Emergency switch to lower bandwidth rendition on aborted fragment load not working

[CaseV7]

What version of Hls.js are you using?

v1.5.0-beta.3

What browser (including version) are you using?

Firefox

What OS (including version) are you using?

MacOS 13.5.1

Test stream

No response

Configuration

{
  "debug": true,
  "enableWorker": true,
  "lowLatencyMode": false,
  "backBufferLength": 60,
   "fragLoadPolicy": {
    "default": {
      "maxTimeToFirstByteMs": 6000,
      "maxLoadTimeMs": 15000,
      "timeoutRetry": {
        "maxNumRetry": 10,
        "retryDelayMs": 0,
        "maxRetryDelayMs": 0
       },
      "errorRetry": {
        "maxNumRetry": 5,
        "retryDelayMs": 3000,
        "maxRetryDelayMs": 15000,
        "backoff": "linear"
      }
    }
  }
}

Additional player setup steps

The player is in "auto" mode.

Checklist

• The issue observed is not already reported by searching on Github under https://github.com/video-dev/hls.js/issues
• The issue occurs in the stable client (latest release) on https://hlsjs.video-dev.org/demo and not just on my page
• The issue occurs in the latest client (main branch) on https://hlsjs-dev.video-dev.org/demo and not just on my page
• 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

Steps to reproduce

1. Load a stream as normal and get a full buffer
2. Flip on Network link conditioner to cause timeouts (Setting the download "Bandwidth" to something small that allows small segments to transfer in less than 15 seconds, but causes high resolution segments to timeout)

Expected behaviour

HLS.js should emergency switch down to the lowest bandwidth rendition to continue playback.

What actually happened?

Playback stalls.

In the console there is an attempted switch to 0:

[abr] Fragment 264 of level 4 is loading too slowly; Time to underbuffer: 0.000 s Estimated load time for current fragment: 0.291 s Estimated load time for down switch fragment: 0.071 s TTFB estimate: -1 Current BW estimate: 406592.719 Kb/s New BW estimate: 406592.719 Kb/s Aborting and switching to level 0

Then there are a bunch of lines showing the player attempting to switch from 4->4 (which doesn't work).

[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 [abr-controller.ts:814:17](https://04777092.hls-js-dev.pages.dev/dist/src/controller/abr-controller.ts)

[info] > [abr] buffer is empty, optimal quality level 4

Console output

Error event: 
Object { type: "networkError", details: "fragLoadTimeOut", fatal: false, frag: {…}, error: Error, networkDetails: XMLHttpRequest, stats: {…}, errorAction: {…} }
​
details: "fragLoadTimeOut"
​
error: Error: Timeout after 6000ms
​
errorAction: Object { action: 5, flags: 0, retryCount: 6, … }
​
fatal: false
​
frag: Object { _url: "https://media-production.nebula.app/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE3MDQ0ODk3MDh9.3hbZer9X_cpqpTOYzR52d5yqRlDKcYzwTZqpwgROAJ0/nebula-content/videos/74cd1841-5714-4480-b0d1-51da9310fdbd/video_upload:fb88040a-73c9-49ba-8fc2-f9b3de3cd0d1/audio/en/mp4a.40.2/seg-266.m4s", baseurl: "https://media-production.nebula.app/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJleHAiOjE3MDQ0ODk3MDh9.3hbZer9X_cpqpTOYzR52d5yqRlDKcYzwTZqpwgROAJ0/nebula-content/videos/74cd1841-5714-4480-b0d1-51da9310fdbd/video_upload:fb88040a-73c9-49ba-8fc2-f9b3de3cd0d1/audio/en/mp4a.40.2/media.m3u8", relurl: "seg-266.m4s", … }
​
networkDetails: XMLHttpRequest { readyState: 0, timeout: 0, withCredentials: false, … }
​
stats: Object { aborted: true, loaded: 0, retry: 0, … }
​
type: "networkError"
​
<prototype>: Object { … }
main.js:734:12
Error event: 
Object { type: "mediaError", details: "bufferStalledError", fatal: false, error: Error, buffer: 0, errorAction: {…} }
​
buffer: 0
​
details: "bufferStalledError"
​
error: Error: Playback stalling at @1584.019875 due to low buffer ({"len":0,"start":1584.019875,"end":1584.019875})
​
errorAction: Object { action: 0, flags: 0 }
​
fatal: false
​
type: "mediaError"
​
<prototype>: Object { … }
main.js:734:12
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[log] > [stream-controller]: Level 0 loaded [0,379][part-379--1], cc [0, 0] duration:2276.5833333333335 stream-controller.ts:638:9
[log] > [stream-controller]: WAITING_LEVEL->IDLE base-stream-controller.ts:1779:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4 abr-controller.ts:588:11
[log] > [stream-controller]: Loading fragment initSegment cc: 0 of [0-379] level: 0, target: 0 base-stream-controller.ts:746:9
[log] > [stream-controller]: IDLE->FRAG_LOADING base-stream-controller.ts:1779:11
[log] > [stream-controller]: FRAG_LOADING->IDLE base-stream-controller.ts:1779:11
[info] > [abr] switch candidate:4->4 adjustedbw(395533397)-bitrate=376465802 ttfb:0.0 avgDuration:6.0 maxFetchDuration:4.0 fetchDuration:0.3 firstSelection:false codecSet:avc1,mp4a videoRange:SDR hls.loadLevel:0 abr-controller.ts:814:17
[info] > [abr] buffer is empty, optimal quality level 4

Chrome media internals output

No response