Smart Bitrate Control
Encyclopedia
Smart Bitrate Control, commonly referred to as SBC, was a technique for achieving greatly improved video compression efficiency using the DivX
3.11 Alpha video codec
or Microsoft's proprietary MPEG4v2 video codec and the Nandub video encoder
. SBC relied on two main technologies to achieve this improved efficiency: Multipass encoding and Variable Keyframe Intervals (VKI). SBC ceased to be commonly used after XviD
and DivX development progressed to a point where they incorporated the same features that SBC pioneered and could offer even more efficient video compression without the need for a specialized application. Files created by SBC are compatible with DivX 3.11 Alpha and can be decoded by most codecs that support ISO MPEG4 video.
, keyframe interval, and whether the codec preserved smoother motion or more detailed images. DivX attempted to encode an entire movie at an average bitrate the user specified, varying the quality of the video in order to achieve the target bitrate
. This meant that a simple section of video, such as a still image, would look very good, but complex video, such as an action scene, would look very bad. DivX's keyframe placement was also very simplistic, it would place keyframes only on the interval that the user selected, every 300 frames (10 seconds at 30 frame/s) by default.
Nandub's multipass encoding encoded the video twice; in the first pass it would analyze the video (and write informations to a log file), in the second it would actually produce the output file. Instead of varying the image quality to achieve an average bitrate, this allowed SBC to vary the bitrate to achieve an average quality, using higher bitrate for more complex scenes and lower bitrate for simpler scenes. VKI would place keyframes only where needed, such as at scene changes, rather than at a fixed interval. This significantly improved both the compression efficiency and visual quality of the resulting video. A VKI patch (called the DivX Scene Detect Patch) was also available for DivX to allow for VKI functionality without using Nandub, but it offered inferior performance compared to the VKI algorithms included in Nandub.
Nandub was a modification of the Open Source
VirtualDub
video encoder performed by Nando that incorporated SBC features.
DivX
DivX is a brand name of products created by DivX, Inc. , including the DivX Codec which has become popular due to its ability to compress lengthy video segments into small sizes while maintaining relatively high visual quality.There are two DivX codecs; the regular MPEG-4 Part 2 DivX codec and the...
3.11 Alpha video codec
Video codec
A video codec is a device or software that enables video compression and/or decompression for digital video. The compression usually employs lossy data compression. Historically, video was stored as an analog signal on magnetic tape...
or Microsoft's proprietary MPEG4v2 video codec and the Nandub video encoder
Encoder
An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...
. SBC relied on two main technologies to achieve this improved efficiency: Multipass encoding and Variable Keyframe Intervals (VKI). SBC ceased to be commonly used after XviD
XviD
Xvid is a video codec library following the MPEG-4 standard, specifically MPEG-4 Part 2 Advanced Simple Profile . It uses ASP features such as b-frames, global and quarter pixel motion compensation, lumi masking, trellis quantization, and H.263, MPEG and custom quantization matrices.Xvid is a...
and DivX development progressed to a point where they incorporated the same features that SBC pioneered and could offer even more efficient video compression without the need for a specialized application. Files created by SBC are compatible with DivX 3.11 Alpha and can be decoded by most codecs that support ISO MPEG4 video.
Technical details
The DivX 3.11 Alpha codec allowed a user to control three aspects of the encoding process: the average bitrateAverage bitrate
Average bitrate refers to the average amount of data transferredper unit of time, usually measured per second. This is commonly referred to for digital music or video. An MP3 file, for example, that has an average bit rate of 128 kbit/s transfers, on average, 128,000 bits every second...
, keyframe interval, and whether the codec preserved smoother motion or more detailed images. DivX attempted to encode an entire movie at an average bitrate the user specified, varying the quality of the video in order to achieve the target bitrate
Bitrate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
. This meant that a simple section of video, such as a still image, would look very good, but complex video, such as an action scene, would look very bad. DivX's keyframe placement was also very simplistic, it would place keyframes only on the interval that the user selected, every 300 frames (10 seconds at 30 frame/s) by default.
Nandub's multipass encoding encoded the video twice; in the first pass it would analyze the video (and write informations to a log file), in the second it would actually produce the output file. Instead of varying the image quality to achieve an average bitrate, this allowed SBC to vary the bitrate to achieve an average quality, using higher bitrate for more complex scenes and lower bitrate for simpler scenes. VKI would place keyframes only where needed, such as at scene changes, rather than at a fixed interval. This significantly improved both the compression efficiency and visual quality of the resulting video. A VKI patch (called the DivX Scene Detect Patch) was also available for DivX to allow for VKI functionality without using Nandub, but it offered inferior performance compared to the VKI algorithms included in Nandub.
Nandub was a modification of the Open Source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
VirtualDub
VirtualDub
VirtualDub is a video capture and video processing utility for Microsoft Windows written by Avery Lee.It is designed to process linear video streams, including filtering and recompression...
video encoder performed by Nando that incorporated SBC features.