Movie Formats

Movie Formats

DivX/XviD

DivX

DivX is a brand name of products created by DivX, Inc. (formerly DivXNetworks, 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. The DivX codec uses lossy MPEG-4 Part 2 compression, also known as MPEG-4 ASP, where quality is balanced against file size for utility. It is one of several codecs commonly associated with ripping, where audio and video multimedia are transferred to a hard disk and transcoded. As a result, DivX has been a center of controversy because of its use in the replication and distribution of copyrighted DVDs. Many newer “DivX Certified” DVD players are able to play DivX encoded movies, although the Qpel and GMC features are often omitted to reduce processing requirements. They are also excluded from the base DivX encoding profiles for compatibility reasons.

XviD

Xvid (formerly “XviD”) is a video codec library following the MPEG-4 standard. Xvid features MPEG-4 Advanced Simple Profile 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 primary competitor of DivX (Xvid being DivX spelled backwards). While DivX is proprietary software, Xvid is free and open source software and, unlike DivX, can be used on many different platforms and operating systems.

x264

x264 is a free software library for encoding H.264/MPEG-4 AVC video streams. The code is written from scratch by Loren Merritt, Laurent Aimar, Eric Petit, Min Chen, Justin Clay, Måns Rullgård, Radek Czyz, Alex Izvorski, Alex Wright, and Christian Heine. It is released under the terms of the GNU General Public License.

Several graphical user interfaces have been made for the command line version, including MeGUI, AutoAC and a .NET (1.1) based x264CLI GUI.

Capabilities

As of March 2007, it is one of the most advanced publicly available AVC encoders. It is also one of the few publicly available High Profile AVC encoders. It supports:

* Context-based Adaptive Binary Arithmetic Coding (CABAC) and Context-based Adaptive Variable Length Coding (CAVLC)
* Multiple reference frames
* All intra-predicted macroblock types (16×16, 8×8 and 4×4 — 8×8 is part of AVC High Profile)
* All P-frame inter-predicted macroblock types
* B-Inter-predicted macroblock types from 16×16 down to 8×8
* Rate Distortion Optimization
* Multiple ratecontrol modes: constant quantizer, constant quality, single or multipass ABR with the option of VBV
* Scene cut detection
* Adaptive B-frame placement, with the option of keeping B-frames as references / arbitrary frame order
* 8×8 and 4×4 adaptive spatial transform (High Profile)
* Lossless mode (High 4:4:4 Profile)
* Custom quantization matrices (High Profile)
* Parallel encoding on multiple CPUs
* Interlace support
* Adaptive quantization, a newer feature which allows different quantization matrices to be used for different parts of a frame. In x264, it is used to allow the allocation of extra bits to dark background areas to avoid blocking.

DVD

DVD (also known as “Digital Versatile Disc” or “Digital Video Disc”) is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. DVDs resemble Compact Discs because their diameter is the same (120 mm or 4.72 inches, or occasionally 80 mm or 3.15 inches), but they are encoded in a different format and at a much higher density.

All read-only DVD discs, regardless of type, are DVD-ROM discs. This includes replicated (factory pressed), recorded (burned), video, audio, and data DVDs. A DVD with properly formatted and structured video content is a DVD-Video disc. DVDs with properly formatted and structured audio are DVD-Audio discs. Everything else (including other types of DVD discs with video) is referred to as a DVD-Data disc. Many people use the term “DVD-ROM” to refer to pressed data discs only, but that is not technically correct.

DVD Video

DVD-Video is a standard for storing video content on DVD media. As of 2003, DVD-Video has become the dominant form of consumer video formats in the United States, Europe, and Australia.[8]

Though many resolutions and formats are supported, most consumer DVD-Video disks use either 4:3 or 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL). Audio is commonly stored using the Dolby Digital (AC-3) and/or Digital Theater System (DTS) formats, ranging from monaural to 5.1 channel “Surround Sound” presentations. DVD-Video also supports features like selectable subtitles, multiple camera angles and multiple audio tracks.

DVD-Audio

DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channel configuration options (from mono to 5.1 surround sound) at various sampling frequencies and sample rates. Compared with the CD format, the much higher capacity DVD format enables the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction).

Despite DVD-Audio’s superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment.

Security

DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media (CPPM) developed by the 4C group (IBM, Intel, Matsushita, and Toshiba).

To date, CPPM has not been “broken” in the sense that DVD-Video’s CSS has been broken, but ways to circumvent it have been developed.[9] By modifying commercial DVD(-Audio) playback software to write the decrypted and decoded audio streams to the hard disk, users can, essentially, extract content from DVD-Audio discs much in the same way they can from DVD-Video discs.

VCD

Video CD (aka VCD, View CD, Compact Disc digital video) is a standard digital format for storing video on a Compact Disc. VCDs are playable in dedicated VCD players, nearly all personal computers, most modern DVD-Video players, and some video game consoles.

The VCD standard was created in 1993 by Sony, Philips, Matsushita, and JVC and is referred to as the White Book standard.

Video CDs are authored (or “burned”) using the Mode 2/XA format, allowing roughly 800 megabytes of VCD data to be stored on one 80 minute CD. (Versus 700 megabytes when using Mode 1) This, combined with the net bitrate of VCD video and audio, means that almost exactly 80 minutes of VCD content can be stored on an 80 minute CD, 74 minutes of VCD content to a 74 minute CD, and so on. This was done in part to ensure compatibility with existing CD drive technology, specifically the earliest “1x speed” CD drives.

Technical specifications

Video

* Codec: MPEG-1
* Resolution:
o NTSC: 352×240
o PAL/SECAM: 352×288
* Aspect Ratio:
o NTSC: 107:80 (0.3% difference from 4:3)
o PAL/SECAM: 4:3
* Framerate:
o NTSC: 29.97 or 23.976 frames per second
o PAL/SECAM: 25 frames per second
* Bitrate: 1,150 kilobits per second
o Rate Control: constant bitrate

Overall picture quality is intended to be comparable to VHS video, though visual artifacts may be noticeable in some cases. Poorly compressed video in VCD tends to be of lower quality than VHS video, but exhibiting block artifacts rather than analog noise.

352 horizontal pixels was chosen because it approximates the resolution of an analog broadcast video signal, assuming a 5 MHz bandwidth. Any more than this would be wasted in the RF modulator, which was the usual means of video input for domestic television receivers at the time.

VCD video is mostly compatible with the DVD-Video standard, except for any video encoded at 23.976 frames per second. DVD-Video requires all MPEG-1 video to be encoded at either 25 or 29.97 frames per second.

Audio

* Codec: MPEG-1 Audio Layer II
* Frequency: 44,100 hertz (44.1 kHz)
* Output: Dual channel or stereo
* Bitrate: 224 kilobits per second
o Rate Control: Constant bitrate

As with most CD-based video formats, VCD audio is incompatible with the DVD-Video standard due to the difference in frequency; DVDs require 48 kHz, whereas VCDs use 44.1 kHz.

SVCD

Super Video CD (Super Video Compact Disc or SVCD) is a format used for storing video on standard compact discs. SVCD falls between Video CD and DVD in terms of technical capability and picture quality.

Technical specifications

SVCD has two-thirds the resolution of DVD, and over 2.7 times the resolution of VCD. One CD-R disc can hold up to 60 minutes of SVCD-format video at a picture quality roughly comparable to Laserdisc. While no specific limit on SVCD video length is mandated by the specification, one must lower the video bitrate, and therefore quality, in order to accommodate very long videos. It is usually difficult to fit much more than 100 minutes of video onto one SVCD without incurring significant quality loss, and many hardware players are unable to play video with an instantaneous bitrate lower than 300 to 600 kilobits per second.

Video

* Codec: MPEG-2
* Resolution:
o NTSC: 480×480
o PAL/SECAM: 480×576
* Aspect Ratio: 4:3
* Framerate:
o NTSC: 29.97 or 23.976 frames per second
o PAL/SECAM: 25 frames per second
* Bitrate: Up to 2.6 Megabits (2,600 kilobits) per second
o Rate Control: Constant or variable bitrate

Interlaced video is supported (though not required) for SVCD video, excepting any video at 23.976 frames per second, as it must use 3:2 pulldown.

Unlike other CD-based video formats such as China Video Disc and Video CD, Super Video CD video is incompatible with the DVD-Video standard due to a conflict in resolution. However, the 480×480/576 resolution is supported by the HD DVD standard.

Audio

* Codec: MPEG-1 Audio Layer II
* Frequency: 44,100 hertz (44.1 kHz)
* Output: Monaural, dual channel, or stereo
* Bitrate: Certain bitrates between 32 and 384 kilobits per second, inclusive
o Rate Control: Constant bitrate

As with most Compact Disc-based video formats, SVCD audio is incompatible with the DVD-Video standard due to the difference in frequency; DVDs require 48 kHz, whereas SVCDs use 44.1 kHz.

Additional features

The SVCD standard supports several other features, including menus, hyperlinks, karaoke lyric highlighting, overlay subtitles, and DVD-quality slide shows with resolution up to 704×480 (NTSC) or 704×576 (PAL). SVCDs may have two separate stereo audio tracks (for commentary or additional languages); audio may have up to 8 channels (in a 7.1 arrangement) using the MPEG Multichannel surround sound format, though space constraints and poor hardware support make it somewhat impractical.

Playback issues

Presentation of SVCD titles on most players is marred by an unfortunate violation of sampling theory almost built into the spec. The “2/3″ choice for resolution is rarely consistently implemented end to end through the full player electronics. Because a DVD player might include provisions for various VCD, SVCD, and DVD horizontal resolutions (360, 480, 540 or 720) and only one analog low pass filter is provided, 2 out of the 3 formats will suffer aliasing when presented on the screen. Usually, the best resolution, DVD 720 dictates filter design, with SVCD display suffering from “foldover”. While displays should follow correct theory, the objectionable aliasing artifacts that result are usually buried in noise from other sources, such as camera, quantization, and MPEG artifacts.

XVCD/XSVCD

Designed to squeeze the most out of a CD is the DVCD or Double VCD where a non-standard CD is overburned to include up to 100 minutes of video. This format is seen only in China (although such titles can be found outside China, but they’re extremely rare), and the DVCDs are playable on many DVD or VCD players though some CD-ROM drives and players have problems reading these CDs mostly because the groove spacing is outside specifications and the laser servo is unable to track it.

XVCD

XVCD stands for eXtended VCD. It uses a much higher bit rate (3.5 Mbits per second), so it is higher quality, but can’t store as much on one CD. (Approximately one half hour.) It is not an officially recognized format, so it is harder to find DVD players that are compatible with XVCDs.

(x)VCD

There are many non standard variants of the standard Video CD. Those called (x)VCD and they supported by most (but not all) standalone DVD players.

Popular (x)VCD are KVCD (nothing more than a template for the ubiquitous TMPGenc MPEG 1/2 encoder), CVCD (a Spanish xVCD), S(x)VCD (a VCD but with vbr mpeg 2) and miniDVD. There is also SKVCD (or KSVCD) which does much the same thing as KVCD, but uses MPEG2 and adds some luxuries such as multiple audio streams and chapters. Some later flexible standalone players now support (K)SVCD, as the format has been endorsed by Philips, the custodian of all the CD standards.

Most commonly the players can have trouble with (x)VCDs.

SXVCD

Super eXtended VCDs are another hack of VCDs. They have the same bitrate as DVD (9.8 Mbits per second) and are read by most DVD players. The only major disadvantage is that very little video can be stored on an SXVCD.

CVD

The China Video Disc (or CVD) standard is a CD-based MPEG-2 audio and video format developed in 1997. It is almost identical to the SVCD standard, the only technical difference being a lower video resolution.

Technical specifications

On a technical basis the CVD standard is all but identical to the SVCD standard. The only difference between the two formats is the video resolution: SVCDs require 480×576 (PAL/SECAM) or 480×480 (NTSC) resolution video, whereas CVDs use 352×576 (PAL/SECAM) or 352×480 (NTSC) resolution video. All other technical aspects of the CVD standard are identical to those of the SVCD standard.

Video

* Codec: MPEG-2
* Resolution:
o NTSC: 352×480
o PAL/SECAM: 352×576
* Aspect Ratio: 4:3
* Framerate:
o NTSC: 29.97 or 23.976 frames per second
o PAL/SECAM: 25 frames per second
* Bitrate: Up to 2.6 Megabits (2,600 kilobits) per second
o Rate Control: Constant or variable bitrate

Interlaced video is supported (though not required) for CVD video, excepting any video at 23.976 frames per second, as it must use 3:2 pulldown.

The CVD video standard is almost completely compatible with the DVD-Video standard. However, the CVD standard does not specify any limits on GOP structure, and as such it is possible to encode CVD video with a GOP size larger than DVD-Video’s 64 frame-per-GOP limit. In practice this is highly uncommon; most commercially produced CVD video uses a 12 or 15 frame GOP structure, which is compatible with the DVD-Video standard.

Audio

* Codec: MPEG-1 Audio Layer II
* Frequency: 44,100 hertz (44.1 kHz)
* Output: monaural, dual channel, or stereo
* Bitrate: Certain bitrates between 32 and 384 kilobits per second, inclusive
o Rate Control: Constant bitrate

As with most CD-based video formats, CVD audio is incompatible with the DVD-Video standard due to the difference in frequency; DVDs require 48 kHz, whereas CVDs use 44.1 kHz.

Additional features

Support for features such as karaoke, selectable subtitles, two selectable audio tracks, and DVD-quality slide shows.

Advantages/disadvantages to SVCD

Though the lower resolution of the CVD standard brings with it less detailed video than the SVCD standard, it also provides certain advantages. Most obvious are the space requirements for “decent quality” video, as the lower resolution allows the bitrate to be reduced significantly more while keeping the number of “compression errors”, such as MPEG block artifacts, to a minimal level. Other advantages primarily center around the DVD support for the resolution; while CVD standard video is also DVD-compatible, SVCD standard video is not. Initially this is only useful for transferring CVD content to DVD, as the video does not have to be transcoded and can avoid the quality loss which would result. (Though the audio must be transcoded, as DVDs require 48 kHz audio rather than the 44.1 kHz audio used on CVDs) Additionally, CVDs do not suffer from certain playback issues faced by SVCDs due to limitations present in many DVD players. These issues are mostly due to “foldover” or aliasing problems encountered when the DVD player resizes the video as it plays it. While SVCDs are frequently affected by this issue CVDs are not, as the resizing algorithms used by DVD players are almost always optimized with valid DVD resolutions (such as the CVD resolution) in mind.

The major disadvantages of the CVD standard, aside from the lower resolution, are primarily compatibility issues. While almost all PAL DVD players which are listed as “SVCD compatible” must also support the CVD standard, DVD players sold in the United States have no such requirement. Though no solid figures exist, it has been estimated that roughly a quarter of those DVD players sold in the United States which are “SVCD compatible” do not support the CVD standard.