describes the system design and consisting of two modules. The first is an audio remote implementation issues of the proposed remote audio trans- transmission module (ARTM) which transmits the AV facil- mission system and Section 3 explains the various experi- ity’s audio output via Wi-Fi and the other is an audio play- mental results and verification details. Finally, conclusions back module (APM) which renders the received audio on are included in Section 4. users’ smart devices. Using a user’s existing smart device as an APM does not require dedicated hardware (HW) and can provide a remote audio transmission service using only the II. DESIGN AND IMPLEMENTATION OF AUDIO audio playback application and the device’s Wi-Fi capability. REMOTE TRANSMISSION SYSTEM B. ARTM Design and Implementation A. System Requirements and Concept An ARTM consists of a remote transmission controller to Several technical factors affect the way in which audio can support a transmission function as shown in Fig. 2. ARTM be listened to remotely from AV facilities. However, to apply converts analog audio signals from AV facilities into digital the most convenient and efficient method for the user and signals. The digital signals are then compressed in real time system requirements, we first derive the following character- and transmitted over Wi-Fi via an RTP-FEC stream. istics. Especially, the audio remote TX service controller consists 1) The audio quality at a remote position must be main- of five parts, as shown in Fig. 3. The functions of each part tained at 64 kbps or higher to satisfy the MP3 audio are shown in Table 1. In the ARTM, audio input is received standard [3]. through a sound device driver and the received data are com- 2) The maximum delay time should be less than 150 ms to pressed in a format suitable for transmission, which are then maintain lip-syncing between the video playback and remote audio of the AV facilities [4, 5]. 3) The audio remote service must be processed in real time without interruption of transmission and reception processing [6]. 4) By using the users’ smart devices, the system prevents users from incurring extra costs due to purchasing addi- tional hardware or audio playback software (SW). 5) The system provides a free audio playback application that uses a high-quality open audio codec. 6) Since the target facilities are usually operated for 24 Fig. 2. ARTM configuration diagram. https://doi.org/10.6109/jicce.2020.18.2.115 116 Low-Delay, Low-Power, and Real-Time Audio Remote Transmission System over Wi-Fi receiving audio from smart devices. C. APM Design and Implementation The APM functionality consists of checking for errors with RTP-FEC, restoring the signals received over Wi-Fi as Fig. 3. Audio remote transmission service controller. shown in Fig. 5, and then converting the signals from digital to analog and printing via SW operation. Table 1. Parts functions of the audio TX service controller The audio remote RX service controller in Fig. 5 includes Parts Major Function the functions of the four parts shown in Fig. 6. Table 2 lists Initialization/start/stop/restart control of audio Service Manager the functions of each part. remote transmission service SW, which operates on the APM, is implemented as apps Management of service target facility list using TCP that could be installed on both the iOS and Android plat- Session Manager socket connection/release over smart device in uni- forms and provides the ability to search for all APs of AV cast mode facilities installed in the vicinity, and to automatically set up Encoder type setting and control for compressing of Encoder I/F networks using a dynamic host configuration protocol audio data (DHCP). RTP Streamer setting and control, valid FEC setting Streamer I/F and packet generation according to Wi-Fi status in multicast mode D. Implementation of Audio Compression Technology Storage/management/transmission control for added Added Info. I/F information data To compress and restore audio to ARTM and APM, the Internet engineering task force (IETF) standardized (RFC 6716) and developed Opus codecs were used. Opus is an provided in the form of an appropriate library that can be open audio codec that is accessible to anyone at no extra used in the receiving application of the smart devices.
Load more

Recommended publications
  • Fast Cosine Transform to Increase Speed-Up and Efficiency of Karhunen-Loève Transform for Lossy Image Compression
    Fast Cosine Transform to increase speed-up and efficiency of Karhunen-Loève Transform for lossy image compression Mario Mastriani, and Juliana Gambini Several authors have tried to combine the DCT with the Abstract —In this work, we present a comparison between two KLT but with questionable success [1], with particular interest techniques of image compression. In the first case, the image is to multispectral imagery [30, 32, 34]. divided in blocks which are collected according to zig-zag scan. In In all cases, the KLT is used to decorrelate in the spectral the second one, we apply the Fast Cosine Transform to the image, domain. All images are first decomposed into blocks, and each and then the transformed image is divided in blocks which are collected according to zig-zag scan too. Later, in both cases, the block uses its own KLT instead of one single matrix for the Karhunen-Loève transform is applied to mentioned blocks. On the whole image. In this paper, we use the KLT for a decorrelation other hand, we present three new metrics based on eigenvalues for a between sub-blocks resulting of the applications of a DCT better comparative evaluation of the techniques. Simulations show with zig-zag scan, that is to say, in the spectral domain. that the combined version is the best, with minor Mean Absolute We introduce in this paper an appropriate sequence, Error (MAE) and Mean Squared Error (MSE), higher Peak Signal to decorrelating first the data in the spatial domain using the DCT Noise Ratio (PSNR) and better image quality.
    [Show full text]
  • Image Compression Using DCT and Wavelet Transformations
    International Journal of Signal Processing, Image Processing and Pattern Recognition Vol. 4, No. 3, September, 2011 Image Compression Using DCT and Wavelet Transformations Prabhakar.Telagarapu, V.Jagan Naveen, A.Lakshmi..Prasanthi, G.Vijaya Santhi GMR Institute of Technology, Rajam – 532 127, Srikakulam District, Andhra Pradesh, India. [email protected], [email protected], [email protected], [email protected] Abstract Image compression is a widely addressed researched area. Many compression standards are in place. But still here there is a scope for high compression with quality reconstruction. The JPEG standard makes use of Discrete Cosine Transform (DCT) for compression. The introduction of the wavelets gave a different dimensions to the compression. This paper aims at the analysis of compression using DCT and Wavelet transform by selecting proper threshold method, better result for PSNR have been obtained. Extensive experimentation has been carried out to arrive at the conclusion. Keywords:. Discrete Cosine Transform, Wavelet transform, PSNR, Image compression 1. Introduction Compressing an image is significantly different than compressing raw binary data. Of course, general purpose compression programs can be used to compress images, but the result is less than optimal. This is because images have certain statistical properties which can be exploited by encoders specifically designed for them. Also, some of the finer details in the image can be sacrificed for the sake of saving a little more bandwidth or storage space. This also means that lossy compression techniques can be used in this area. Uncompressed multimedia (graphics, audio and video) data requires considerable storage capacity and transmission bandwidth. Despite rapid progress in mass-storage density, processor speeds, and digital communication system performance, demand for data storage capacity and data- transmission bandwidth continues to outstrip the capabilities of available technologies.
    [Show full text]
  • Analysis of Image Compression Algorithm Using
    IJSTE - International Journal of Science Technology & Engineering | Volume 3 | Issue 12 | June 2017 ISSN (online): 2349-784X Analysis of Image Compression Algorithm using DCT Aman George Ashish Sahu Student Assistant Professor Department of Information Technology Department of Information Technology SSTC, SSGI, FET Junwani, Bhilai - 490020, Chhattisgarh Swami Vivekananda Technical University, India Durg, C.G., India Abstract Image compression means reducing the size of graphics file, without compromising on its quality. Depending on the reconstructed image, to be exactly same as the original or some unidentified loss may be incurred, two techniques for compression exist. This paper presents DCT implementation because these are the lossy techniques. Image compression is the application of Data compression on digital images. The discrete cosine transform (DCT) is a technique for converting a signal into elementary frequency components. Image compression algorithm was comprehended using Matlab code, and modified to perform better when implemented in hardware description language. The IMAP block and IMAQ block of MATLAB was used to analyse and study the results of Image Compression using DCT and varying co-efficients for compression were developed to show the resulting image and error image from the original images. The original image is transformed in 8-by-8 blocks and then inverse transformed in 8-by-8 blocks to create the reconstructed image. Image Compression is specially used where tolerable degradation is required. This paper is a survey for lossy image compression using Discrete Cosine Transform, it covers JPEG compression algorithm which is used for full-colour still image applications and describes all the components of it.
    [Show full text]
  • Telestream Cloud High Quality Video Encoding Service in the Cloud
    Telestream Cloud High quality video encoding service in the cloud Telestream Cloud is a high quality, video encoding software-as-a-service (SaaS) in the cloud, offering fast and powerful encoding for your workflow. Telestream Cloud pricing is structured as pay-as-you-go monthly subscriptions for quick scaling as your workflow changes with no upfront expenses. Who uses Telestream Cloud? Telestream Cloud’s elegantly simple user interface scales quickly and seamlessly for media professionals who utilize video transcoding heavily in their business like: ■ Advertising agencies ■ On-line broadcasters ■ Gaming ■ Entertainment ■ OTT service provider for media streaming ■ Boutique post production studios For content creators and video producers, Telestream Cloud encoding cloud service is pay-as-you-go, and allows you to collocate video files with your other cloud services across multiple cloud storage options. The service provides high quality output in most formats to meet the needs of: ■ Small businesses ■ Houses of worship ■ Digital marketing ■ Education ■ Nonprofits Telestream Cloud provides unlimited scalability to address peak demand times and encoding requirements for large files for video pros who work in: ■ Broadcast networks ■ Broadcast news or sports ■ Cable service providers ■ Large post-production houses Telestream Cloud is a complementary service to the Vantage platform. During peak demand times, Cloud service can offset the workload. The service also allows easy collaboration of projects across multiple sites or remote locations. Why choose Telestream Cloud? The best video encoding quality for all formats & codecs: An extensive set of encoding profiles built-in for all major formats to ensure the output is optimized for the highest quality.
    [Show full text]
  • Conference Paper
    International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXIV-5/W10 Accurate 3D information extraction from large-scale data compressed image and the study of the optimum stereo imaging method Riichi NAGURA*, *Kanagawa Institute of Technology [email protected] KEY WORDS: High Resolution Imaging, Data compression, Height information extraction, Remote Sensing ABSTRACT The paper reports the accurate height information extraction method under the condition of large-scale compressed images, and proposes the optimum stereo imaging system using the multi-directional imaging and the time delay integration method. Recently, the transmission data rate of stereo images have increased enormously accompany by the progress of high- resolution imaging. Then, the large-scale data compression becomes indispensable, especially in the case of the data transmission from satellite. In the early stages the lossless compression was used, however the data-rate of the lossless compression image is not sufficiently small. Then, this paper mainly discusses the effects of lossy compression methods. First, the paper describes the effects for JPEG compression method using DCT, and next analyzes the effects for JPEG2000 compression method using wavelet transform. The paper also indicates the effects of JPEG-LS compression method. The correlative detection techniques are used in these analyses. As the results, JPEG2000 is superior to former JPEG as foreseeing, however the bit error affects in many vicinity pixels in the large-scale compression. Then, the correction of the bit error becomes indispensable. The paper reports the results of associating Turbo coding techniques with the compressed data, and consequently, the bit error can be vanished sufficiently even in the case of noisy transmission path.
    [Show full text]
  • Discrete Cosine Transformation Based Image Data Compression Considering Image Restoration
    (IJACSA) International Journal of Advanced Computer Science and Applications, Vol. 11, No. 6, 2020 Discrete Cosine Transformation based Image Data Compression Considering Image Restoration Kohei Arai Graduate School of Science and Engineering Saga University, Saga City Japan Abstract—Discrete Cosine Transformation (DCT) based restored image and the original image not on the space of the image data compression considering image restoration is original image but on the observed image. A general inverse proposed. An image data compression method based on the filter, a least-squares filter with constraints, and a projection compression (DCT) featuring an image restoration method is filter and a partial projection filter that may be significantly proposed. DCT image compression is widely used and has four affected by noise in the restored image have been proposed [2]. major image defects. In order to reduce the noise and distortions, However, the former is insufficient for optimization of the proposed method expresses a set of parameters for the evaluation criteria, etc., and is under study. assumed distortion model based on an image restoration method. The results from the experiment with Landsat TM (Thematic On the other hand, the latter is essentially a method for Mapper) data of Saga show a good image compression finding a non-linear solution, so it can take only a method performance of compression factor and image quality, namely, based on an iterative method, and various methods based on the proposed method achieved 25% of improvement of the iterative methods have been tried. There are various iterative compression factor compared to the existing method of DCT with methods, but there are a stationary iterative method typified by almost comparable image quality between both methods.
    [Show full text]
  • A Lossy Colour Image Compression Using Integer Wavelet Transforms and Binary Plane Transform
    Global Journal of Computer Science and Technology Graphics & Vision Volume 12 Issue 15 Version 1.0 Year 2012 Type: Double Blind Peer Reviewed International Research Journal Publisher: Global Journals Inc. (USA) Online ISSN: 0975-4172 & Print ISSN: 0975-4350 A Lossy Colour Image Compression Using Integer Wavelet Transforms and Binary Plane Technique By P.Ashok Babu & Dr. K.V.S.V.R.Prasad Narsimha Reddy Engineering College Hyderabad, AP, India Abstract - In the recent period, image data compression is the major component of communication and storage systems where the uncompressed images requires considerable compression technique, which should be capable of reducing the crippling disadvantages of data transmission and image storage. In the research paper, the novel image compression technique is proposed which is based on the spatial domain which is quite effective for the compression of images. However, the performance of the proposed methodology is compared with the conventional compression techniques (Joint Photographic Experts Group) JPEG and set partitioning in hierarchical trees (SPIHT) using the evaluation metrics compression ratio and peak signal to noise ratio. It is evaluated that Integer wavelets with binary plane technique is more effective compression technique than JPEG and SPIHT as it provides more efficient quality metrics values and visual quality. GJCST-F Classification: I.4.2 A Lossy Colour Image Compression Using Integer Wavelet Transforms and Binary Plane Transform Strictly as per the compliance and regulations of: © 2012. P.Ashok Babu & Dr. K.V.S.V.R.Prasad. This is a research/review paper, distributed under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported License http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, distribution, and reproduction inany medium, provided the original work is properly cited.
    [Show full text]
  • Advanced Master in Space Communications Systems PROJECT 1 : DATA COMPRESSION APPLIED to IMAGES Maël Barthe & Arthur Louchar
    Advanced Master in Space Communications Systems PROJECT 1 : DATA COMPRESSION APPLIED TO IMAGES Maël Barthe & Arthur Louchart Project 1 : Data compression applied to images Supervised by M. Tarik Benaddi Special thanks to : Lenna Sjööblom In the early seventies, an unknown researcher at the University of Southern California working on compression technologies scanned in the image of Lenna Sjööblom centerfold from Playboy magazine (playmate of the month November 1972). Since that time, images of the Playmate have been used as the industry standard for testing ways in which pictures can be manipulated and transmitted electronically. Over the past 25 years, no image has been more important in the history of imaging and electronic communications. Because of the ubiquity of her Playboy photo scan, she has been called the "first lady of the internet". The title was given to her by Jeff Seideman in a press release he issued announcing her appearance at the 50th annual IS&T Conference (Imaging Science & Technology). This project is dedicated to Lenna. 1 Project 1 : Data compression applied to images Supervised by M. Tarik Benaddi Table of contents INTRODUCTION ............................................................................................................................................. 3 1. WHAT IS DATA COMPRESSION? .......................................................................................................................... 4 1.1. Definition ..........................................................................................................................................
    [Show full text]
  • A Survey of Compression Techniques
    International Journal of Recent Technology and Engineering (IJRTE) ISSN: 2277-3878, Volume-2 Issue-1 March 2013 A Survey of Compression Techniques Sashikala, Melwin .Y., Arunodhayan Sam Solomon, M.N.Nachappa Abstract - Digital data is owned, used and enjoyed by many reducing the file size without affecting the quality of the people all over the world. Compressing data is mostly done when original Data. Data Compression is an important part of we face with problems of constraints in memory. In this paper we Computer Science mainly because of the reduced data have attempted to discuss in general about compression and decompression, the different techniques of compression using communication and the Storage cost. [1] digital data is ‘Lossless method compression and decompression’ on text data usually created by a word processor as text data, a digital using a simple coding technique called Huffmann coding. camera to capture pictures of audio and video data, a scanner Index Words: Lossless text data compression, Huffman to scan documents of text as image data or other devices, once coding. the data is captured it is edited on a computer, then stored on a optical medium or disk permanently based on the users need, sharing information Compressed data can be I. INTRODUCTION transmitted through e-mail, and downloaded. In 1838 morse code used data compression for telegraphy which was based on using shorter code words for letters such II. COMPRESSION as "e" and "t" that are more common in English . Modern Compression is a technology by which one or more files or work on data compression began in the late 1940s with the directories size can be reduced so that it is easy to handle.
    [Show full text]
  • Compression of Vc Shares
    International Journal of Computational Science and Information Technology (IJCSITY) Vol.4,No.1,February 2016 COMPRESSION OF VC SHARES M. Mary Shanthi Rani 1 and G. Germine Mary 2 1Department of Computer Science and Application, Gandhigram Rural Institute-Deemed University, Gandhigram-624302, Tamil Nadu, India 2Department of Computer Science, Fatima College,Madurai – 625016, Tamil Nadu, India. ABSTRACT Visual Cryptography (VC) schemes conceal the secret image into two or more images which are called shares. The secret image can be recovered simply by stacking the shares together.In VC the reconstructed image after decryption process encounter a major problem of Pixel expansion. This is overcome in this proposed method by minimizing the memory size using lossless image compression techniques. The shares are compressed using Vector Quantization followed by Run Length Encoding methods and are converted to few bits. Decompression is done by applying decoding procedure and the shares are overlapped to view the secret image. KEYWORDS Secret Image Sharing, Visual Cryptography, Image Compression, Vector Quantization, Run Length Encoding. 1.INTRODUCTION In recent years, along with the prevalent advancements in image processing, secret image sharing also has been in active research. Secret Image Sharing refers to a method for distributing a secret image amongst a group of participants, each of whom is allocated a share of the secret. The secret can be reconstructed only when a sufficient number of shares are combined together; individual shares are of no use on their own. A special type of Secret Sharing Scheme known as Visual Cryptography was proposed in 1994 by Naor and Shamir [1].
    [Show full text]
  • Weather Radar Data Compression Based on Spatial and Temporal Prediction
    atmosphere Article Weather Radar Data Compression Based on Spatial and Temporal Prediction Qiangyu Zeng 1,2,*, Jianxin He 1,2, Zhao Shi 1,2 and Xuehua Li 1,2 1 College of Electronic Engineering, Chengdu University of Information Technology, Chengdu 610225, China; [email protected] (J.H.); [email protected] (Z.S.); [email protected] (X.L.) 2 CMA Key Laboratory of Atmospheric Sounding, Chengdu 610225, China * Correspondence: [email protected]; Tel.: +86-28-8596-7291 Received: 6 February 2018; Accepted: 6 March 2018; Published: 8 March 2018 Abstract: The transmission and storage of weather radar products will be an important problem for future weather radar applications. The aim of this work is to provide a solution for real-time transmission of weather radar data and efficient data storage. By upgrading the capabilities of radar, the amount of data that can be processed continues to increase. Weather radar compression is necessary to reduce the amount of data for transmission and archiving. The characteristics of weather radar data are not considered in general-purpose compression programs. The sparsity and data redundancy of weather radar data are analyzed. A lossless compression of weather radar data based on prediction coding is presented, which is called spatial and temporal prediction compression (STPC). The spatial and temporal correlations in weather radar data are utilized to improve the compression ratio. A specific prediction scheme for weather radar data is given, while the residual data and motion vectors are used to replace the original values for entropy coding. After this, the Level-II product from CINRAD SA is used to evaluate STPC.
    [Show full text]
  • What Is a Codec?
    What is a Codec? Codec is a portmanteau of either "Compressor-Decompressor" or "Coder-Decoder," which describes a device or program capable of performing transformations on a data stream or signal. Codecs encode a stream or signal for transmission, storage or encryption and decode it for viewing or editing. Codecs are often used in videoconferencing and streaming media solutions. A video codec converts analog video signals from a video camera into digital signals for transmission. It then converts the digital signals back to analog for display. An audio codec converts analog audio signals from a microphone into digital signals for transmission. It then converts the digital signals back to analog for playing. The raw encoded form of audio and video data is often called essence, to distinguish it from the metadata information that together make up the information content of the stream and any "wrapper" data that is then added to aid access to or improve the robustness of the stream. Most codecs are lossy, in order to get a reasonably small file size. There are lossless codecs as well, but for most purposes the almost imperceptible increase in quality is not worth the considerable increase in data size. The main exception is if the data will undergo more processing in the future, in which case the repeated lossy encoding would damage the eventual quality too much. Many multimedia data streams need to contain both audio and video data, and often some form of metadata that permits synchronization of the audio and video. Each of these three streams may be handled by different programs, processes, or hardware; but for the multimedia data stream to be useful in stored or transmitted form, they must be encapsulated together in a container format.
    [Show full text]