  One ABR algorithm implemented on Puffer is BOLA-BASIC, the simplest variant
of BOLA. BOLA finds wide use in industry, notably in the MPEG-DASH reference
player used as the basis for video players at Akamai, BBC, Orange, and CBS. The
overall goal of BOLA is to maximize each encoded chunk's video quality while
minimizing rebuffering. To measure video quality, Puffer uses the structural
similarity metric SSIM, whereas BOLA and other ABR algorithms like BBA, MPC,
and Pensieve are more commonly implemented using bitrate (or a variant of
bitrate).
  While bitrate is frequently used, BOLA allows the video provider to define
its own proxy of video quality as the algorithm's "utility" function. However,
using SSIM as utility proved surprisingly complex for BOLA-BASIC, despite the
algorithm's simplicity. Given the rising popularity of SSIM and related quality
metrics, we anticipate that a growing number of Puffer-like systems will face
similar challenges. We hope developers of such systems find our experiences
informative as they implement algorithms designed with bitrate-based utility in
mind.
