Just came across a bug, while trying to use a 'Video' Qml type in my QML offscreen renderer. Error description was 'Failed to find shader biplanaryuvvideo_core.frag' and 'Failed to find shader biplanaryuvvideo_core.vert'.
Turns out that rendering QML to a QSurfaceFormat::CoreProfile always appends '_core' to the shader source names, and no such shaders are present in 'qtmultimedia/src/qtmultimediaquicktools/shaders'. Check QSGShaderSourceBuilder::appendSourceFile(const QString &fileName)
which in turn calls resolveShaderPath(fileName) that does the appending of '_core'. IMHO proper solution would be to add the *_core files to the shaders in 'qtmultimedia/src/qtmultimediaquicktools/shaders'.
Until a fix to the issue, using QSurfaceFormat::CompatibilityProfile profile, solves the issue.