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1. Initial bitrate is configurable for 4k and non-4k, based on a desired target bitrate. The profile with smallest bitrate >= that target is picked. If target bitrate is higher than all available bitrates, top profile is picked.
   1. Current defaults:
   2. Initial bitrate: 2.5 mb - for non-4k playback
   3. Initial bitrate for 4K playback: 13mb ie, 3/4 profile

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1. As each fragment is downloaded, an estimated available bandwidth sample is computed and shared with ABR manager (total bytes / download time); configuration exists to exclude "too small" fragments from this sampling.

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1. ABR manager filters "old" estimated bandwidth samples, using average recent bandwidth samples for

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1. its estimated effective bandwidth (threshold = 5s).

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1. ABR manager will jump when detecting big swing in available bandwidth (allowing quick skip up/down over other profiles).

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1. ABR manager will more conservatively accommodate small shifts in available bandwidth (to avoid flipping up/down if we're on the edge); requiring multiple satisfying samples before ramping up/down in this case

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1. Upon initial tune, with healthy network, ramps to top profile will occur after playout of three fragments (typically 3*2s=6s) at initial profile

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1. A “useNewABR” is recently introduced, to use a hybrid buffering/throughput model.  This takes into account buffer health to avoid unnecessary rampdowns when buffer is healthy, along with a mechanism to escape "ABR valley" when buffers are healthy but throughput as measured appears poor.

Configuration/defaults:
abr-cache-life=<x in sec> lifetime value for abr cache for network bandwidth calculation(default 5 sec)
abr-cache-length=<x> length of abr cache for network bandwidth calculation (default 3)
abr-cache-outlier=<x in bytes> Outlier difference which will be ignored from network bandwidth calculation(default 5MB)
abr-nw-consistency=<x> Number of checks before profile incr/decr by 1.This is to avoid frequent profile switching with network change(default 2)
abr-skip-duration=<x> minimum duration of fragment to be downloaded before triggering abr (default 6 sec).

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with VBN build we can create/use /opt/aamp.cfg to force a specific profile.  The relevant configuration options are:abr       

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so for For example:

```abr

default-bitrate=1200000```

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