Enhance media overlays in epub 3 specification ?

Hello,

I have two questions/propositions regarding media overlays.

I have checked in the recent v 3.1 of the spec and it seems that this topic is not addressed.

1) As the media type video/mp4 is supported by epub, why not considering only the audio track of the video for being synchronized with the text read ?

e.g:

In the .opf file:

<item id="video1" href="video.mp4" media-type="video/mp4"/>

In the .smil file :

<par id="..">
<text src=".."/>
<audio src="video.mp4" clipBegin=".." clipEnd=".."/>
</par>

2) To go a little further, why finally the <video> element couldn't be supported in the .smil file ? :

<par id="..">
<text src=".."/>
<video src="video.mp4" clipBegin=".." clipEnd=".."/>
</par>

The video could be displayed somewhere in the xhtml of the page with a :

<video src="video.mp4" poster=".." width=".." height=".."/>

allowing that both image and sound are synchronized with the text.

Thank you.

Best regards.