DivX codec - compressor / decompressor
DivX MPEG-4 Description
DivX is based on the MPEG-4 compression format. MPEG-4 is a new standard of video compression that is both high quality and low bitrate. They are usually only a fraction (around 15%) of the size of a standard DVD, even at 640x480 resolutions, making them the best home video format thus far. They only take half the time to encode, and yet at the same time is smaller in size than MPEG-1 - due to their incredible compression technology - some have even called MPEG-4 the "MP3 of the video world". Quality ranges from net-streaming quality to DVD and better!. Currently, DivX is playable on computers only, not on DVD players or MPEG cards.
MPEG-4 video compression standard, designed primarily for video transfer over low to mid bandwidth networks (eg. Internet, WAP ...). There are in fact 2 major codecs, both name the "DivX codec". But the newer one, which used to be part of the open-sourced project at Project Mayo (now under a licensing scheme), is more commongly referred to as "DivX For Windows/Linux/Mac ...", whereas the orginal codec is sometimes referred to as the "DivX ;-) Codec". The version number of these 2 major codecs are also different - the original being 3.xx, while the new ProjectMayo codec has a version number of 4.xx. Most older/existing movies are encoded with "DivX ;-) Codec", since the new ProjectMayo DivX codec is still being developed. The original DivX 3.xx codec is based on Microsoft's MPEG-4 V3 codec (ASF was based on MPEG-4 V2). The reason why the codec was "hacked" and re-distributed is because Microsoft's codec did not allow one to encode to AVI (they only wanted people to encode to ASF/WMV), which is far from being convenient. The DivX 3.xx codec also includes hacked versions of a MP3 codec and a WMA codec. The AnglePotion, MPEG-4 and SMR codecs are all in the same boat. There is also a VKI (Scene Detect) patch that will insert keyframes at scene changes for you automatically, which will improve picture quality. The new DivX 4.x codec has nothing to do with Microsoft - it has been developed entirely from scratch, and is still under development (hence less then perfect compatibility/efficiency/quality). In time, the DivX 4.xx codec will completely replace the 3.xx codec, but for now, the 3.xx codec offers better compatibility/efficiency/quality. The 4.xx codec is not compatible with the 3.xx codec, and vice versa.
DivX Download
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DivX 5.1.1 Features
Support for interlaced video in the decoder. Preserving the interlaced fields of interlaced video may sometimes result in better video quality during playback.
New de-ringing post-processing algorithm. The new algorithm improves the perceived video quality during playback. It is activated when the post-processing level is set to Level 6.
Video Buffer Verifier (VBV) model (one and two pass encoding). The VBV ensures that the maximum peak bit rate never exceeds either the user's inputted "maximum peak" bit rate value or/and ensures that the encoded stream never violates the buffer of an MPEG-4 compliant decoder. This helps to prevent decoding failure in both hardware and software where memory may be limited yet compliant! to the MPEG-4 standard as defined in ISO/IEC 14496-2:2001(E). In order for DivX video to be successfully delivered over a restricted channel in real time to a decoder, the encoder's rate control must ensure that the decoder's buffer is not violated. When this is done properly, then overflow and underflow will never occur and the encoder is said to be "VBV compliant." It makes no difference whether the video is encoded in 1-pass or many, in real-time or offline. It is the encoder's rate control that must ensure compliance. There are three main requirements of a VBV-compliant rate control algorithm, in order of importance:
VBV compliance. When VBV parameters are specified (size, initial occupancy, channel characteristics) the rate control should avoid producing video that is in danger of violating the decoder's buffer. Bitstream stuffing may be used in extreme cases to prevent overflow in true CBR systems. Underflow must be prevented by increasing frame quantiser or by! dropping frames.
Target bitrate. We aim to meet the user's requirements as accurately as possible here. This is directly related to filesize.
Good-looking video. Rate control should aim to produce the subjectively best quality video given other constraints. Consistency is important here as changes in quality are very noticeable and video is often judged by the worse quality segment in the whole sequence.
Nth Pass? encoding. Another new addition to the rate control arsenal, Nth Pass? encoding takes advantage of information available from previous analysis (or analyses) of the video sequence. Nth Pass encoding uses information garnered from previous passes through the video sequence, which can improve quality with each pass. There are four main steps to Nth Pass encoding:
Analysis (the first pass)
Map generation (where the results of analyses are processed)
Strategy generation (strategist examines map of the video seque! nce and creates a strategy that will best achieve the three VBV RC requirements)
In-loop nth pass rate control (uses information from the map and strategy to effect rate control that best fulfills the three requirements)
Support for DivX Certified Profiles. With the new DivX Certification program, DivXNetworks is enabling third parties to create "DivX Certified" products that are rigorously tested and fully compatible with the entire suite of DivX- video technologies. There are four levels of official DivX Certified video products: Handheld Video Devices, Portable Video Devices, Home Theater Video Devices and High Definition Video Devices. These levels quickly and clearly communicate what type and size of DivX video are supported on the certified device. Now, when you encode video, you have the option to force your video to comply with one of the DivX Certified Profiles to ensure that your video will play back properly on certified products.DivX Decoder verification logo. There is a new semi-transparent DivX Logo that will appear by default for a few seconds any time you use the DivX decoder to watch a DivX video. This instantly lets you know you're watching a true DivX- video. You can turn the display of the logo on or off in the codec properties dialog.
New internal application programming interface (API). The internal API of the codec was changed to better accommodate integration with third party partners. This only affects you if you are a DivX licensee and are working directly with the DivX object code. The external API (e.g., DirectShow, etc.) remains unchanged.
Improved:
The motion estimation algorithm is better optimized for High Definition resolutions (up to 1080p, or 1920 x 1080 pixel resolution
The pre-processing performance is now improved with with the IYUY 4:2:0 color space
Changed:
Removed MP4creator and t! he MPEG-4 file output option due to some compliance issues. This will return in our next release once these issues are resolved.
Removed the Intelligent IVTC functionality due to persistent problems caused by lack of variable frame rate file format support. This technology will be back soon in a new form...
Changed the block skipping threshold for high quantizers, which improves visual quality when high quantizers are used.
Fixed:
Fixed a bunch of little cosmetic bugs in the DirectShow decoder properties page.
Fixed a bug where the last P frame before an I frame was not displayed when Smooth Playback was selected.
Fixed a practically unnoticeable YUV->RGB16 color conversion rounding bug.
Fixed a bug that was the cause of some of VirtualDub's "Cannot Start Video Compression" errors.
Fixed a few issues with DivX 3.11 compatibility.
Modified the decoder to deal with a bug in the old ! OpenDivX encoder that set the scalability bit incorrectly in certain cases. The DivX decoder can now detect this problem and play the content properly.
Fixed a problem where some rounding operations were not done toward zero, as is required by section 7.4 of the spec. This fixed an intra case in MPEG-2 inverse quantization.
Fixed a bug where some frames would be corrupted by an out-of-range error.
Fixed several rounding issues related to MMX/SSE/SSE2 optimizations.
Fixed an MMX bug in RGB32 color conversion.
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