Variable bitrate (VBR) is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate (CBR), VBR files vary the amount of output data per time segment. VBR allows a higher bitrate (and therefore more storage space) to be allocated to the more complex segments of media files while less space is allocated to less complex segments. The average of these rates can be calculated to produce an average bitrate for the file.
The advantages of VBR are that it produces a better quality-to-space ratio compared to a CBR file of the same data. The bits available are used more flexibly to encode the sound or video data more accurately, with fewer bits used in less demanding passages and more bits used in difficult-to-encode passages.[2][4]
The disadvantages are that it may take more time to encode, as the process is more complex, and that some hardware might not be compatible with VBR files.[2]
Methods of VBR encodingedit
Multi-pass encoding and single-pass encodingedit
VBR is created using so-called single-pass encoding or multi-pass encoding. Single-pass encoding analyzes and encodes the data "on the fly" and it is also used in constant bitrate encoding. Single-pass encoding is used when the encoding speed is most important — e.g. for real-time encoding. Single-pass VBR encoding is usually controlled by the fixed quality setting or by the bitrate range (minimum and maximum allowed bitrate) or by the average bitrate setting. Multi-pass encoding is used when the encoding quality is most important. Multi-pass encoding cannot be used in real-time encoding, live broadcast or live streaming. Multi-pass encoding takes much longer than single-pass encoding, because every pass means one pass through the input data (usually through the whole input file). Multi-pass encoding is used only for VBR encoding, because CBR encoding doesn't offer any flexibility to change the bitrate. The most common multi-pass encoding is two-pass encoding. In the first pass of two-pass encoding, the input data is being analyzed and the result is stored in a log file. In the second pass, the collected data from the first pass is used to achieve the best encoding quality. In a video encoding, two-pass encoding is usually controlled by the average bitrate setting or by the bitrate range setting (minimal and maximal allowed bitrate) or by the target video file size setting.[5][6]
Bitrate rangeedit
This VBR encoding method allows the user to specify a bitrate range — a minimum and/or maximum allowed bitrate.[7] Some encoders extend this method with an average bitrate. The minimum and maximum allowed bitrate set bounds in which the bitrate may vary. The disadvantage of this method is that the average bitrate (and hence file size) will not be known ahead of time. The bitrate range is also used in some fixed quality encoding methods, but usually without permission to change a particular bitrate.[8]
Average bitrateedit
The disadvantage of single pass ABR encoding (with or without Constrained Variable Bitrate) is the opposite of fixed quantizer VBR — the size of the output is known ahead of time, but the resulting quality is unknown, although still better than CBR.[9]
The multi-pass ABR encoding is more similar to fixed quantizer VBR, because a higher average will really increase the quality.[10]
File sizeedit
VBR encoding using the file size setting is usually multi-pass encoding. It allows the user to specify a specific target file size. In the first pass, the encoder analyzes the input file and automatically calculates possible bitrate range and/or average bitrate. In the last pass, the encoder distributes the available bits among the entire video to achieve uniform quality.[10]
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January 01, 1970
variable, bitrate, term, used, telecommunications, computing, that, relates, bitrate, used, sound, video, encoding, opposed, constant, bitrate, files, vary, amount, output, data, time, segment, allows, higher, bitrate, therefore, more, storage, space, allocate. Variable bitrate VBR is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding As opposed to constant bitrate CBR VBR files vary the amount of output data per time segment VBR allows a higher bitrate and therefore more storage space to be allocated to the more complex segments of media files while less space is allocated to less complex segments The average of these rates can be calculated to produce an average bitrate for the file MP3 WMA and AAC audio files can optionally be encoded in VBR while Opus and Vorbis are encoded in VBR by default 1 2 3 Variable bit rate encoding is also commonly used on MPEG 2 video MPEG 4 Part 2 video Xvid DivX etc MPEG 4 Part 10 H 264 video Theora Dirac and other video compression formats citation needed Additionally variable rate encoding is inherent in lossless compression schemes such as FLAC and Apple Lossless citation needed Contents 1 Advantages and disadvantages of VBR 2 Methods of VBR encoding 2 1 Multi pass encoding and single pass encoding 2 2 Bitrate range 2 3 Average bitrate 2 4 File size 3 See also 4 ReferencesAdvantages and disadvantages of VBR editThe advantages of VBR are that it produces a better quality to space ratio compared to a CBR file of the same data The bits available are used more flexibly to encode the sound or video data more accurately with fewer bits used in less demanding passages and more bits used in difficult to encode passages 2 4 The disadvantages are that it may take more time to encode as the process is more complex and that some hardware might not be compatible with VBR files 2 Methods of VBR encoding editMulti pass encoding and single pass encoding edit VBR is created using so called single pass encoding or multi pass encoding Single pass encoding analyzes and encodes the data on the fly and it is also used in constant bitrate encoding Single pass encoding is used when the encoding speed is most important e g for real time encoding Single pass VBR encoding is usually controlled by the fixed quality setting or by the bitrate range minimum and maximum allowed bitrate or by the average bitrate setting Multi pass encoding is used when the encoding quality is most important Multi pass encoding cannot be used in real time encoding live broadcast or live streaming Multi pass encoding takes much longer than single pass encoding because every pass means one pass through the input data usually through the whole input file Multi pass encoding is used only for VBR encoding because CBR encoding doesn t offer any flexibility to change the bitrate The most common multi pass encoding is two pass encoding In the first pass of two pass encoding the input data is being analyzed and the result is stored in a log file In the second pass the collected data from the first pass is used to achieve the best encoding quality In a video encoding two pass encoding is usually controlled by the average bitrate setting or by the bitrate range setting minimal and maximal allowed bitrate or by the target video file size setting 5 6 Bitrate range edit This VBR encoding method allows the user to specify a bitrate range a minimum and or maximum allowed bitrate 7 Some encoders extend this method with an average bitrate The minimum and maximum allowed bitrate set bounds in which the bitrate may vary The disadvantage of this method is that the average bitrate and hence file size will not be known ahead of time The bitrate range is also used in some fixed quality encoding methods but usually without permission to change a particular bitrate 8 Average bitrate edit The disadvantage of single pass ABR encoding with or without Constrained Variable Bitrate is the opposite of fixed quantizer VBR the size of the output is known ahead of time but the resulting quality is unknown although still better than CBR 9 The multi pass ABR encoding is more similar to fixed quantizer VBR because a higher average will really increase the quality 10 File size edit VBR encoding using the file size setting is usually multi pass encoding It allows the user to specify a specific target file size In the first pass the encoder analyzes the input file and automatically calculates possible bitrate range and or average bitrate In the last pass the encoder distributes the available bits among the entire video to achieve uniform quality 10 See also editBitrate Average bitrate Constant bitrate Adaptive bitrate streamingReferences edit Variable Bitrate knowledgebase Hydrogenaudio 2007 archived from the original on 2014 07 06 retrieved 2009 09 30 a b c VBR Glossary AfterDawn archived from the original on 2010 01 28 retrieved 2009 09 30 Variable bit rate wiki Audacity archived from the original on 2009 09 08 retrieved 2009 09 30 LAME VBR variable bitrate settings knowledgebase Hydrogenaudio 2009 archived from the original on 2014 06 06 retrieved 2009 09 30 Multi pass encoding Glossary AfterDawn archived from the original on 2009 09 18 retrieved 2009 09 30 Multi pass Encoding Wiki Digital Digest 2007 archived from the original on 2009 10 01 retrieved 2009 09 30 Multipass encoding Ripping Glossary Doom 9 2004 04 20 archived from the original on 2009 02 20 retrieved 2009 09 30 Rate Control Encoding Mode H 264 AVC options explained wiki documentation Avidemux 2009 archived from the original on 2009 07 29 retrieved 2009 09 30 Encoding with the x264 codec Encoding with MEncoder HU MPlayer team archived from the original on 2010 03 01 retrieved 2009 10 01 DVDGuy 2006 06 21 Xvid Setup Guide Digital Digest archived from the original on 2010 03 04 retrieved 2009 10 01 DivX 4 x Codec Setup Guide Digital Digest 2001 08 27 archived from the original on 2010 03 22 retrieved 2009 10 04 TMPGEnc Explained V2 0 1 Video help 2001 08 27 archived from the original on 2011 06 07 retrieved 2009 10 04 Average Bitrate knowledgebase Hydrogenaudio 2007 archived from the original on 2014 07 06 retrieved 2009 10 01 Variable Bitrate knowledgebase Hydrogenaudio 2007 archived from the original on 2014 07 06 retrieved 2009 10 04 LAME VBR knowledgebase Hydrogenaudio 2007 archived from the original on 2014 06 06 retrieved 2009 10 04 Average Bitrate knowledgebase Hydrogenaudio 2007 archived from the original on 2014 07 06 retrieved 2009 10 01 a b Rate Control Encoding Mode H 264 AVC options explained wiki documentation Avidemux 2009 archived from the original on 2009 07 29 retrieved 2009 09 30 Retrieved from https en wikipedia org w index php title Variable bitrate amp oldid 1106833387, wikipedia, wiki, book, books, library,
