Version 1 event messages appear late in media timeline

[mpegdash-user]

When using version 1 event messages, their presentation time in the media timeline is bumped out (roughly) double the expected time from the start time.

When playing video with inband version 1 event messages (emsg), theDashAdapter.js code uses version 0 logic and adds the presentation_time_delta field of the eventBox object to the presentation time of the current segment to create the presentationTime for the event.

// grab the presentation time delta
const presentationTimeDelta = eventBox.presentation_time_delta;
... // then use it to calculate a presentation time in the future.
const presentationTime = startTime * timescale + presentationTimeDelta;

The code overloads the eventBox.presentation_time_delta field such that it contains the presentation_time_delta for version 0 event messages and presentation_time for version 1 event messages.

Propose modifying the code to treat the presentation_time_delta variable differently depending on the version of event message box you are using. Here is a diff:

302c302,308
diff orig/DashAdapter.js new/DashAdapter.js
<         const presentationTimeDelta = eventBox.presentation_time_delta;
---
>         if (eventBox.version === 0 ) {
>           const presentationTimeDelta = eventBox.presentation_time_delta;
>           const presentationTime = startTime * timescale + presentationTimeDelta;
>         } else {
>           const presentationTimeDelta = 0;
>           const presentationTime = eventBox.presentation_time_delta;
>         }
306c312
<         const presentationTime = startTime * timescale + presentationTimeDelta;
---
>

This produces the expected behavior.

Environment

• [x] The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• [x] The stream has correct Access-Control-Allow-Origin headers (CORS)
• [x] There are no network errors such as 404s in the browser console when trying to play the stream
• [x] The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• [x] The issue occurs in the latest reference client on http://reference.dashif.org/dash.js/ and not just on my page
• Link to playable MPD file:
• Dash.js version: 3.0.2
• Browser name/version: Chrome 80.0.3987.132 and Microsoft Edge 44.17763.1.0
• OS name/version: Windows 10

Steps to reproduce

1. create a video stream composed of multiple 2 second segments
2. place two (2) version 1 emsg boxes at the beginning of each segment. The presentation_time should be set to (segment number) * (segment duration.)
3. be sure to modify your .mpd file to signal inband events: <InbandEventStream schemeIdUri="urn:scte:scte35:2013:xml";" value="999" />
4. modify the samples/advanced/listening-to-SCTE-EMSG-events.html page

• point the URL constant to your dashlivesim address.

Observed behaviour

1. Load the modified events.html page.
2. Move the timebar scrubber to time 00:00:00.
3. Allow the video to play for a few seconds.
4. You should see a notification at time 00:00 with PresentationTime 00000 and PresentationTimeDelta 00000
5. a notification will probably not appear at time 00:01
6. the notification at time 00:02 will have PresentationTime 180000 and PresentationTimeDelta 90000
7. a notification will probably not appear at time 00:03

[dsilhavy]

@mpegdash-user Can you provide a sample stream with version 1 emsg boxes?

[dsilhavy]

I will defer that until we have a testvector

[dsilhavy]

Implemented here https://github.com/Dash-Industry-Forum/dash.js/pull/3325, thanks