This is fixed by applying https://bitbucket.org/acoustid/chromaprint/commits/90822f6eee64da2941c9cbd9cd41a9664fead1d4 The "tools" USE flag is required by media-sound/picard, breaking that application too. Reproducible: Always Steps to Reproduce: Install media-video/libav-0.8.7 and emerge chromaprint.
Created attachment 367908 [details] build log
Created attachment 367910 [details, diff] fix
Putting the patch in my /etc/portage/patches/ fixed the issue.
The libav code requires libav-9.10, for now. It was a quick hack, and uses deprecated methods. I'm working on an update for libav master; I'll try to add libav-0.8 while I'm at it.
applied the patch in portage. still builds fine with media-video/ffmpeg, so i'm happy.