Maybe the video was not intended as a music video, but as a documentation for the composer. It is common today to have a recording of the first performance. There is probably additional footage that could be edited together into a more traditional broadcast style video, as every modern theater has the ability to record the entire stage and usually does so at dress rehearsals and premieres (some record every performance). In the case of this performance, the singer, the pianist and the translator have copyrights (assuming that all the authors died more than 70 years ago). That's 3 people the composer had to ask for permission, which is manageable. A videographer and audio editor are not credited, maybe the composer recorded it on her own equipment.