In order to release it under the GPL (at least if you want people to be
able to distribute it), you have to release the uncompressed audio or video
Says who? You have to distribute the it in a form that's ready for editing. Even DV (digital video) is compressed, people use it all the time even professionally for editing and it's extremely lossy (miniDV is 4:1:1, beside the intraframe compression applied).
Most digital tape mediums don't even support lossless video. Neither the GPLv2 or GPLv3 say anything about lossless.
If you're editing the audio/video in some weird
format that you don't have a free tool for, this may be a problem.
If the content is generated, then yes you do, and yes it's a problem for people using proprietary toolchains to generate free content. This in my mind is an argument against using proprietary toolchains.
You do not, however, need to release tools already available under a GPL compatible license unless modifications are needed to generate the object code (your generated content).