Layered coding is a type of

data compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression ...

for

digital video Digital video is an electronic representation of moving visual images (video) in the form of encoded digital data. This is in contrast to analog video, which represents moving visual images in the form of analog signals. Digital video comprises ...

digital audio Digital audio is a representation of sound recorded in, or converted into, digital form. In digital audio, the sound wave of the audio signal is typically encoded as numerical samples in a continuous sequence. For example, in CD audio, sa ...

where the result of compressing the source video data is not just one compressed

data stream In connection-oriented communication, a data stream is the transmission of a sequence of digitally encoded coherent signals to convey information. Typically, the transmitted symbols are grouped into a series of packets. Data streaming has bec ...

, as in other types of compression, but multiple streams, called ''layers'', allowing decompression even if some layers are missing.

Overview

With layered coding, multiple data streams or layers are created when compressing the original video stream. This is in contrast to other types of compression, where the result is typically a single data stream. During decompression, all layers can be combined to recreate the original video stream. Additionally, the stream can be decoded even if some layers are missing (though usually a layer hierarchy has to be respected, with a base layer that must available). If layers are missing, the resulting stream will have reduced visual quality, but will still be usable.

Use cases

Layered coding is helpful when the same video stream needs to be available in different qualities, for example for

adaptive bitrate streaming Adaptive bitrate streaming is a technique used in streaming multimedia over computer networks. While in the past most video or audio streaming technologies utilized streaming protocols such as RTP with RTSP. Today's adaptive streaming technol ...

. Without layered coding, the source video stream must be encoded multiple times to obtain compressed streams with different qualities and bitrates. Layered coding allows only encoding a single time, because streams with different qualities can be obtained by discarding layers.

Related technologies

Layered coding is similar to

multiple description coding Multiple description coding (MDC) in computing is a Channel coding, coding technique that fragments a single Streaming media, media stream into ''n'' substreams (''n'' ≥ 2) referred to as descriptions. The Packet (information technology ...

in that both produce multiple compressed streams that can be combined. However, with multiple description coding the different streams are independent of each other, so any subset can be decoded, providing additional flexibility.

Scalable Video Coding Scalable Video Coding: (SVC) is the name for the Annex G extension of the H.264/MPEG-4 AVC video compression standard. SVC standardizes the encoding of a high-quality video bitstream that also contains one or more subset bitstreams (a form of l ...

is a video compression standard that makes use of layered coding.

References

{{Reflist Data compression

Overview

Use cases

Related technologies

See also

References