When sympathy gets a file, it checks three things in order and stops at the first no.

the extension is on the list: ivf, obu, mp4, m4v, mov, mkv, webm, avi, mj2, apv, mxf. anything else goes straight to premiere.

there's a decoder for the codec. if the container doesn't say which codec it is, sympathy tries the likely ones and keeps the first that gives a picture.

it isn't a format premiere handles itself. those go back to premiere.

if all three pass, sympathy opens the file. if not, the file goes back to premiere as is, and if premiere can't open it either, it won't open.

a file can also be turned down because it can't be read, has no video track (like an audio-only .mxf from a dcp or imf package), has no decoder, or has an unnamed codec that nothing could decode.

Formats

av1, vp9 and vp8 in any container except .ivf and .obu. h.264, hevc and prores in .mkv and .webm.

.mkv and .webm with any codec sympathy can decode, vvc and ffv1 included.

av1 in .mp4, .ivf and .obu. apv in .mov and .mp4.

jpeg 2000 in .mov and .mj2. ffv1 in .mov.

cineform, grass valley hqx and canopus hq, hqa and cllc in .avi.

mpeg-2 in .mov and .avi.

utvideo, huffyuv, ffvhuff and magicyuv in any container.

uncompressed v410 in .mov and .avi, r10k in .avi, 8-bit bgra in .mov.

in .mxf, h.264 high profile, panasonic avc-intra in op-atom, and files whose essence premiere can't identify.

Install

run Sympathy Setup.exe. it finds premiere's MediaCore folder and installs the plug-in into MediaCore\Sympathy.

to uninstall, go to installed apps in windows settings.