When a user with a low bitrate codec talks to a user with another codec, additional distortion is introduced by each transcoding.Īudio Video Interleave (AVI) is sometimes erroneously described as a codec, but AVI is actually a container format, while a codec is a software or hardware tool that encodes or decodes audio or video into or from some audio or video format. Other codecs may not make those same assumptions. Beyond the initial increase in distortion, lower bit rate codecs also achieve their lower bit rates by using more complex algorithms that make certain assumptions, such as those about the media and the packet loss rate. Lower bitrate codecs allow more users, but they also have more distortion. Each of these three streams may be handled by different programs, processes, or hardware but for the multimedia data streams to be useful in stored or transmitted form, they must be encapsulated together in a container format. Many multimedia data streams contain both audio and video, and often some metadata that permits synchronization of audio and video.
aiff file) has long been a standard across multiple platforms, but its transmission over networks is slow and expensive compared with more modern compressed formats, such as Opus and MP3. For example, raw uncompressed PCM audio (44.1 kHz, 16 bit stereo, as represented on an audio CD or in a.
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The older formats are often ill-suited to modern applications, however, such as playback in small portable devices. The impact is lessened for older formats, for which free or nearly-free codecs have existed for a long time. This variety of codecs can create compatibility and obsolescence issues. There are thousands of audio and video codecs, ranging in cost from free to hundreds of dollars or more. In contrast, audio codecs for recording or broadcast can use high-latency audio compression techniques to achieve higher fidelity at a lower bit-rate. For example, a digital video (using a DV codec) of a sports event needs to encode motion well but not necessarily exact colors, while a video of an art exhibit needs to encode color and surface texture well.Īudio codecs for cell phones need to have very low latency between source encoding and playback. Codecs are often designed to emphasize certain aspects of the media to be encoded. Two principal techniques are used in codecs, pulse-code modulation and delta modulation. over the internet.įurther information: Video codec and Audio codec Lower data rates also reduce cost and improve performance when the data is transmitted, e.g. Smaller data sets ease the strain on relatively expensive storage sub-systems such as non-volatile memory and hard disk, as well as write-once-read-many formats such as CD-ROM, DVD and Blu-ray Disc. The most widely used lossy data compression technique in digital media is based on the discrete cosine transform (DCT), used in compression standards such as JPEG images, H.26x and MPEG video, and MP3 and AAC audio. Often, this type of compression is virtually indistinguishable from the original uncompressed sound or images, depending on the codec and the settings used. They reduce quality in order to maximize compression. The decreasing cost of storage capacity and network bandwidth has a tendency to reduce the need for lossy codecs for some media. Using more than one codec or encoding scheme successively can also degrade quality significantly. This is especially true if the data is to undergo further processing (for example editing) in which case the repeated application of processing (encoding and decoding) on lossy codecs will degrade the quality of the resulting data such that it is no longer identifiable (visually, audibly or both). If preserving the original quality of the stream is more important than eliminating the correspondingly larger data sizes, lossless codecs are preferred.
Lossless codecs are often used for archiving data in a compressed form while retaining all information present in the original stream. Compression codecs are classified primarily into lossy codecs and lossless codecs. In addition to encoding a signal, a codec may also compress the data to reduce transmission bandwidth or storage space. Further information: Image compression, Video coding format, and Audio coding format
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