Performance of Low-Latency DASH/CMAF and Low-Latency HLS Systems
Reducing end-to-end streaming latency is critical for HTTP-based live video streaming. There are currently two new technologies in this domain: Low-Latency HTTP Live Streaming (LL-HLS) and Low-Latency Dynamic Adaptive Streaming over HTTP (LL-DASH). Several streaming players (Apple’s AVPlayer, Google’s Shaka Player, HLS.js, DASH.js, etc.), streaming encoding and packaging tools (Apple’s HTTP Live Streaming Tools, FFmpeg, GPAC, etc.), have recently added support for these formats. There are also several live LL-HLS and LL-DASH reference/demo streams available, showcasing the capabilities of these technologies and helping the implementation community to adopt them. However, how well such systems perform in real-world deployment scenarios is not well known. Specifically, not much is known about the performance of such low-latency systems in delivery to mobile devices, connected over rapidly changing and often highly loaded wireless cellular networks. In this talk, I will review some results obtained in this direction by the Brightcove Research team. Our study consists of a series of live LL-HLS and LL-DASH streaming experiments. For each experiment, we use the same video content, encoder, encoding profiles, and identical network conditions emulated by running traces of the existing cellular networks (Verizon 4G LTE, T-Mobile 4G LTE, etc.). Several key performance metrics are captured and reported in each experiment. We measure the average streaming bitrate, the overall amounts of media data downloaded, the intensity of data requests, streaming latency, playback speed variations, buffering, stream switching statistics, etc. These results are subsequently analyzed and used to characterize some typical limits of LL-HLS and LL-DASH-based systems and differences between them.