FOMS [SF] October 2019

See schedule for more session notes http://www.foms-workshop.org/foms2019SF/pmwiki.php/Site/Schedule

Monday 10/21

Position Statement

Rob Walch - JW Player, Web Player Principal

• Low-Latency
  • MSE v2 (codec transition)
  • Bandwidth Estimation (+ABR)
  • fetch in worker (which browsers support it)
  • LL Workflow
    • fetch/xhr issue: H/2 byte-ranges never cached
• Player Benchmarking
  • Performance Resource Timing (resources, first paint, long task observers)
  • Video playback quality
• WebVTT / IMSC1
• • MetaData (SCTE, DATERANGE, Cross-Browser)
    • Frame accurate
• Error Handling
  • Specific segment (or url)

Lightning Talk: Will Law Common-Media-Client-Data

• CTE spec for Player to tell CDN what it needs and how it's doing *Coming soon: Common-Media-Server-Data

MSE v2

Wolz:

• Main features (not yet available)
  • MSE available in worker context
    • ObjectUrl context creation in the Worker (pass it to main thread)
    • need buffered and currentTime from BufferSource and MediaElement in main thread
  • Chrome Origin trial this/next quarter
  • Firefox / Safari to follow
• API for standardizing interop around gaps
  • w3c/media-source#160
  • allow gaps? on which tracks?
    • minimum jump
    • play-through
  • pops with audio gaps
  • Tell SourceBuffer how to deal with gaps (configure buffer)

v-Next:

• Appending small amounts of data (frames)
  • Chrome does 128k at a time
  • Scheduling overhead
  • Does byte-stream format have to be one mp4
  • GOP based? Frame based
  • Min playback buffer to player "canplay"?
    • ~3 frames, 200ms audio in Chrome
    • 2-3 seconds
    • ~30 frame latency in Edge
• Chrome latency hint
  • Byte stream can say it's live to just play
• Minimum playback buffer
  • See Exo play when ready (load control determines "ready" or "canplay" / have future data or autoplay has enough)
  • Shaka sets playbackRate to 0 to wait for more data
• Auto EMSG data extraction
  • using box parser sucks
  • Add a SourceBuffer event please, sidx time offset
  • Safari does it for ID3 emsg data
• Other topics we didn't get to
  • Infinate GOP GC
  • Multi SourceBuffer
  • new SourceBuffer no tag

Talk: Eric @ Apple

• TextTrackCue constructor that takes document fragment (VTT markup?)
  • fragment can have inline styles
• Native rendering honors Apple accessibility subtitle styling preferences

Talk: MediaCapabilities updates

• HLS decode and display support
• Spacial Audio support

Low-Latency

• WebTransport

  • Reliable vs Unreliable data channel (ex: http vs udp)
  • Quic / WebSocket / UDP / WebRTC
  • Application can fallback to HTTP2 or Quic fallback on it's own
  • WebRTC is overkill for Client-Server data transfer (more for P2P)
  • Unreliable Quic provides congestion control not available with UDP alone

• Common Workflow

  • How to simultaneously publish
    • Dash-LL (CTE)
    • LHLS (CTE)
    • LL-HLS from Apple
      • Will: double egress, less cache efficiency
      • CDNs don't do range-requests for partial files
      • Browser cache doesn't support H/2 push range-requests
        • Link header is being reused which breaks other uses
        • Will: make a new header explicitly for this
      • Steve: Who will implement this spec?

• Bandwidth Estimation

  • ACTE doesn't work (for Twitch in browsers outside of Chrome)
  • Side load to get estimation
    • more packets in addition to current or another rendition?
  • A new API for getting bandwidth (server-client) from the browser
    • Will: extension to fetch API? kbps
    • NetworkInfo?
    • Performance Resource Timing?
  • BYO Readable Stream in fetch or set highwatermark
  • Measure bursts
    • but what about web developers who use dev tools to throttle and complain about player behavior
    • small chunks may always be offloaded and come bursts that look like higher throughput than what is available
    • H/2 cache ruins estimation
  • Hit up WHATWG for fetch extensions

• PlaybackRate adjustment

  • Pitch correction is not uniform

• WebRTC

  • Will: When will AV1 real-time be supported (Using "David" decoder)

Shaka Streamer

• Simply setup packaging for streaming without all the complexity involved in using FFMPEG
• widevine
• (Google) cloud push

Media-Internals

It's coming to Dev-Tools!

Error Handling

• Video decode errors (code 3)

• Microsoft extended error codes on media-errors

  • Two pages of DRM errors

• Chrome EME DRM errors

• Eric: Don't worry about what's possible or what the underlying errors are

  • Identify the type of information that would be useful and make a proposal

Additional Notes: https://docs.google.com/document/d/1BaxJtVFGFv9sLMT5UkM7g3KYo0OTOh54ptWQJ82qKNM/edit#heading=h.74gq3url0e1s (these are also available in FOMS http://www.foms-workshop.org/foms2019SF/pmwiki.php/Site/Schedule)

Cross-platform, interop

Interop issues

• HLS Manifest metadata: DATERANGE tags not exposed in Safari as "metadata" TextTrack cues
  • There's a patch coming to Safari Preview soon
  • Need to verify SCTE data in DATERANGE tags with matching ids does not cause MediaElement error
  • Need to verify cue time ranges when stream is missing PDT (even though streams with DATERANGE should require PROGRAM-DATE-TIME)
• MSE Buffer eviction is problematic on TVs
  • See new eviction policy proposal (in MSE v2)
• setLiveSeekableRange needed when using native controls. Appending on certain platforms with duration Infinity can fail
  • Which environments? Is there a bug filed for this?
• Libraries for testing support on TVs:
  • https://www.cobalt.dev/
  • https://github.com/cta-wave/WMAS
• EME crypto scheme detection
  • Coming soon
• fetch in workers is supported
  • Chrome yes
  • Firefox yes
  • Safari no
  • TVs no
  • Since client will need to support fetch inside and outside of the workers, should there be an example feature test for this?
  • What about libraries that accept network filters or loaders as input on the main thread?
• Only naive fullscreen on iOS
  • Prevent players from offering an auto-rotate to fullscreen in portrait orientation (as in Youtube app and active viewable players in Android Chrome)
• 360 video such a small use case but copying video context is still a huge challenge (WebGL, CORS)

Tuesday 10/22

Community

• How to improve attendence at local video-dev meetups
• How to improve FOMS
• How to make attendance more diverse

SCTE-35 Ad Breaks in Broadcast

• Ad break start: barter, opportunity start: ads

MediaCapabilities v2

• Hardware decoder or not?
  • powerEfficient bool indicates a hardware encoder or software decoding at small resolutions
  • powerEfficient will return true when there is a lack of data
• Multiple decoders?
  • No. Would be a hack and not reliable or useful in the context of a single page.
• EME discoverability?
  • Shaka doesn't yet use MediaCapabilities
  • It does have to pass video and audio capabilities "robustness" to EME to get a MediaKey ("robustness" used by Widevine will be deprecated)
• RemotePlayback API is a pain for AirPlay
  • How do you pick the right stream (url)? Requires out-of-band knowledge
  • When an Apple device specified a remote AirPlay device, that device handles playback of urls
    • canPlay may be wrong on the sender
    • If using WebAudio API then bytes are sent across
    • With MSE it's more complicated
  • Sender MediaElement would not dispatch an "error" event
  • Could maybe use the MediaElement Source element list
    • How does one specify a source element for use with MSE (blob)?
  • You can't change a url mid-stream, but could reload alternate SSAI'd stream urls
• CPU Info
  • CPU and GPU info is not necessarily helpful and not available for privacy reasons

FOMS is a wrap!

DEMUXED

Wednesday 10/23

NICK CHADWICK @MUX

Super Resolution: The scaler of tomorrow, here today!

RYAN B HARVEY

Modeling the conceptual structure of FFmpeg in JavaScript

SARAH ALLEN

RTMP: web video innovation or Web 1.0 hack… how did we get to now? Sarah worked at Macromedia and Adobe on Director and Flash

ZACHARY CAVA

Scalable Per-User Ad Insertion in Live OTT

• DASH manifests allow for "wrapped" ad manifest patches

CHARLES SONIGO & JEAN-BAPTISTE LOUAZEL @ STREAMROOT

Building an automated testing suite: How to gain confidence that your release will not break playback for any platform/player/OS/format combination (joint talk) https://github.com/streamroot/dna-integration-samples

Thursday 10/24

Marina Kalkanis, M2A Media: Apple Low-Latency HLS

Serving LL-HLS For DAZN Live Sporting Events

• Features:
  • Partial Segments
  • Playlist Blocking (until refreshed with msn/part query request)
  • Http/2 (Push part or segment with playlist msn/part query request)
  • Delta Playlist (SKIP request)
  • Rendition Report
• Latency comparison
  • Typical latency: ~6s segmenta x ~5 trips:
    • encoder, origin, cache , CDN, client buffer
  • LL latency: .23 x 5 = 1.6s
• You may have multiple parts for a single GOP
  • 8 parts with only 2 that are "INDEPENDENT=YES" (GOP key frames)
  • 1.9s GOP to align with audio sample rate (48hz?)
• Verify blocking, push, delta working properly
  • Use session ids to help with login
• Challenges
  • HTTP/2 support (works great, but not supported everywhere)
  • Players (Apple still changing spec)
  • DVR

BEN DODSON: Analyzing Video Metrics like Richard Feynman

Book: "What DO you care what other people think?"

• Don't fool yourself
• Even with high quantitative abilities, your biases limit your ability
• Look at the Anscombe's quartet different data with same sample variance, mean, etc... https://en.wikipedia.org/wiki/Anscombe%27s_quartet
• Which percentage of users experience a p90 stall duration?
• Have curiosity and a bit of luck (Ask if it's a valve.)

LIGHTNING TALKS

Check out the video-dev jokes session

TE-YUAN HUANG

QoE Impact from Router Buffer sizing and Active Queue Management

STEVE ROBERTSON

This talk is not really about JavaScript

• dropped frames are not really caused by network conditions. dropped frames happen when:
  • switching tabs
  • audio and video tracks are not perfectly aligned
  • other page/browser/os performance issues
• don't change from the ideal path just because of dropped frames

ASHUTOSH AGRAWAL

Doing Server-Side Ad Insertion on Live Sports for 25.3M Concurrent Users

WILL LAW

Three Roads to Low-Latency - DASH-LL - LHLS - Apple LL-HLS

• Many commonalities
• Differences
  • LL-HLS has no CTE support
  • Only LL-HLS descibes internal segment structure (INDEPENDENT=YES) TODO: Add image

Apple Low-Latency Discussion

Friday 10/25

Organizers: Will Law and Josh Tidsbury

Meeting minutes and agenda: https://docs.google.com/document/d/17Ckfq0mgZbD9T9UPyQ8Pk-envNXsVPZocLpKOYbA7as/

24 hour test stream https://ll-hls-test.apple.com/master.m3u8

Release Progress

• Low-latency HLS is still in Beta
• iOS 13.2 / macOS Catalina 10.15.1. Is a reasonable basis for testing
• Still tuning Apple clients and collecting feedback on spec
• Will (most likely) emerge from Beta in first half of 2020

Key optimizations come with pipelining (init) segments in order (request at all once)

• How do you measure throughput when pipelining? (Ignore individual requests and measure throughput end-to-end)

Twitch LL-HLS / LHLS of round-trip comparison and analysis: https://docs.google.com/document/d/1UVraLyvcbzrU0Ygf9e7DPx9t0rEDoWFn_q2xdxUc-A0/edit

ExoPlayer Low-latency live playback https://docs.google.com/document/d/1z9qwuP7ff9sf3DZboXnhEF9hzW3Ng5rfJVqlGn8N38k/

Appendix A: CDN Tune-In: Age header is required in the spec But, if there is no Age header consider the playlist to be up-to-date? That will not be true for all (types of) HLS playlist (or cdn/server responses) Could the reference tools (or will the reference stream) add am Age header How about making a second blocking request for the next part to get in sync Guidelines for pipelining parts up to the first push playlist/part request A blocking request returned from cache is not up-to-date

• the initial response could be as old as one target duration
• this means the first blocking request could still come from cache (and not be up-to-date)

Bad clients can create long-lasting negative responses if negative caching is not done correctly (or per spec)

LL-LHLS playlist: Can we have it both ways?

HLS-IF? Can we create an industry forum that will guide the development of the spec and have Apple adopt work based on common sense So far we have:

• DASH-IF
• CTA-WAVE
  • CMAF-IF
  • https://github.com/cta-wave/R4WG20-QoE-Metrics

TODO: HLS.js roadmap for Low-Latency HLS features. Could we roll out support in phases? (some of this would depend on server/CDN support of server control and parts)

• Server Control
  • block reload
  • can-skip delta playlists
  • hold-back
• Part Support
  • CDN Tune-in / playlist sync and part-holdback pipelining
  • byterange part requests
    • multi-part range requests?
• Rendition Report

Apple LL-HLS Workshop is a wrap!

Notes

• When do browsers start playback? Measure buffering length(s) at canplay across UAs
• Eric @ Apple has a patch for inband manifest DateRange metadata
• ArrayBufferBuffer spec (Iterable of ArrayBuffers that acts as a single ArrayBuffer to avoid concats/alloc)
• TODO: elbar@peer5.com Peer5: Access to (or interface for both) HLS.js Loader and pLoader, registerNetwork
  • shaka.net.NetworkingEngine.registerScheme(schemeId, requestCallback)
  • Using the loader allows them to provide bandwidth estimate
  • Provide a stable path even if undocumented for accessing hls.js and shaka
  • Must be global context so it applies to all players
• smart-TV resources
  • https://developer.samsung.com/tv/develop/specifications/web-engine-specifications
  • https://developer.samsung.com/tv/develop/specifications/media-specifications
  • https://developer.samsung.com/tv/develop/specifications/tv-model-groups