Section 7.2 of the current draft adds MediaPlaybackQuality to the HTMLMediaElement.  These can be audio only, in which case the frame quality metrics shouldn't apply.

Recommend replacing HTMLMediaElement with HTMLVideoElement in 7.2:

7.2 New Attributes and Behavior

This section specifies new attributes and internal state that are being added to the HTMLVideoElement.

Each HTMLVideoElement will maintain a total video frame count variable that keeps track of the total number of frames that have been displayed and dropped. This variable is initialized to 0 when the element is created and whenever the media element load algorithm is invoked. It is incremented when a video frame is displayed or when the dropped video frame count is incremented.

Each HTMLVideoElement will maintain a dropped video frame count variable that keeps track of the total number of frames that have been dropped. This variable is initialized to 0 when the element is created and whenever the media element load algorithm is invoked. It is incremented when a video frame is dropped predecode or when a frame is decoded but dropped because it missed a display deadline.

partial interface HTMLVideoElement{
    readonly    attribute MediaPlaybackQuality playbackQuality;
};

This paragraph is a subparagraph of 7. HTMLMediaElement Extensions, which makes this fit a little awkward.  It fully describes the requested change though.