Add correct support of audio element

[nicosang]

Hi,

this PR has to solve issue #2490. Unit tests have been also updated by adding checking of element type.
@VincentFTS, could you, please, take a look at this PR?

Many thanks,
Nico

[davemevans]

This seems like a bit of a hack to me. Additionally, there doesn't seem to be a similar option if I want the player to ignore audio when playing in a video element. #2490 admits that the issue is caused when trying to hack round another problem. Further it looks like if you want to preload and attach a media element later, dash.js still preload all the video?

Ultimately, IMO, the top level application should only be passing audio-only manifests to the player when it knows the media element is of type audio.

That said, if this is a problem we want to solve in the general case, perhaps it would be better to have an explicit configuration option to ignore streams of a particular MIME type?

[nicosang]

Hi @bbcrddave ,

there is many points that attempt to be fix with this PR. First of all, I think we do agree together to add tests on the type of element that is used by SetElement. The video element is able to play both audio and video, so, according to me, it is not useful to have same behavior than with the audio element.

You're right, in preload use case, we don't know if the element will be an audio or a video so, we can't filter correctly. So, indeed, a configuration option could be interesting to add....

Nico

[davemevans]

For clarity, I meant the application controlling dash.js should know what the element type is, and only select appropriate content to be presented, rather than dash.js making the decision. That application is more likely to be aware of the context of the page, and so could either configure dash.js appropriately, or only select appropriate content.

In the past (#1309) we have removed code detecting the object type since it would break, for example, the use case where vendors create an <object> which has an API compatible with HTMLMediaElement. In this case, the nodeName would be OBJECT, which would not pass this test. It's probably less important more recently I guess.

Anyway, I don't feel that strongly - was just making the case for an alternative solution 😄

[VincentJousse]

@nicosang ,
thank you, it works !

@bbcrddave
Imagine a context where the application needs to play some film soundtracks, it would be a pity to have to create a specific manifest whereas the "original" film manifest contains everything needed.
I agree that making dash.js configurable about this may be an elegant solution ;)