feat(dlna): add activity tracking for DLNA playback

[cj12312021]

Summary

Adds time-based activity tracking for scenes played via DLNA, enabling play count, play duration, and resume time tracking similar to the web frontend.

Changes

• New ActivityTracker in internal/dlna/activity.go
• Uses existing trackActivity UI setting (no new config needed)
• Time-based tracking approach (elapsed session time / video duration)
• 5-minute session timeout to handle aggressive client buffering

Limitations

This is a heuristic-based approach with known limitations:

• Cannot detect actual playback position (only elapsed time)
• Cannot detect seeking or pause state
• Works best for linear playback

Testing

• Unit tests added in activity_test.go
• Manually tested with Pigasus VR Media Player

Could close #5710,

[cj12312021]

Also fixes the previously closed issue #3681. The solution in the PR does, in fact, infer playback activity by tracking the HTTP request. Without implementing a more involved AVTransport Service, this is likely the most optimal solution. The biggest limitation here, as mentioned earlier, is that the resume index won’t be very accurate if the user jumps between time indexes, but most DLNA services don’t make seeking forward or backward very convenient to begin with. I believe a similar implementation is used for Plex.

[feederbox826]

My rationale for closing 3681 was that to do actual accurate tracking, you would have to reverse-engineer the HTTP range headers into the video block chunks and convert that into timestamps

The PR does do DLNA tracking but also makes a lot of assumptions as to watch activity and behaviour of the person - watching from the beginning to the end of a file linearly and continuously

[cj12312021]

No shade was intended by my earlier message. I discovered the closed issue yesterday after taking another pass to look for the issue requesting this feature, which I was sure existed.

Based on my research, fine-grained support, like what we have on the front end, is possible. It would introduce a lot of complexity, which likely would not be worth the time investment. The level of support provided here provides the most bang for the buck and seems to be the approach favored by similar apps. I think most who turn activity tracking on would be happy with some level of DLNA support rather than no support.

Speaking personally now, my viewing habits when using DLNA do tend to be more linear.