dash.js profiles for specific platforms

[dsilhavy]

Description

dash.js uses the Media Source Extensions (MSE) and the Encrypted Media Extensions (EME) for playback of ABR content. Both MSE and EME are available on a variety of platforms such as Desktop Browsers, SmartTVs, Set-Top boxes, mobile phones and tablets. Typically, such devices perform very differently.

Differences on such platforms might occur in terms of the supported APIs, speed and performance, or even bugs on the platform itself. To overcome platform specific issues dash.js offers a variety of different configurations options.

The idea of this thread is to discuss the introduction of dash.js profiles tailored for playback on specific devices. As an example, there might be a profile "SmartTV" that adjusts the buffer settings of dash.js to run in a more performant manner compared to the default settings.

Discussion items

• Does this approach make sense in general?
• What settings are currently used by dash.js users on specific platforms like SmartTVs?
• How do we want to expose the different profiles? Should this be plain application logic or should there be an endpoint in dash.js itself?

[Murmur]

See this issue on one of the biggest TV manufacturers. TTML subtitles track is never mode=showing so dashjs does not render anything.
HbbTV-Association/ReferenceApplication#79 (comment)

Our internal test version uses this hardcoded hack to overcome the problem as an unofficial validation purpose. This problem may relate to a native texttrack object being used for ttml subtitles(?).
Dashjs does not use a texttrack for webvtt but instead use a "pure app javascript" rendering? Similar approach for ttml would be nice.

TextTracks:
function _handleHtmlCaption(currentItem, timeOffset, track) {
   //if (track.mode === "showing") {
   if (track.mode === "showing" || track.mode === "hidden") {
      _renderCaption(this);
      ...

[matt-stephenson]

The HbbTv specification details how much data the SourceBuffers should be able to accept. For Smart TV's, we base our buffer settings on this.

https://www.etsi.org/deliver/etsi_ts/102700_102799/102796/01.07.01_60/ts_102796v010701p.pdf (section 9.6.13)