The media-video/xawtv-3.73-r1 ebuild wants to use quicktime4linux. Since version 3.73, quicktime4linux has been dropped for libquicktime (http://libquicktime.sf.net). As a result, xawtv will not include quicktime support when emerged.
3.78 depends on libquicktime now, with the quicktime USE flag. thanks for the heads up.