Smart Bitrate Control (SBC) was a technique for achieving greatly improved
video 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 ...
efficiency using the
DivX
DIVX (Digital Video Express) is a discontinued digital video format. Created in part by Circuit City, it was an unsuccessful attempt to create an alternative to video rental in the United States. The format's poor reception from consumers resu ...
3.11 Alpha
video codec
A video codec is software or Computer hardware, hardware that data compression, compresses and Uncompressed video, decompresses digital video. In the context of video compression, ''codec'' is a portmanteau of ''encoder'' and ''decoder'', while ...
or Microsoft's proprietary
MPEG-4v2 video codec and the
Nandub video encoder. SBC relied on two main technologies to achieve this improved efficiency:
multi-pass 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
International Organization for Standardization
The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries.
M ...
(ISO) MPEG4 video.
Technical details
The DivX 3.11 Alpha codec allowed a user to control three aspects of the encoding process: the
average bitrate
In telecommunications, average bitrate (ABR) refers to the average amount of data transferred per unit of time, usually measured per second, commonly for digital music or Digital video, video. An MP3 file, for example, that has an average bit rate ...
,
keyframe
In animation and filmmaking, a key frame (or keyframe) is a drawing or shot that defines the starting and ending points of a smooth transition. These are called ''frames'' because their position in time is measured in frames on a strip of film ...
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
In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time.
The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...
. 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 information 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 is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...
VirtualDub
VirtualDub is a free and open-source 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. It uses AVI container format to s ...
video encoder performed by Nando that incorporated SBC features.
See also
*
Variable bitrate
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 ...
External links
Nandub project page at Sourceforge
{{Compression Methods
Data compression
Video codecs