All extensions

syntax-highlight — rendered with syntax highlighting (1435)
special-renderer — a dedicated preview card (456)
native-sufficient — macOS Quick Look already handles it (115)
not-a-file — not a standalone file: URI schemes, container atoms, system artifacts (46); documented for reference, nothing to preview
gap — not yet supported; the honest backlog (3031)

video (83)

.rvx — RealVideo document Dedicated rendererrare
.srt — SubRip Subtitle Dedicated rendereruniversal
.ssa — Advanced SubStation Alpha Dedicated renderercommon
.sup — Blu-ray PGS Subtitle Dedicated renderercommon
.ttml — Timed Text Markup Language Dedicated renderercommon
.viv — Vivo video Dedicated rendererrare
.vivo — Vivo video Dedicated rendererrare
.vtt — WebVTT Subtitle Dedicated rendereruniversal
.webm — WebM Video Dedicated renderercommon
.wmx — Windows Media Redirector Dedicated rendererrare
.wpl — Windows Media Playlist Dedicated renderercommon
.zpl — Zune Playlist Dedicated rendererniche
.scc — Scenarist Closed Caption Syntax highlightedcommon
.smi — Synchronized Multimedia Syntax highlightedniche
.smil — Synchronized Multimedia Syntax highlightedniche
.ts — MPEG Transport Stream Syntax highlightedcommon
.3g2 — 3GPP2 Multimedia Handled by macOS itselfcommon
.3gp — 3GPP Multimedia Handled by macOS itselfcommon
.asf — Advanced Systems Format Handled by macOS itselfcommon
.avc — Advanced Video Coding Handled by macOS itselfcommon
.divx — DivX Video Handled by macOS itselfrare
.h264 — Advanced Video Coding Handled by macOS itselfcommon
.h265 — High Efficiency Video Handled by macOS itselfcommon
.hevc — High Efficiency Video Handled by macOS itselfcommon
.m1v — MPEG Elementary Stream Handled by macOS itselfcommon
.m2p — MPEG-2 Stream Handled by macOS itselfcommon
.m2t — MPEG-2 Stream Handled by macOS itselfcommon
.m2ts — AVCHD Video Handled by macOS itselfcommon
.m2v — MPEG Elementary Stream Handled by macOS itselfcommon
.mov — QuickTime video Handled by macOS itselfuniversal
.mp4 — MPEG-4 video Handled by macOS itselfuniversal
.mpeg — MPEG-1 or MPEG-2 video stream, the ISO standard format used on DVDs and early digital video Handled by macOS itselfuniversal
.mpg — MPEG-1 or MPEG-2 video stream, the ISO standard format used on DVDs and early digital video Handled by macOS itselfuniversal
.tp — Transport Stream Handled by macOS itselfcommon
.trp — Transport Stream Handled by macOS itselfcommon
.vob — DVD Video Object Handled by macOS itselfcommon
.wmv — Windows Media Video Handled by macOS itselfuniversal
.aaf — Advanced Authoring Format, a multimedia file format from Avid for professional video post-production and interchange Not yet supportedcommon
.ari — ARRI RAW Not yet supportedniche
.bdmv — Blu-ray Movie Directory Not yet supportedcommon
.braw — Blackmagic RAW Not yet supportedcommon
.clpi — Blu-ray Clip Info Not yet supportedcommon
.cpi — AVCHD Clip Info Not yet supportedcommon
.dvr-ms — Windows Recorded TV Not yet supportedniche
.edl — Edit Decision List Not yet supportedcommon
.f4m — Flash Media Manifest Not yet supportedrare
.fxm — JavaFX video Not yet supportedrare
.idx — VobSub Index Not yet supportedcommon
.idx1 — AVI Index Chunk Not yet supportedcommon
.ism — IIS Smooth Streaming Not yet supportedniche
.ismc — IIS Smooth Streaming Not yet supportedniche
.ismv — IIS Smooth Streaming Not yet supportedniche
.ivf — Indeo Video Format Not yet supportedniche
.m1u — Video playlist Not yet supportedrare
.m4u — Video playlist Not yet supportedrare
.mjpeg — MJPEG video stream Not yet supportedrare
.mjpg — MJPEG video stream Not yet supportedrare
.mk3d — Matroska 3D Video Not yet supportedniche
.mpd — MPEG-DASH Manifest Not yet supportedcommon
.mpl — AVCHD/Blu-ray Playlist Not yet supportedcommon
.mpls — AVCHD/Blu-ray Playlist Not yet supportedcommon
.mxu — Video playlist Not yet supportedrare
.ogv — Ogg Video Not yet supportedniche
.r3d — REDCODE RAW Not yet supportedcommon
.spl — FutureSplash Animation Not yet supportedrare
.sub — MicroDVD / SubViewer Not yet supportedcommon
.swf — Shockwave Flash Not yet supportedrare
.uuid — MP4 User Extension Atom Not yet supportedcommon
.vpj — VideoPad Project Not yet supportedniche
.vpr — Vegas Pro Project Not yet supportedcommon
.wlmp — Windows Live Movie Maker Not yet supportedrare
.wtv — Windows Recorded TV Not yet supportedniche
.wvx — Windows Media Video Redirector Not yet supportedrare
.y4m — YUV4MPEG2 raw video stream, read by ffmpeg and video processing tools Not yet supportedniche
.yt — YouTube media archive Not yet supportedrare
.avih — AVI main header chunk, the RIFF structure at the start of every Audio Video Interleave file Not a file (scheme/atom)rare
.ftyp — MP4 File Type Atom Not a file (scheme/atom)rare
.matroska — EBML header chunk, the binary master element starting every Matroska media container Not a file (scheme/atom)rare
.mdat — MP4 media data atom holding the raw audio and video samples of an MP4 file Not a file (scheme/atom)rare
.moov — MP4 metadata atom indexing the tracks and sample tables of an MP4 media file Not a file (scheme/atom)rare
.movi — AVI Movie Data Chunk Not a file (scheme/atom)rare
.stbl — MP4 Sample Table Atom Not a file (scheme/atom)rare
.strl — AVI Stream List Chunk Not a file (scheme/atom)rare