Bitrate peeling
Encyclopedia
Bitrate Peeling is a technique used in Ogg
Vorbis
audio encoded streams
, wherein a stream can be encoded
at one bitrate
but can be served at that or any lower bitrate.
Bitrate Peeling is similar in overall effect to Real Networks' technology called "SureStream", which basically creates a single media clip that contains multiple bitrates. The purpose is to provide access to the clip for people with slower Internet
connections, and yet still allow people with faster connection to enjoy the higher quality content. The server
automatically chooses which stream to deliver to the user, depending on user's connection speed.
, Ogg Vorbis bitrate peeling exists only as a concept as there is not yet an encoder capable of producing peelable datastreams http://wiki.xiph.org/Bounties#Ogg_Vorbis_Bitrate_Peeling.
An experimental implementation of bitrate peeling can be found here. However, re-encoding files at a lower bitrate will preserve more quality than this experimental bitrate peeler.
A related technique to the SureStream approach is hierarchical modulation
, used in broadcast, where severally different streams at different qualities (and bitrates) are all broadcast, with the higher quality stream used if possible, with the lower quality streams fallen back on if not.
(Scalable to Lossless), WavPack
, DTS-HD Master Audio
and OptimFROG DualStream.
When a dial-up
user has only about 28 kbit/s of bandwidth
available, the Real
server will serve the 16 kbit/s stream. If the dial-up connection is of higher quality, and maybe about 42 kbit/s is available, the server will automatically switch to the 32 kbit/s stream. A DSL
or Cable
Internet user will be served the 96 kbit/s stream.
This looks good, but even though the user with 28 kbit/s can use a higher bitrate / higher quality stream (maybe 22 to 24 kbit/s), such thing can't be done with SureStream, unless the encoded file contains such a bitrate. This is where Bitrate Peeling comes into play.
An additional feature of Bitrate Peeling is a much finer tuning of available bitrate/quality.
Now, if a dial-up user with 28 kbit/s available bandwidth connects to an Ogg Vorbis file/stream, the server will "peel" the original 96 kbit/s file/stream down to the available bandwidth, the full 28 kbit/s (or 20 to 24 kbit/s, as overhead reduces the effective bandwidth).
This "peeling" process is different from transcoding because transcoding uncompresses the file and recompresses it (a computing-intensive process), whereas the peeling process "cuts the fat" by removing excess bits from the stream without using much processor time.
If 42 kbit/s is available, the server will peel the 96 kbit/s down to the maximum available bandwidth, maybe about 36 to 40 kbit/s.
The benefit of Bitrate Peeling, besides space savings / smaller files, is smaller steps in bitrate and quality, which means that whatever the currently available bandwidth, the streamed file will be of highest bitrate and quality possible for that bandwidth.
These benefits are only theoretical, as the only Vorbis peeler available is still in experimental state and produces file qualities inferior to what transcoding the higher bitrate file to a lower bitrate would.
, JPEG
progressive encoding, and Scalable Video Coding
.
The reason that it is not available in Ogg Vorbis is that current encoders do not organize the code-stream to have progressive accuracy, thus peelers cannot tell which data is more or less important.
See also the Adam7 algorithm
used in PNG interlacing.
Ogg
Ogg is a free, open container format maintained by the Xiph.Org Foundation. The creators of the Ogg format state that it is unrestricted by software patents and is designed to provide for efficient streaming and manipulation of high quality digital multimedia.The Ogg container format can multiplex...
Vorbis
Vorbis
Vorbis is a free software / open source project headed by the Xiph.Org Foundation . The project produces an audio format specification and software implementation for lossy audio compression...
audio encoded streams
Streaming media
Streaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
, wherein a stream can be encoded
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
at one bitrate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
but can be served at that or any lower bitrate.
Bitrate Peeling is similar in overall effect to Real Networks' technology called "SureStream", which basically creates a single media clip that contains multiple bitrates. The purpose is to provide access to the clip for people with slower Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
connections, and yet still allow people with faster connection to enjoy the higher quality content. The server
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
automatically chooses which stream to deliver to the user, depending on user's connection speed.
, Ogg Vorbis bitrate peeling exists only as a concept as there is not yet an encoder capable of producing peelable datastreams http://wiki.xiph.org/Bounties#Ogg_Vorbis_Bitrate_Peeling.
An experimental implementation of bitrate peeling can be found here. However, re-encoding files at a lower bitrate will preserve more quality than this experimental bitrate peeler.
Difference from other technologies
The difference between SureStream and Bitrate Peeling is that SureStream is limited to only a handful of pre-defined bitrates, with significant difference between them, and SureStream encoded files are big because they contain all of the bitrates used, while Bitrate Peeling uses much smaller steps to change the available bitrate and quality, and only the highest bitrate is used to encode the file/stream, which results in smaller files on servers.A related technique to the SureStream approach is hierarchical modulation
Hierarchical modulation
Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed before...
, used in broadcast, where severally different streams at different qualities (and bitrates) are all broadcast, with the higher quality stream used if possible, with the lower quality streams fallen back on if not.
Lossy + Correction
A similar technology is to feature a combination of a lossy format and a lossless correction; this allows stripping the correction to easily obtain a lossy file. Such formats include MPEG-4 SLSMPEG-4 SLS
MPEG-4 SLS, or MPEG-4 Scalable to Lossless as per ISO/IEC 14496-3:2005/Amd 3:2006 , is an extension to the MPEG-4 Part 3 standard to allow lossless audio compression scalable to lossy MPEG-4 General Audio coding methods...
(Scalable to Lossless), WavPack
WavPack
WavPack is a free, open source lossless audio compression format developed by David Bryant.-Features:WavPack compression can compress 8-, 16-, 24-, and 32-bit fixed-point, and 32-bit floating point audio files in the .WAV file format. It also supports surround sound streams and high frequency...
, DTS-HD Master Audio
DTS-HD Master Audio
DTS-HD Master Audio is a lossless audio codec created by Digital Theater System. It was previously known as DTS++. It is an extension of DTS which, when played back on devices which do not support the Master Audio or High Resolution extension, degrades to a "core" track which is lossy. DTS-HD...
and OptimFROG DualStream.
SureStream example
A SureStream encoded file is encoded at bitrates of 16 kbit/s, 32 kbit/s and 96 kbit/s. The file will be about the same in size as three separate files encoded at those bitrates and put together, or one file encoded at the sum of those bitrates, which is about 144 kbit/s (16+32+96).When a dial-up
Dial-up access
Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network to establish a dialled connection to an Internet service provider via telephone lines...
user has only about 28 kbit/s of bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
available, the Real
RealNetworks
RealNetworks, Inc. is a provider of Internet media delivery software and services based in Downtown Seattle, Washington, United States. The company is the creator of RealAudio, a compressed audio format; RealVideo, a compressed video format; RealPlayer, a media player; RealDownloader, a download...
server will serve the 16 kbit/s stream. If the dial-up connection is of higher quality, and maybe about 42 kbit/s is available, the server will automatically switch to the 32 kbit/s stream. A DSL
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
or Cable
Cable modem
A cable modem is a type of network bridge and modem that provides bi-directional data communication via radio frequency channels on a HFC and RFoG infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable Internet, taking advantage of the high...
Internet user will be served the 96 kbit/s stream.
This looks good, but even though the user with 28 kbit/s can use a higher bitrate / higher quality stream (maybe 22 to 24 kbit/s), such thing can't be done with SureStream, unless the encoded file contains such a bitrate. This is where Bitrate Peeling comes into play.
Bitrate Peeling example
Contrary to SureStream, Bitrate Peeling requires only the highest bitrate to be used when encoding a file/stream, which is 96 kbit/s in this case. The obvious benefit is much smaller space on a server required by such a file.An additional feature of Bitrate Peeling is a much finer tuning of available bitrate/quality.
Now, if a dial-up user with 28 kbit/s available bandwidth connects to an Ogg Vorbis file/stream, the server will "peel" the original 96 kbit/s file/stream down to the available bandwidth, the full 28 kbit/s (or 20 to 24 kbit/s, as overhead reduces the effective bandwidth).
This "peeling" process is different from transcoding because transcoding uncompresses the file and recompresses it (a computing-intensive process), whereas the peeling process "cuts the fat" by removing excess bits from the stream without using much processor time.
If 42 kbit/s is available, the server will peel the 96 kbit/s down to the maximum available bandwidth, maybe about 36 to 40 kbit/s.
The benefit of Bitrate Peeling, besides space savings / smaller files, is smaller steps in bitrate and quality, which means that whatever the currently available bandwidth, the streamed file will be of highest bitrate and quality possible for that bandwidth.
These benefits are only theoretical, as the only Vorbis peeler available is still in experimental state and produces file qualities inferior to what transcoding the higher bitrate file to a lower bitrate would.
Comparison with other progressive encodings
Bitrate peeling is theoretically possible, and is implemented in some other formats, notably JPEG 2000JPEG 2000
JPEG 2000 is an image compression standard and coding system. It was created by the Joint Photographic Experts Group committee in 2000 with the intention of superseding their original discrete cosine transform-based JPEG standard with a newly designed, wavelet-based method...
, JPEG
JPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
progressive encoding, and Scalable Video Coding
Scalable Video Coding
Scalable Video Coding 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 subset video bitstream is derived by dropping packets from the...
.
The reason that it is not available in Ogg Vorbis is that current encoders do not organize the code-stream to have progressive accuracy, thus peelers cannot tell which data is more or less important.
See also the Adam7 algorithm
Adam7 algorithm
Adam7 is an interlacing algorithm for raster images, best known as the interlacing scheme optionally used in PNG images. An Adam7 interlaced image is broken into seven subimages, which are defined by replicating this 8×8 pattern across the full image....
used in PNG interlacing.
See also
- OggOggOgg is a free, open container format maintained by the Xiph.Org Foundation. The creators of the Ogg format state that it is unrestricted by software patents and is designed to provide for efficient streaming and manipulation of high quality digital multimedia.The Ogg container format can multiplex...
bitstream format - VorbisVorbisVorbis is a free software / open source project headed by the Xiph.Org Foundation . The project produces an audio format specification and software implementation for lossy audio compression...
, a freeGratisGratis is the process of providing goods or services without compensation. It is often referred to in English as "free of charge" or "complimentary"...
audio compression codecCodecA codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"... - Streaming mediaStreaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
- audio file formatAudio file formatAn audio file format is a file format for storing digital audio data on a computer system. This data can be stored uncompressed, or compressed to reduce the file size. It can be a raw bitstream, but it is usually a container format or an audio data format with defined storage layer.-Types of...
- audio signal processingAudio signal processingAudio signal processing, sometimes referred to as audio processing, is the intentional alteration of auditory signals, or sound. As audio signals may be electronically represented in either digital or analog format, signal processing may occur in either domain...
- audio storage
- codecCodecA codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...
- data compressionData compressionIn computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
External links
- Xiph.org Foundation
- Xiph.org Bitrate Peeling Bounty
- Ogg Vorbis site
- Ogg Vorbis Bitrate Peeling Description
- An experimental Ogg vorbis Bitrate Peeler