Efficient multi-bitrate HEVC encoding for adaptive streaming

Adaptive bitrate streaming is a critical feature in internet video that significantly improves the viewer experience by customizing video stream quality to the viewer device's capability and connectivity. Encoding the source content at multiple quality tiers or bitrates is extremely demanding for post-production houses, studios, and content delivery networks. This paper describes an intelligent multi-bitrate encoder, based on the High Efficiency Video Coding (HEVC)/H.265 standard that encodes a single title to multiple bitrates at significant performance gains and no compression efficiency loss, as compared to standalone single bitrate encoder instances. We first describe the threading infrastructure of x265, and demonstrate its ability to dynamically adapt to varying degrees of parallelism in hardware. We then describe the key architectural design of a multi-bitrate encoder, including thread synchronization challenges across encoder instances. We also discuss the analysis data shared across different quality tiers, that is carefully chosen to eliminate loss of compression efficiency compared to a single bitrate encoder instance. Finally, we show the high performance gains achieved by the multi-encoder, and demonstrate the feasibility of simultaneous encoding to multiple bitrates with negligible loss of compression efficiency.