Low latency playback does not accurately estimate throughput, uses too high quality level

[sandersaares]

Environment

• The MPD passes the DASH-IF Conformance Tool on https://conformance.dashif.org/
• The stream has correct Access-Control-Allow-Origin headers (CORS)
• There are no network errors such as 404s in the browser console when trying to play the stream
• The issue observed is not mentioned on https://github.com/Dash-Industry-Forum/dash.js/wiki/FAQ
• 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: https://streams.ml.mdn.skype.net/stream/teststream-01/manifest.mpd?throughputLimitKbps=1500
• Dash.js version: nightly
• Browser name/version: Edge 88
• OS name/version: Windows 10 20H2

Steps to reproduce

1. Start playback in reference player with settings:
   • low-latency mode: yes
   • initial live delay: 1
   • ABR algorithm: throughput or BOLA or L2A or LoL+
2. Wait 30 seconds.

Observed behavior: general

For the L2A/LoL algorithms, player estimates throughput at 2000+ Kbps, which is far above server-enforced limit of 1500 Kbps. Choice of throughput estimation method does not appear to make any difference as far as I can tell.

For the BOLA/throughput algorithms, quality level is just stuck at minimum all the time. I assume these are not tuned for low-latency but include them here for completeness - what I care about is low latency behavior here.

Observed behavior: L2A ABR

With L2A ABR algorithm: player constantly stalls. Player tries to use 1500 Kbps quality level, which does not fit within 1500 Kbps budget (when added audio + overheads).

Observed behavior: LoL+ ABR

With LoL+ ABR algorithm: player constantly speeds up and slows down as it is unable to maintain buffer level. Player often tries to use 1500 Kbps quality level and occasionally drops down briefly.

Observed behavior: Throughput ABR

With "throughput" ABR algorithm: player is stuck on minimum quality level (250 kbps).

Observed behavior: BOLA ABR

With BOLA ABR algorithm: player is stuck on minimum quality level (250 kbps).

Expected behavior

Maintain stable 1000 Kbps quality level.

(Screenshot with manually selected quality level)

[mlasak]

Thanks @sandersaares for raising this issue. We have been able to reproduce, identified the root for this problem and are working on a solution to this.

[mlasak]

Hi @sandersaares, with out new throughput measurement method the low latency streaming looks like this

Will raise a PR for review, after GUI part for selecting the new method is added.

[akouSDN]

Thanks for reporting this issue in LoL+ bandwidth measurements. PR 3663 addresses this issue

[stale]

This issue has been automatically marked as stale because it has not had recent activity. However, it might still be relevant so please leave a short comment if it should remain open. Otherwise the issue will be closed automatically after two weeks. Thank you for your contributions.

[dsilhavy]

unstale

[stale]

This issue has been automatically marked as stale because it has not had recent activity. However, it might still be relevant so please leave a short comment if it should remain open. Otherwise the issue will be closed automatically after two weeks. Thank you for your contributions.

[stale]

This issue has been automatically closed because no further activity occurred. If you think this issue is still relevant please reopen it or contact @dsilhavy. Thank you for your contributions.

[dsilhavy]

This issue appeared again at MHV 24. The estimated throughput was higher than the expected one.