HLS WWDC2020
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This document outlines improvements to low-latency HTTP Live Streaming (LL-HLS). It discusses adopting ad insertion, reducing latency through blocking playlist reloads, preload hints, playlist delta updates, and audio experience optimizations. LL-HLS aims to deliver content with minimal delay by simplifying delivery directives, generating CMAF formats, and preloading segments before playback is needed. Blocking playlist reloads allow clients to wait for new segments rather than polling frequently. Playlist delta updates send only changes to reduce bandwidth. These changes bring LL-HLS out of beta status.
HLS WWDC2020
- 2. Outline ● What’s new in Low-Latency HLS ● Adopt Ad Insertion to Low-Latency HLS ● Reduce Latency with HLS Blocking Playlist Reload ● Discover HLS Blocking Preload Hints ● Optimize Live Streams with HLS Playlist Delta Updates ● Improve stream authoring with HLS Tools ● Deliver a Better HLS Audio Experience
- 3. What’s New in Low-Latency HLS
- 8. Important changes ● Replaced HTTP/2 Push with Preloading Hinting ● Simplified Delivery Directives ● Generate CMAF in reference tools Everything is included in the current HLS spec Low-Latency HLS comes out of beta this year ● Aim to deliver your service
- 9. Quick Review of Regular Live HLS works
- 35. And it has to supply preload hints for both as well
- 37. What’s Blocking Playlist Reload? ● HLS clients discover new segments by reloading the Playlist
- 38. What’s Blocking Playlist Reload? ● HLS clients discover new segments by reloading the Playlist ● Original HLS approach (polling) delays discovery
- 39. What’s Blocking Playlist Reload? ● HLS clients discover new segments by reloading the Playlist ● Original HLS approach (polling) delays discovery ● Low-Latency HLS introduced server Delivery Directives
- 40. ● HLS clients discover new segments by reloading the Playlist ● Original HLS approach (polling) delays discovery ● Low-Latency HLS introduced server Delivery Directives ● Client asks server to hold reload request until new segment appear ● Response unblocks when Playlist updates What’s Blocking Playlist Reload?
- 63. Other exceptional cases ● _HLS_msn and _HLS_part are ignored if Playlists contains EXT-X-ENDLIST
- 64. Other exceptional cases ● _HLS_msn and _HLS_part are ignored if Playlists contains EXT-X-ENDLIST ● Server unblocks immediately if Playlist is newer than requested ● Requested segment/part is not the most recent ○ It might even have rolled out of the Playlist
- 65. ● _HLS_msn and _HLS_part are ignored if Playlists contains EXT-X-ENDLIST ● Server unblocks immediately if Playlist is newer than requested ● Requested segment/part is not the most recent ○ It might even have rolled out of the Playlist ● Server may time out if it spends too long blocked Other exceptional cases
- 79. Using CMAF Chunks with LL-HLS ● Each resource (URL) corresponds to a Parent Segment ● Each Parent Segment contains multiple CMAF Chunks ● Each CMAF Chunk is a Partial Segment ○ Specified as Parent Segment URL + byte-range
- 93. Extension Playlist Delta Update
- 100. Wrap up ● Provide Playlist Delta Updates for livestreams with large windows ● Latest OS offers v2 updates that include EXT-X-DATERANGE tags ● Improves Playlist reload performance, which increases reliability
- 115. SCORE attribute
- 118. Thank you!