How to import WebM / vp9 / vp09 / vp8 format

There are a lot of posts about this, many with suboptimal answers, so I'm going to post what I've learned, and add links to here from all the other posts I've seen.

You don't need to convert the file to a different codec to import. That would obviously degrade quality, as well as being an extra step.

Some people have noted that WebM formats are designed for content delivery, not editing, and using them for editing may be inefficient. The best solution for this is proxying, not converting to a different format before importing. (Of course if the video was originally recorded in some other format, and converted to WebM, it is better to get the original files if possible.)

The free WebM plugin from Fnord supports importing (decoding), not just exporting, although they don't mention this in its description. You can install the plugin from the Creative Cloud desktop app or by downloading it from the Fnord site.

Once installed, the plugin will automatically be used whenever you try to import a file with the .webm extension. If a file has a different extension but uses one of the WebM codecs (vp8 or vp9), you'll still get an error message about an unsupported codec.

The file must use either the vp8 or the vp9 video codec, AND either the Ogg Vorbis or the newer Opus audio codec. If the file uses a different audio codec, the plugin will give an error message.

I've seen files with extension ".ts.mp4" that contain video in vp9 and audio in AAC (from Android phones, or downloaded from Google hosting). To import this you do need to convert something. My solution is to use ffmpeg to convert the audio to Opus while copying the video stream (NOT decoding and re-encoding the video, which would degrade quality). Command line:

ffmpeg -i inputfile.ts.mp4 -c:v copy -c:a libopus -b:a 510k outputfile.webm

This will degrade the audio quality a bit, although it uses the maximum bit rate for Opus, which is very good quality. If you want absolute best quality in both video and audio, you should be able to create a separate audio file with just the AAC stream, import that along with the video, and sync them up. The ffmpeg command for this would be something like:

ffmpeg -i inputfile.ts.mp4 -c:a copy outputaudiofile.aac

(Not sure .aac is really the correct file extension for that, but it seems to work in Premiere.)