Glossary

16:9	The aspect ratio of the movie. Very rarely equals exactly 16 divided by 9, but differs depending on the cinematic system that the movie was intended for. Usual figures varies between 1.6 and 1.82.

3ivx	An MPEG4 based video codec by 3ivx. 3ivx encoded movies are usually stored in mp4 containers. 3ivx movies can be played in Chroma either using externally supplied 3ivx QuickTime components or using the built-in 3ivx compatible codec.

4:3	The aspect ratio of the movie. 4:3, or 1.33, is the aspect ratio of most TV systems, and movies made for TV presentation usually have 4:3 aspect ratio.

5.1	The term "5.1" refers to six channel audio, of which five are regular quality (front, left, right, back left, back right) and one lower quality omnidirectional subwoofer channel.

artifact

Artifacts in video refers to visible anomalies introduced during the encoding, decoding or transmission. Common artifacts are blockyness, green squares, weaving, banding of areas with uniform color and motion jitter.

AAC	Acronym for Advanced Audio Codec, an audio codec which is an improved version of mp3. Also see mp4.

AC-3	An advanced audio codec defined by ATSC. Sometimes referred to by the document name A/52. Notable feature is 5.1 audio support. See our codecs page for plug-in download information.

aspect ratio

The numeric quotient between with and height, in display units (e.g 40cm/30cm = 1.333 aspect). Slightly complicated by the fact that most pixels are not square, so a movie with 640 pixels wide and 480 pixels high does not necessarily have an aspect ratio 1.33.

AVI

AVI is an acronym for Audio Video Interleaved, and is a container format popularized by Microsoft's early use of it. Though quite limited, it has become very popular because of its simplicity. The codecs that compressed the video or audio in an AVI are referred to by a four character code, also known as FourCCs. Officially has no support for b-frames, but several (incompatible) workarounds exist. While nowadays often associated with DivX codecs, the format can carry anything from uncompressed video to h.264.

b-frame

Abbreviation for bidirectional frame; a frame that depends on both past and future frames. Used by most newer codecs, but requires a container format that supports out-of-order frames like MPEG or QuickTime .mov (after version 7). Also see i-frame and p-frame.

codec

Acronym for COmpressor/DECompressor, though a codec does not necessarily have both parts. Codecs exist for both video and audio, and in general you will need the same codec to decompress a movie with which the movie was compressed with. Codecs compress the video or audio to take less storage space or bandwidth by removing redundant information and removing visual or audio components of the signal that humans cannot see or hear. More advanced codecs can reduce the storage more without causing artifacts, but generally requires more processor use. Common codec examples are XviD, h.264 and Sorenson Video 3.

component

A QuickTime component is a Plug-In that will extend QuickTime with new capabilities. This is usually a codec, but can be other things too like filters and importers. The components usually have ending ".component", but can also be called ".qtx". These files are installed by putting them into either the /Library/QuickTime folder or the Library/QuickTime folder in your home folder. After installation, restart all QuickTime based applications, as well as Chroma. Note: Components only work for the architecture they were written for. If you have an Intel Mac, running an Intel (aka Universal) application, it will not see your PowerPC components. You need to upgrade those components to Universal, too. However, if you run the application using Rosetta emulation (Use 'Get Info' in finder on the application and check 'Open using Rosetta'), your Intel Mac can use 'old' PowerPC components.

container format

A file-format for storing audio and video data in. Common examples are AVI, QuickTime 'mov' files, and mp4. Some generic container formats are relatively independent of codecs, i.e. MPEG4 encoded movies can be stored in AVI, QuickTime 'mov' and mp4 files, and some container formats are only designed to carry a certain codec. No movie player can play all files with a specific container format, because they might not have the codec that compressed the movie inside the container format. The independence of container format and codecs mean that new, better codecs can be invented without requiring new file formats, but it also means that you can never be sure you'll be able to play a movie with certain container format because it might use codecs you don't have.

deinterlace

Deinterlacing is the somewhat misnamed process of converting video content originally sampled as interlaced to progressive, usually for viewing on a computer monitor, which is a progressively scanned display. Since this process cannot be performed perfectly, the deinterlaced content always contains artifacts. Several methods to do this exists, all with different trade-offs as none can be perfect. Sometimes the word is used to incorrectly refer to reverse telecine.

DivX	A video codec by DivX. It's a subset of the MPEG4 standard. Commonly stored in AVI containers. DivX has added functionality for storing b-frames in AVI. DivX files can be played in Chroma either using externally supplied DivX QuickTime components or using the built-in DivX compatible codec.

DV

DV is a video codec made especially for consumer video cameras. It is quite different from other codecs in that it is always interlaced, only supports the standard definition (SD) TV frame resolution and frame rates, uses a fixed 28Mbit/s bandwidth and only uses i-frames and uncompressed audio. This makes the codec take up a great deal of bandwidth and/or diskspace, but makes editing easier. DV encoded film is generally re-encoded with a different codec (like MPEG2) for distribution after editing is finished. Unfortunately this re-encoding can give artifacts especially if the other codec does not support interlaced video, which DV always is.

FourCC

Acronym for Four Character Code, a codec designation that consists of four characters, especially popular with AVI files. Examples of FourCCs: 'DX50' (DivX video codec), 'XVID' (XviD video codec), 'avc1' (h.264 video codec). FourCCs are usually tied to a certain container format, which means that e.g. the h.264 codec usually has FourCC 'H264' in AVI but 'avc1' in QuickTime '.mov' files. Some container formats like ogg and FLV use other different systems to refer to codecs.

FLV	Acronym for FLash Video, FLV is a stream based video container format. Currently the .flv files can either contain a specialized version of h.263 video (older format) or a specialized version of VP6 (newer format).

h.263

h.263 is a video codec of the same generation as MPEG4. It was defined by the ITU as a codec for video telephony, but can sometimes be found in generic containers. QuickTime supports h.263 and so does Chroma. Earlier versions of the video format for Adobe Flash videos (found in FLV files) was based on h.263.

h.264

Also know as JVT (Joint Video Team), AVC (Advanced Video Codec) or MPEG4 part 10, a codec successor to MPEG4. It has several names because it was a joint effort between the MPEG Group (as "MPEG4 part 10") and ITU-T (as "h.264") to define the next generation of video codec. h.264 saves around 20% on the size of MPEG4 to the price of about twice the decoding time. h.264 streams are usually found in AVI, QuickTime 'mov', mp4 or MPEG Transport Streams. An h.264 codec comes with QuickTime 7 and thus can be played in Chroma. Note that newer movies from Apple encoded in h.264 appear especially sharp; this is not due to the newer codec, but due to the encoding process where excessive image sharpening has been applied. This unfortunately looks very bad when the movie is resized.

HD	Acronym for High Definition; a loosely defined term for anything with greater resolution than broadcast TV (also known as Standard Definition, SD). Usually has a 16:9 aspect ratio to make movie transfers easy.

i-frame

Abbreviation for intra frame. Differs from p-frames and b-frames in that decoding the frame is not dependent on any other frame. All codecs use i-frames every now and again to prevent artifacts. Some codecs like DV and MJPEG uses only i-frames. This makes it very easy to edit, since the movie can be cut at any point and still play, since every frame is independent. Only having i-frames also allows playing at different rates and even backwards. i-frames are however generally several times larger than b or p-frames.

IntelliAspect

A feature of Chroma's fullscreen presentation. If the movie has only slightly different aspect ratio than the screen, Chroma will fill the screen for a more pleasant viewing. Turning off IntelliAspect reverts to the correct aspect ratio but might give black bars around the movie (aka letterboxed).

interlaced

Interlaced video is the opposite of progressive, and refers to coding first every second line starting from the top (the first field), then every line inbetween (the second field). Interlaced video was invented to be able to broadcast TV since TV picture tubes were too slow to handle progressive video, which would have caused horrible flickering. Interlaced is sometimes stated as inferior to progressive, which in fact it is not; it is merely a different way of transmitting the same video information. Interlaced video does make it very difficult for codecs to efficiently compress movies, and many codecs do not support interlaced video (notably exceptions being MPEG2 and DV). Once content has been sampled in interlaced format, it cannot be converted to progressive format due to the different scanning patterns. This unfortunately makes viewing interlaced content (made for TV, e.g. DVD) on a progressive display (e.g. a computer monitor) prone to artifacting. The process of doing this conversion anyway is called deinterlacing.

letterbox

Movies created for cinematic presentation usually have an aspect ratio of 1.6 to 1.82. This is commonly known as "16:9". Since a TV, and many computer monitors, have an aspect of 1.33 (aka "4:3"), a movie is much wider than a monitor. To fit the movie, black bars must be added above and below the movie, causing the movie to look like it's viewed through a letterbox slot. A similar problem occurs with newer 'widescreen' (16:9) monitors when viewing TV (4:3) content: black bars must be added to the left and right sides to preserve aspect ratio. They are sometimes called 'sideburns'. To prevent either of these, Chroma introduces IntelliAspect.

Matroska

Matroska is a container format like AVI or QuickTime .mov. It is a new format quite similar to QuickTime .mov, designed to be vendor and codec neutral without legacy issues. Matroska files usually carries a .mkv file extension. See our codecs page for plug-in download information.

MJPEG

Abbreviation for Motion JPEG. MJPEG is a video codec which only contains i-frames which makes it suitable for editing, but makes the video take up a lot of space. MJPEG is based on the image JPEG compression standard, but several vendors have made different and incompatible versions. Some MJPEG implementations support interlaced video.

mp3

An audio codec. Its full name is MPEG1 layer 3. mp3 is a common audio codec for AVI movies with DivX video. The mp3 data format is somewhat a hybrid of a codec and a container, which makes it possible to have stand-alone .mp3 files, as well as put into a generic container format like Matroska or QuickTime .mov. There is an mp3 codec bundled with QuickTime.

mp4

A container format, designed to carry the MPEG4 codec. Internally very similar to the QuickTime 'mov' format. QuickTime supports mp4 containers since QuickTime 6. mp4 is also sometimes confusingly used to refer to the MPEG4 AAC audio codec. The mp4 container format is also very different from the stream-based MPEG container format.

MPEG Group

Acronym for Motion Pictures Expert Group. The MPEG group has defined both two container formats (see mpeg and mp4) and several codecs (MPEG1, MPEG2, MPEG4, MPEG4-AVC/h.264).

mpeg

mpeg is a container format for several video codecs, notably MPEG1 and MPEG2, but can also carry h.264. MPEG4 is usually put into .mp4 containers. mpeg is technically a stream format for e.g. TV broadcast, but can be stored as files, usually with the extension .mpeg or .mpg. The most common codec in .mpg files is MPEG1, which Chroma can play, but sometimes it contains MPEG2, which Chroma cannot play.

MPEG1

MPEG1 was the first generation codecs defined by the MPEG Group. By todays standards it is quite primitive, but still quite widely used because nearly every player (like Chroma) can play it, and it is considered nearly patent-free. Used in VideoCDs. Does not support interlaced video.

MPEG2

MPEG2 was the second generation video codec as defined by the MPEG Group. It supports bigger frames and higher bitrates compared to MPEG1, but the most notably improvement is support for interlaced video. MPEG2 is the only codec available for DVDs, and is also used for TV broadcasts, especially newer HDTV broadcasts. Due to complicated patent licensing, MPEG2 is not very widespread. Chroma does not support MPEG2 for this reason.

MPEG4

An ISO standard for media transportation. References to MPEG4 usually means the video codec standard part of the MPEG4 standard. MPEG4 is a successor to MPEG2. (There was no MPEG3 standard to prevent confusion with mp3's). Superseded by MPEG4 part 10, aka h.264. The MPEG4 Visual is the basis of the DivX codec, the XviD codec as well as QuickTime 6's MPEG4 codec.

on2	A company formerly known as the Duck Corporation, on2 has defined several video codec formats: Duck Truemotion, Duck Truemotion2, VP3, VP4, VP5, VP6 and VP7.

ogg

ogg is a container format created by Xiph specifically to carry Theora video and Vorbis audio. Therefore it is not a general container format like Matroska or QuickTime .mov. Usually carries an .ogg file extension. As Theora is relatively new, many .ogg files only carry Vorbis audio, much like .mp3 files. See our codecs page for plug-in download information.

p-frame

Abbreviation for predicted frame. Used in video codecs to minimize the storage requirement by only storing the difference since last frame. Used in almost all video codecs, but always together with a few i-frames to minimize artifacts. Also see i-frame and b-frame.

pixel

Abbreviation for PIcture ELement. Analog video (e.g TV) does not have discrete picture elements, but most computer graphics systems divide the picture into rows and columns of pixels. In video terminology, pixels are sometimes called pels (also from Picture ELements).

progressive

Progressive video content is the opposite of interlaced, and refers to coding the video line by line starting from the top. This is the way computer monitors display video. Viewing interlaced video (from e.g. a DVD) on a progressive video display (like a computer monitor) gives artifacts; the picture looks sheared or combed. It is unfortunately not possible to transform interlaced sampled content to progressive without image degradation. Fortunately many newer DVDs, especially with content originating from movies, are "progressive" (first field and second field are sampled from the same frame, and all lines sampled at the same time) and makes viewing on a computer possible. Otherwise a deinterlace step is needed.

QuickTime

When people refer to 'QuickTime', they generally mean either The QuickTime library for handling media, The native container format for said library (.mov), The "QuickTime codec" which is really SVQ3, or The reference media player, QuickTime Player. Unless we specify, we always mean the library.

SVQ3

Acronym for Sorenson Vector Quantizer 3. SVQ3 is an advanced proprietary codec format that is only found in QuickTime movies due to a licensing agreement between Sorenson and Apple. The SVQ3 format is loosely based on an early draft of the h.264 standard, and is actually not a vector quantizer codec. The SVQ3 codec is therefore somewhere between MPEG4 and h.264 in efficiency and decoding requirement. The QuickTime 'mov' format has to the general public become equivalent with the Sorenson SVQ3 codec. The SVQ3 codec is bundled with QuickTime and SVQ3 movies can be played in Chroma.

telecine

Telecine is the process of converting movie format (cinematography) to video (television). This is needed to transfer e.g. movie films to DVDs. The complicating factor is that movie films runs at 24 frames per second, while TV frames run at 50 fields (25 frames) per second (PAL) or 60 fields (30 frames) per second (NTSC), which means a fairly convoluted frame-to-field conversion process (e.g. '2-3 pull-down'). The reverse process, going from TV (DVD) content to 24 frames per second progressive display, is called reverse telecine. (Sometimes people refer to reverse telecine incorrectly as "telecine"). The telecine process is generally reversible without any artifacting ('3-2 pull-up'), but sometimes the original telecine conversion was done with a video camera, which is cheaper but no longer reversible since the video is now irreversibly interlaced.

Theora

Theora is a video codec made by Xiph. It is based off the released source code of VP3, and as such it is of the same codec generation as MPEG4. Theora is very rarely found in anything but the ogg container format. See our codecs page for plug-in download information.

VC-1

Acronym for Visual Codec #1. It is an advanced video codec on par with or better than h.264. It used to be called VC-9 and some references to VC-9 still exists. The codec was invented by Microsoft (as WMV3) and donated to the SMPTE standards committee. VC-1 and WMV3 are not binary compatible but very similar.

Vorbis

Vorbis is an audio codec, generally regarded to be slightly better than mp3. It was created by Xiph and they have a QuickTime codec available. Usually carried in an ogg container. See our codecs page for download information.

VP3	A video codec of the same generation as MPEG4, created by the on2 company. on2 later released the source code for VP3, and it became the basis for the Theora codec. See our codecs page for download information.

VP6	A video codec created by the on2 company. While available as a stand-alone codec for PC (but has not been made available as a QuickTime codec), it is mostly used in newer Adobe Flash movies.

WMV	Acronym for Windows Media Video. It is a container format (usually with a .wmv file extension) for codecs like WMV1, WMV2, WMV3 or VC-1. See our codecs page for plug-in download information.

WMV3	Acronym for Windows Media Video codec #3. Part of the "Windows Media 9" architecture. It is quite different from earlier WMV1 and WMV2 (which are MPEG4 based) and is on par with or better than h.264. The VC-1 codec is based on WMV3. See our codecs page for plug-in download information.

XviD	MPEG4 based video codec by XviD. Commonly stored in AVI containers. XviD movies can be played in Chroma either using externally supplied XviD QuickTime components or using the built-in XviD compatible codec.

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