Support for KLV Metadata / EMSG Delivery (MISB ST 1910)

[jordanOWA]

Hi All -

I've heard rumor an upcoming release of dash.js will include support for processing KLV metadata included within emsg boxes per MISB ST 1910. Does anyone know if this is true? If so, is there an estimated release version / date? Is there a beta version available?

Thank you in advance for any additional insight. I am very interested in implementing this capability into several of our online DASH players in order to support processing MISB ST 601.X compliant KLV metadata from an unmanned aerial system (UAS).

Thanks,

Jordan

[dsilhavy]

Hi,
dash.js supports EMSG events with custom scheme_id_uri paramters. We dispatch everything to the underlying application. I have not studied the specification but KLV metadata seems to use a custom scheme_id_uri with corresponding values. Consequently, you can register for those types of events using callbacks. An example can be found here: http://reference.dashif.org/dash.js/nightly/samples/advanced/listening-to-SCTE-EMSG-events.html

player.on(SCHEMEIDURI, showStartEvent, null); /* Default mode is onStart, no need to specify a mode */
player.on(SCHEMEIDURI, showReceiveEvent, null, { mode: EVENT_MODE_ON_RECEIVE });

Timing wise we support version 0 and version 1 events.

There was also a short discussion on KLV events in this thread: #3429

[jordanOWA]

@dsilhavy, thanks for the previous reply - I am finally getting back around to this project and am now up and running with using the eMsg boxes to receive the KLV metadata.

Unfortunately, the metadata I'm working with is all asynchronous - the metadata eMsg boxes are delivered all together at the front of the CMAF fragment and the eMsg boxes do not contain a presentationTime (NaN). This presents a challenge of syncing the metadata back to the video and aligning the KLV Precision Time Stamp (PTS) field to the appropriate video presentation time. My ultimate goal is to display the synced video and KLV values on a webpage.

I have attempted to map the KLV's PTS to a specific player time (i.e. XX seconds into the video) during the initial reading of the eMsg boxes. This associates a respective player time (in the future) to each KLV value - in other words, assigning each KLV chunk of data to a future video timestamp at which it should be displayed on the webpage (in sync with the video).

First off, does this seem like the best approach?

Next, I would like to assign a time based callback function to the player - basically telling it, "hey, at this specific time (i.e. the time previously mapped to a KLV dataset), call this function" so that the corresponding metadata can be printed to the screen. Is this possible? Is there a better approach?

Again, my thanks to the community for their help.

[jordanOWA]

Bump to previous message...anyone have any recommendations on how to schedule a callback to a specific future playback time?

Thanks!

[dsilhavy]

@jordanOWA

• Regarding the question about callback to a specific time. You could use http://cdn.dashjs.org/latest/jsdoc/MediaPlayerEvents.html#event:PLAYBACK_TIME_UPDATED and register a callback function. In this callback function you can check if the target time is reached.