External links
- Nandub project page at Sourceforge
- Guide to SBC at Digital-Digest
- Nandub Options Explained by Koepi, Encoding in Nandub on Doom9.org
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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[ citation needed ] 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.[ citation needed ]
The DivX 3.11 Alpha codec allowed a user to control three aspects of the encoding process: the average bitrate, 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 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 VirtualDub video encoder performed by Nando that incorporated SBC features.
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A codec is a device or computer program which encodes or decodes a digital data stream or signal. Codec is a portmanteau of coder-decoder.
In signal processing, 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 reduces bits by identifying and eliminating statistical redundancy. No information is lost in lossless compression. Lossy compression reduces bits by removing unnecessary or less important information. Typically, a device that performs data compression is referred to as an encoder, and one that performs the reversal of the process (decompression) as a decoder.
A keyframe in animation and filmmaking is a drawing that defines the starting and ending points of any smooth transition. The drawings are called "frames" because their position in time is measured in frames on a strip of film. A sequence of keyframes defines which movement the viewer will see, whereas the position of the keyframes on the film, video, or animation defines the timing of the movement. Because only two or three keyframes over the span of a second do not create the illusion of movement, the remaining frames are filled with inbetweens.
In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storing, handling, and transmitting content. The different versions of the photo of the cat to the right show how higher degrees of approximation create coarser images as more details are removed. This is opposed to lossless data compression which does not degrade the data. The amount of data reduction possible using lossy compression is much higher than through lossless techniques.
MP3 is a coding format for digital audio. Originally defined as the third audio format of the MPEG-1 standard, it was retained and further extended—defining additional bit-rates and support for more audio channels—as the third audio format of the subsequent MPEG-2 standard. A third version, known as MPEG 2.5—extended to better support lower bit rates—is commonly implemented, but is not a recognized standard.
A video codec is an electronic circuit or software that compresses or decompresses digital video. It converts uncompressed video to a compressed format or vice versa. In the context of video compression, "codec" is a concatenation of "encoder" and "decoder"—a device that only compresses is typically called an encoder, and one that only decompresses is a decoder.
DivX is a brand of video codec products developed by DivX, LLC.
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 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.
Xvid is a video codec library following the MPEG-4 video coding standard, specifically MPEG-4 Part 2 Advanced Simple Profile (ASP). 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.
Windows Media Video (WMV) is a series of video codecs and their corresponding video coding formats developed by Microsoft. It is part of the Windows Media framework. WMV consists of three distinct codecs: The original video compression technology known as WMV, was originally designed for Internet streaming applications, as a competitor to RealVideo. The other compression technologies, WMV Screen and WMV Image, cater for specialized content. After standardization by the Society of Motion Picture and Television Engineers (SMPTE), WMV version 9 was adapted for physical-delivery formats such as HD DVD and Blu-ray Disc and became known as VC-1. Microsoft also developed a digital container format called Advanced Systems Format to store video encoded by Windows Media Video.
Nero Digital is a brand name applied to a suite of MPEG-4-compatible video and audio compression codecs developed by Nero AG of Germany and Ateme of France. The audio codecs are integrated into the Nero Digital Audio+ audio encoding tool for Microsoft Windows, and the audio & video codecs are integrated into Nero's Recode DVD ripping software.
Transcoding is the direct digital-to-digital conversion of one encoding to another, such as for movie data files, audio files, or character encoding. This is usually done in cases where a target device does not support the format or has limited storage capacity that mandates a reduced file size, or to convert incompatible or obsolete data to a better-supported or modern format.
x264 is a free and open-source software library and a command-line utility developed by VideoLAN for encoding video streams into the H.264/MPEG-4 AVC format. It is released under the terms of the GNU General Public License.
Global motion compensation(GMC) is a motion compensation technique used in video compression to reduce the bitrate required to encode video. It is most commonly used in MPEG-4 ASP, such as with the DivX and Xvid codecs.
Α video codec is software or a device that provides encoding and decoding for digital video, and which may or may not include the use of video compression and/or decompression. Most codecs are typically implementations of video coding formats.
Rate-distortion optimization (RDO) is a method of improving video quality in video compression. The name refers to the optimization of the amount of distortion against the amount of data required to encode the video, the rate. While it is primarily used by video encoders, rate-distortion optimization can be used to improve quality in any encoding situation where decisions have to be made that affect both file size and quality simultaneously.
High Efficiency Video Coding (HEVC), also known as H.265 and MPEG-H Part 2, is a video compression standard, designed as a successor to the widely used Advanced Video Coding. In comparison to AVC, HEVC offers from 25% to 50% better data compression at the same level of video quality, or substantially improved video quality at the same bit rate. It supports resolutions up to 8192×4320, including 8K UHD, and unlike the primarily 8-bit AVC, HEVC's higher fidelity Main10 profile has been incorporated into nearly all supporting hardware. HEVC is competing with the royalty-free AV1 coding format for standardization by the video standard working group NetVC of the Internet Engineering Task Force (IETF).
In signal processing, sub-band coding (SBC) is any form of transform coding that breaks a signal into a number of different frequency bands, typically by using a fast Fourier transform, and encodes each one independently. This decomposition is often the first step in data compression for audio and video signals.
Apple ProRes is a high quality, lossy video compression format developed by Apple Inc. for use in post-production that supports up to 8K. It is the successor of the Apple Intermediate Codec and was introduced in 2007 with Final Cut Studio 2. The ProRes family of codecs use compression algorithms based on the discrete cosine transform (DCT) technique, much like the H.26x and MPEG standards. ProRes is widely used as a final format delivery method for HD broadcast files in commercials, features, Blu-ray and streaming.
