Textures for NV12 and NV21 video frames use RG8 formats, which on GLES2 RHI implementation are translated to GL_RG8 internal format. GLES 2.0 doesn't support this format, so some workaround is needed to support these pixel formats.

QTBUG-114104 is related, with focus on getting a workaround for a similarly unsupported GL_R8 format for YUV420P, YUV422P, YV12, IMC1-4 and Y8, and partially to NV12 and NV21.