As seen in this upstream GStreamer bug there is an issue with the VP8 encoder in 1.2.0 making it so slow it is useless: https://bugzilla.gnome.org/show_bug.cgi?id=722332 This can be resolved by updating to either 1.2.2 or 1.3.0. There is no 1.2.2 tarball, but there is a git tag.
libvpx-1.3.0-1.fc19 has been submitted as an update for Fedora 19. https://admin.fedoraproject.org/updates/libvpx-1.3.0-1.fc19
libvpx-1.3.0-2.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/libvpx-1.3.0-2.fc20
Package libvpx-1.3.0-2.fc20: * should fix your issue, * was pushed to the Fedora 20 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing libvpx-1.3.0-2.fc20' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2014-2349/libvpx-1.3.0-2.fc20 then log in and leave karma (feedback).
libvpx-1.3.0-3.fc19 has been submitted as an update for Fedora 19. https://admin.fedoraproject.org/updates/libvpx-1.3.0-3.fc19
libvpx-1.3.0-3.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/libvpx-1.3.0-3.fc20
libvpx-1.3.0-3.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.
libvpx-1.3.0-3.fc19 has been pushed to the Fedora 19 stable repository. If problems still persist, please make note of it in this bug report.