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{{Short description|Form of video processing}}
{{Use mdy dates|date=January 2015}}
[[File:Interframe motion interpolation.webm|thumb|right|Comparison of a slow down video without interframe interpolation (left) and with motion interpolation (right)]]
'''Motion interpolation''', '''motion-compensated frame interpolation''' ('''MCFI'''), or '''frame generation''', is a form of [[video processing]] in which intermediate film, video or animation frames are synthesized between existing ones by means of [[interpolation]], in an attempt to make animation more fluid, to compensate for [[display motion blur]], and for fake [[slow motion]] effects.
==Hardware applications==
===Devices===
Motion interpolation is a common, optional feature of various modern video devices such as [[HDTV]]s and [[AV receiver]]s, aimed at increasing perceived framerate or alleviating [[display motion blur]], a common problem on [[LCD]] [[flat-panel display]]s.
===Difference from display framerate===
A display's output [[refresh rate]], input drive signal [[framerate]], and original content framerate, are not always equivalent. In other words, a display capable of or operating at a high framerate does not necessarily mean that it can or must perform motion interpolation. For example, a TV running at 120 Hz and displaying 24 FPS content will simply display each content frame for five of the 120 display frames per second. This has no effect on the picture compared to 60 Hz other than eliminating the need for [[3:2 pulldown]] and thus film [[judder]] as a matter of course (since 120 is evenly divisible by 24). Eliminating judder results in motion that is less "jumpy" and which matches that of a [[movie projector|theater projector]]. Motion interpolation can be used to eliminate judder, but it is only necessary when targeting a framerate not evenly divisible.<ref name="Six things">{{cite web |url=http://reviews.cnet.com/4520-6449_7-6792632-1.html |title=Six things you need to know about 120 Hz LCD TVs |accessdate=2008-02-02 |last=Carnoy |first=David |date=October 25, 2007 |publisher=CNET.com}}</ref>
===Relationship to advertised display framerate===
The advertised framerate of a specific display may refer to either the maximum number of content frames which may be displayed per second, or the number of times the display is [[refresh rate|refreshed]] in some way, irrespective of content. In the latter case, the actual presence or strength of any motion interpolation option may vary. In addition, the ability of a display to show content at a specific framerate does not mean that display is capable of accepting content running at that rate; TVs above 60 Hz do not accept a higher frequency [[list of video connectors|signal]] from most or any sources, but rather use the extra refresh capability to eliminate judder, reduce [[ghosting (television)|ghosting]], display [[stereoscopy]], or create interpolated frames.
As an example, a TV may be advertised as "240 Hz", which would mean one of two things:
# The TV can natively display 240 frames per second, and perform advanced motion interpolation which inserts between 2 and 8 new frames between existing ones (for content running at 60 FPS to 24 FPS, respectively). For [[Active shutter 3D system|active 3D]], this framerate would be halved.
# The TV is natively only capable of displaying 120 frames per second, and basic motion interpolation which inserts between 1 and 4 new frames between existing ones. Typically the only difference from a "120 Hz" TV in this case is the addition of a [[strobing backlight]], which [[flicker (screen)|flicker]]s on and off at 240 Hz, once after every 120 Hz frame. The intent of a strobing backlight is to increase the apparent [[refresh rate|response rate]] and thus reduce blur, which results in clearer motion. However, this technique has little to do with actual framerate. For active 3D, this framerate is halved, and no motion interpolation or pulldown functionality is typically provided. 600 Hz is an oft-advertised figure for [[plasma TV]]s, and while technically correct, it only refers to an inter-frame response time of 1.6 milliseconds. This significantly reduces blur and thus improves motion quality, but is unrelated to interpolation and content framerate. There are no consumer films shot at 600 frames per second, nor any realtime [[video processor]]s capable of generating 576 interpolated frames per second.
==Software applications==
===Video playback software===
Motion interpolation features are included with several video player applications.
* [[WinDVD]] uses Philips' [[Trimension|TrimensionDNM]] for frame interpolation.<ref>
* [[PowerDVD]] uses TrueTheater Motion for interpolation of DVD and video files to up to 72 frame/s.<ref>{{cite web|url=http://www.cyberlink.com/stat/technology/enu/true-theater-solution.jsp|title=Video Enhancement – TrueTheater Technology|accessdate=2009-08-24|work=CyberLink}}</ref>
* Splash PRO uses Mirillis Motion² technology for up to Full HD video interpolation.<ref>{{cite web|url=http://mirillis.com/en/products/picture2.html |title=Picture2 |website=Mirillis.com |date=2010-07-01 |accessdate=2016-11-30}}</ref>
* DmitriRender uses GPU-oriented frame rate conversion algorithm with native DXVA support for frame interpolation.<ref>{{cite web|url=http://www.dmitriRender.ru/ |title=Home |website=DmitriRender.ru |date= |accessdate=2016-11-30}}</ref>
* Bluesky Frame Rate Converter is a DirectShow filter that can convert the frame rate using AMD Fluid Motion.<ref>{{cite web|url=http://bluesky23.yukishigure.com/en/BlueskyFRC.html |title=Bluesky Frame Rate Converter |website=Bluesky23.yukishigure.com |date= |accessdate=2016-11-30}}</ref>
* SVP (SmoothVideo Project) comes integrated by default with [[Media Player Classic|MPC-HC]]; paid version can integrate with more players, including [[VLC media player|VLC]].<ref>{{cite web|url=https://www.svp-team.com/w/index.php?title=Main_Page |title=SVP - 60 fps / 120 fps HFR motion interpolation for Windows, macOS in mpv, VLC, Plex |website=SVP-team.com |date= |accessdate=2018-02-06}}</ref>
===Video editing software===
Some [[video editing software]] and [[plug-in (computing)|plugins]] offer motion interpolation effects to enhance [[slow motion|digitally-slowed video]]. [[FFmpeg]] is a [[free software]] non-interactive tool with such functionality. [[Adobe After Effects]] has this in a feature called "Pixel Motion". AI software company Topaz Labs produces Video AI, a video upscaling application with motion interpolation. The effects plugin "Twixtor" is available for most major video editing suites, and offers similar functionality.
=== Neural networks ===
* [https://github.com/baowenbo/dain Depth-Aware Video Frame Interpolation]
* [https://github.com/myungsub/cain Channel Attention Is All You Need]
* [https://github.com/megvii-research/ECCV2022-RIFE Real-Time Intermediate Flow Estimation]
* [https://github.com/ltkong218/IFRNet Intermediate Feature Refine Network]
=== Gaming ===
Intended for latency intolerant applications, especially games, some use additional metadata from deep inside the [[graphics pipeline]] to lessen artifacts or speed performance. Except for Nvidia's, all are hardware-agnostic.<ref name="pcgw">{{Cite web |url=https://www.pcgamingwiki.com/wiki/Glossary:High-fidelity_upscaling |title=Glossary:High-fidelity upscaling |website=[[PCGamingWiki]] |access-date=2025-05-01}}</ref>
* [[Deep Learning Super Sampling|DLSS Frame Generation]] from [[Nvidia]]
* [[GPUOpen#Frame Generation|FSR Frame Generation]] from [[AMD]]
* [[AMD Fluid Motion Frames|Fluid Motion Frames]] from [[AMD]]
* [[Intel Arc#Intel XeSS|XeSS Frame Generation]] from [[Intel]]
==Side effects==
===Visual artifacts===
{{Main|Visual artifact}}
Especially on cheaper TV implementations, visual anomalies in the picture are more pronounced. Described by CNET's David Carnoy as a "little tear or glitch" in the picture, appearing for a fraction of a second. He adds that the effect is most noticeable when the technology suddenly kicks in during a fast camera pan. Television and display manufacturers refer to this phenomenon as a type of [[digital artifact]]. Due to the improvement of associated technology over time, such artifacts appear less obviously with higher-end and newer consumer TVs, though they will never be eliminated "the artifacts happens more often when the gap between frames are bigger".<ref name="Six things"/>
===Latency===
[[Input lag]] for general purpose motion interpolation itself is usually ~10 [[millisecond|ms]], though some implementations are more than 80 ms, which for TVs (except on some [[Samsung]] sets) is further exacerbated by the need to disable [[Display lag#Game mode|game mode]], imposing dozens to hundreds of ms of additional lag.<ref name="rting">{{Cite web |url=https://www.rtings.com/tv/tests/motion/motion-interpolation-soap-opera-effect |title=Our TV Motion Tests: Motion Interpolation |last=Di Giovanni |first=Nicholas |date=2021-08-31 |orig-date=2015 |website=[[RTINGS.com|RTINGS]] |access-date=2025-05-01}}</ref> All that is on top of the already poor lag inherent to most TVs even when optimally configured, compared to CRTs or gaming monitors. For dedicated gaming interpolation such as DLSS4 MFG, lag is 6-9 ms depending on multiplier, vastly dwarfed by the added lag of a slower internal render framerate.<ref name="techspot">{{Cite web |url=https://www.techspot.com/article/2945-nvidia-dlss-4/ |title=A Review of Nvidia's DLSS 4 Multi Frame Generation |last=Schiesser |first=Tim |date=2025-01-28 |website=TechSpot |access-date=2025-05-01}}</ref> Prototype techniques, similar to those already deployed in some [[asynchronous reprojection]] for [[virtual reality]], could cut overhead well below 1 ms, even when generating thousands of frames.<ref name="buster">{{Cite web |url=https://blurbusters.com/frame-generation-essentials-interpolation-extrapolation-and-reprojection/ |title=Frame Generation Essentials: Interpolation, Extrapolation, and Reprojection |last1=Erhard |first1=William Sokol |last2=Rejhon |first2=Mark |date=2023-07-03 |website=Blur Busters |access-date=2025-05-01}}</ref>
=== Soap opera effect ===
{{main|Soap opera effect}}
Some opposition against motion interpolation has arisen not because of artifacts, but from a dislike of fluidity itself in some or all content, whether synthetic or native.<ref name="wouk20190921">{{Cite web |url=https://www.digitaltrends.com/home-theater/what-is-the-soap-opera-effect-in-tvs-and-how-to-turn-it-off/ |title=What is the Soap Opera Effect? How to stop motion smoothing on your TV |last1=Bizzaco |first1=Michael |last2=Malcolm |first2=Derek |date=2025-01-20 |orig-date=2019-09-21 |website=Digital Trends |access-date=2025-05-01}}</ref> Because cheaper TV programs such as [[soap opera]]s tended to be shot in 60 Hz, whereas more prestigious works such as theatrical movies tended to be filmed in 24 FPS, [[high frame rate]] has a "soap opera effect" for critics.
==See also==
* [[Inbetweening]]
*[[Television standards conversion]]▼
* [[Motion compensation]]
* [[Motion interpolation (computer graphics)]]
* [[Flicker-free]]
▲* [[Television standards conversion]]
* [[3:2 pulldown]]
==References==
{{Reflist}}
==External links==
* [https://web.archive.org/web/20100621171635/http://videoprocessing.ucsd.edu/publications/Year_2010/2010_03_Lee.pdf High Frame Rate Motion Compensated Frame Interpolation in High-Definition Video Processing]
* [https://research.microsoft.com/apps/pubs/default.aspx?id=69174 A Low Complexity Motion Compensated Frame Interpolation Method]
[[Category:Display technology]]
[[Category:Video processing]]
[[Category:Interpolation]]
[[Category:Video]]
[[Category:Film and video technology]]
[[Category:Film post-production technology]]
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