Streaming • Multiple sources used to control bandwidth usage Optimized & Proxy Media • Efficient-to-edit (e.g., ALL-I) sources used to speed up editing at the cost of storage
Consider a video streaming service with a search engine that generates video compilations in response to searches • Many short segments need to be decoded quickly • Must use existing VOD/ABR sources from the CDN Which video source do you use? “Lowest bitrate 720p H.264 source”
lowest bitrate 720p H.264 source” • Crude enforcement of a quality constraint • Likely the fastest source to access, but not always! • Sometimes a higher bitrate/resolution source is faster to access if it has GOPs better aligned with the required segment • Sometimes jumping between multiple sources is faster
and a required segment range, find the most efficient access plan to decode the needed segment. “Use any/all sources, ensure VMAF > 85, minimize latency”
A1 F2 A1 F3 A1 B2 A1 B2 A1 B2 A1 F4 B2 B2 A1 B2 A1 B2 B2 A1 B2 B2 A2 Only five conditions when frame needs considering: • The frame before the start of the range • The last frame of the range • The frame prior to the start of a GOP • The start of a GOP • The end of a GOP All other frames are omitted when constructing the frame transition graph.
an atomic operation • MSSOpt uses per-GOP quality statistics • Using multiple sources results in scattered random I/O • However, this is considered by the optimizer via the cost heuristic 11
series • All sources downloaded from YouTube (via yt-dlp) • Encoded streams kept unmodified • Each video around 55 minutes @ 29.97 FPS • 256x144 to 1920x1080 • Average of 29.8 sources per video, almost all H.264 or VP8 Metric: • Comparing Multi-Source to optimal Single-Source decode latency 12
75 Quality (VMAF) Decode Time (s) Method Multi−Source Single−Source 13 As quality constraints are lowered decode time decreases Using multiple sources results in lower latency than using the optimal single source
2 5 10 15 30 60 Segment Length (s) Relative Decode Time (percent) Segment Length Decode Time MS ≠ SS Opt. Time 1s 98.8% 16.7% 1.00 ms 2s 98.0% 29.7% 1.19 ms 5s 94.9% 60.7% 1.38 ms 10s 90.9% 82.5% 1.59 ms 15s 87.8% 89.2% 1.73 ms 30s 83.1% 95.6% 2.03 ms 60s 76.8% 97.5% 2.97 ms Shorter decoded ranges saw less speedup as many were naturally single-source optimal MSSOpt executes in single-digit milliseconds
can use like proxy/optimized media for faster seeking Using multiple video sources simultaneously for video segment access has a better cost/quality tradeoff MSSOpt solves the generalized form of Multi-Source Selection 17