Editing QuickTime Animation

{{Short description|Video codec by Apple Inc}}
{{notability|date=September 2011}}
'''QuickTime Animation''' format (also known as '''QuickTime RLE''') is a [[video compression format]] and [[video codec|codec]] created by [[Apple Computer]] to enable playback of [[RGB]] video in [[Real-time computing|real time]] without expensive hardware.<ref>{{cite web|url=https://developer.apple.com/techpubs/quicktime/qtdevdocs/PDF/QTFileFormat.pdf |title=QuickTime File Format |work=Inside QuickTime: The QuickTime Technical Reference Library |publisher=Apple Inc. |format=PDF |year=2000 |access-date=5 April 2013 |url-status=dead |archive-url=https://web.archive.org/web/20000307235449/http://developer.apple.com/techpubs/quicktime/qtdevdocs/PDF/QTFileFormat.pdf |archive-date=March 7, 2000 }}</ref><ref name=wikicx>{{cite web |url=http://wiki.multimedia.cx/index.php?title=Apple_QuickTime_RLE |title=Apple QuickTime RLE |work=MultimediaWiki |date=24 May 2011 |access-date=9 April 2013}}</ref> It is generally found in the [[QuickTime File Format|QuickTime]] [[Container format (digital)|container]] with the [[FourCC]] 'rle '.<ref group="note">Three letters followed by a space.</ref> It can perform either [[lossless compression|lossless]] or [[lossy compression|lossy]] compression and is one of the few video codecs that supports an [[alpha channel]]. Supported [[color depth]]s are 1-bit (monochrome), 15-bit RGB, 24-bit RGB, 32-bit [[RGBA color space|ARGB]], as well as [[Palette (computing)|palettized]] RGB. As a result of reverse-engineering of the format, a decoder is implemented in [[XAnim]] as well as an encoder and decoder in [[libavcodec]].<ref name=xanim>{{cite web |url=http://www.math.unl.edu/~rdieter1/OpenStep/X11/xanim.2.70.6.4.2.README |title=xanim.2.70.6.4.2 README |author=Mark Podlipec |date=10 December 1997 |work=XAnim |access-date=4 April 2013 |archive-date=28 December 2015 |archive-url=https://web.archive.org/web/20151228114941/http://www.math.unl.edu/~rdieter1/OpenStep/X11/xanim.2.70.6.4.2.README |url-status=dead }}</ref><ref>{{cite web |url=http://ffmpeg.org/general.html |title=FFmpeg Documentation |author=<!--Staff writer(s); no by-line.--> |work=FFmpeg |access-date=4 April 2013}}</ref>

== Technical Details ==
QuickTime Animation uses [[run-length encoding]] and [[conditional replenishment]] for compression.<ref name=wikicx/> When encoding, the input frame is scanned pixel-wise in raster-scan order and processed line-wise.<ref name=wikicx/> Within a line, pixels are segmented into runs, the length of which is variable and signaled in the bitstream. For each run, one of three coding modes is used: same color, skip, or PCM.<ref name=wikicx/> In same color mode, a run of pixels is represented by a single color in a run-length encoding fashion. If pixels with different colors are joined into a run (of a single color) by the encoder, the coding process is lossy, otherwise it is lossless. The lossless mode is used at the 100% quality level. In skip mode, the run of pixels is left unchanged from the previous frame (conditional replenishment). In [[PCM]] mode, the color of each pixel is written to the bitstream, without any compression.<ref name=wikicx/>

Run-length encoding works well on content with large areas of constant color. Conditional replenishment works well if only small areas change from frame to frame. QuickTime Animation works well on content with both these properties, such as traditional 2-D animation and screencast content.<ref>{{cite web |url=http://boredzo.org/codec-comparison/codecs/animation.html |title=Screencast codec showdown: The codecs: Animation |author=Peter Hosey |date=8 December 2013 |access-date=9 April 2013 |archive-url=https://archive.today/20130703211054/http://boredzo.org/codec-comparison/codecs/animation.html |archive-date=3 July 2013 |url-status=dead }}</ref> For natural video and complex 3D rendered scenes, in which runs of constant color rarely occur, only low compression ratios can be achieved in lossless mode, and the merging of runs becomes visible as noise in lossy mode.

== See also ==
* [[List of codecs#Lossless video compression|List of lossless video codecs]]

== Notes ==
{{Reflist|group=note}}

== References ==
{{Reflist}}

== External links ==
* [http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/qtrle.c;hb=HEAD QuickTime Animation (RLE) Video Decoder - FFmpeg] 
* [http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavcodec/qtrleenc.c;hb=HEAD Quicktime Animation (RLE) Video Encoder - FFmpeg]

{{Compression formats}}

[[Category:QuickTime|Animation]]
[[Category:Video codecs]]

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