Overview of Adaptive Bitrate Algorithms and ABR Design for Video Streaming
This content provides insights into the Adaptive Bitrate Algorithms (AAMP) and ABR Design, focusing on behaviors, throughput considerations, network consistency, profile selection, buffering strategies, and hybrid approaches. It covers topics such as segment downloading, network throughput estimation, profile switching, and buffer management in video streaming applications.
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AAMP Adaptive Bitrate Algorithms Overview of AAMP ABR Behavior
ABR Design - Throughput Retry download on timeout Default Settings: abr-cache-length = 3 abr-cache-life = 5 sec abr-cache-outlier = 5 Mbps aamp-abr-threshold-size= 6000 Segment Downloader Video/Audio/Iframe Segments Video Segment Size (bytes) > aamp-abr- threshold-size Successful Download Update Persisted Recent Download Statistics Downloaded bytes / time GetNetworkThroughput Bitrate Data Store of size = abrCacheLength (history cache size) Downloaded bytes / time Read download info < abr-cache-life Downloaded bytes / time Network throughput estimation; smoothing heuristic: Ignore outliers bps ( > abr-cache-outlier) Comcast Confidential & Proprietary Comcast Confidential & Proprietary 2
ABR Design - Throughput ABR check - after each segment download GetNetworkThroughput Default Settings: abr-skip-duration = 6 (2sec * 3 segs) abr-nw-consistency = 2 Read throughput Nw Total Dnld duration > abr- skip-duration* throughput < Profile BW No Yes Yes New Profile Selection based on NW BW Is new profile consistent (abrNwConsistency thrashing avoidance when on edge) Apply New Profile Note: *abr-skip-duration interval prevents profile switching immediately after 1st segment download during tune. * consistency count set to 1 during first profile switch after tune to reduce additional segment download time for profile change . Comcast Confidential & Proprietary Comcast Confidential & Proprietary 3
Hybrid ABR ( Throughput + Buffer) Default Settings: max-buffer-rampup= 15sec Minimum buffer = 1 fragment duration + NetworkDownload Timeout(10sec) Profile Selection based on NW BW No Profile Changed ? ABR Valley escape heuristic Yes No change in profile for some duration . New Profile > Current Profile ? Yes Check for enough buffer before rampup (max-buffer-rampup) .If not switch to previous profile If one profile download and if *minimum buffer available ,then not to switch profile. Buffer < min buffer ? Buffer > max buffer ? Select Next Lower profile Select Next Higher profile Apply New Profile Comcast Confidential & Proprietary Comcast Confidential & Proprietary 4
Hybrid ABR ( Throughput + Buffer) Variable Timeouts Download timeouts are configured for a fixed/App configured timeout value ( Default of 10sec) With Hybrid ABR , timeout interval will be changed based on the buffer value available If video playback buffer > MaxBuffer Configured , then increase the timeout value . If video playback buffer < MaxBuffer Configured , then set the timeout to Fixed/App configured timeout interval Increased download timeout interval prevents frequent ABR rampdown , due to download delays . If download bps < profile bps && download time < fragment duration , then download bps = profile bps . This also keeps ABR steady . Comcast Confidential & Proprietary Comcast Confidential & Proprietary 5
