Fix/seek near period end

[lkinasiewicz]

Addresses issue #3713

[dsilhavy]

@lkinasiewicz Thank you for the work on this. I had a quick look, and I am afraid this will not work for live multiperiod. You can check with this stream for instance: https://d24rwxnt7vw9qb.cloudfront.net/v1/dash/e6d234965645b411ad572802b6c9d5a10799c9c1/All_Reference_Streams/4577dca5f8a44756875ab5cc913cd1f1/index.mpd

We use the DashHandler logic to decide whether a period is finished or not. In the case of live the changes in DashHandler will never finish a period:

        // for dynamic manifest, more segments will be available after manifest update
        if (isDynamicManifest && !dynamicStreamCompleted) {
            return false;
        }

In addition, i think we break track switches with the changes made here.

I started improving the DashHandler logic as well, based on the email thread we had. My changes are visible here: https://github.com/Dash-Industry-Forum/dash.js/tree/feature/dashHandlerOptimizations
The changes I made there should fix parts of #3713.

I suggest we wait for my PR to be finished and merged and then check your changes regarding the seek on top of my PR.

[lkinasiewicz]

Well... good point 🤦 Your changes look like they should fix the problem in DashHandler so let's wait with this one.

[lkinasiewicz]

I have removed changes in DashHandler and left only the rest. When I applied my changes on top of #3727, I could not reproduce the problem reported in #3713.

[lkinasiewicz]

@dsilhavy can you please have a look at the changes?

[dsilhavy]

@lkinasiewicz Thanks for your work on this, based on the recent changes we made to the scheduling I provided a first draft of a fix for the seeking problem here: #3772 . Can you please check on your side if this solves the problem.

We should only adjust the seek target if we dont find a valid request.