The primary objective of adaptive bitrate (ABR) streaming is to enhance users' quality of experience (QoE) by dynamically adjusting the video bitrate in response to changing network conditions. However, users often find frequent bitrate switching frustrating due to the resulting inconsistency in visual quality over time, especially during live streaming when buffer lengths are short. In this paper, we propose a practical smoothness optimized dynamic adaptive (SODA) controller that specifically addresses this problem while remaining deployable. SODA is backed by theoretical guarantees and has shown superior performance in empirical evaluations. Specifically, our numerical simulations show a 9.55% to 27.8% QoE improvement and our prototype evaluation shows a 30.4% QoE improvement compared to the state-of-the-art baselines. In order to be widely deployable, SODA performs bitrate horizon planning in polynomial time compared to brute force approaches that suffer from exponential complexity. To demonstrate its real-world practicality, we deployed SODA on a wide range of devices within the production network of Amazon Prime Video. Production experiments show that SODA reduced bitrate switching by up to 88.8% and increased average stream viewing duration by up to 5.91% compared to a fine-tuned production baseline.

The popularity of video streaming on smartphones has led to rising demands for high-quality mobile video streaming. Consequently, we are observing growing support for higher resolution videos (e.g., HD, FHD, QHD) and higher video frame rates (e.g., 48 FPS, 60 FPS). However, supporting high-quality video streaming on smartphones introduces new challenges---besides the available network capacity, the smartphone itself can become a bottleneck due to resource constraints, such as low available memory. In this paper, we conduct an in-depth investigation of memory usage on smartphones and its impacts on mobile video streaming. Our investigation - driven by a combination of a user study, user survey, and experiments on real smartphones - reveals that (i) most smartphones observe memory pressure (i.e., low available memory scenarios), (ii) memory pressure can have a significant impact on mobile video QoE when streaming high-quality videos, e.g., resulting in the mean frame drop rate of 9--100% across smartphones and significantly lower user ratings, and (iii) the drop in mobile video QoE happens primarily due to the way in which video processes interact with kernel-level memory management mechanism, with opportunities for improving mobile video QoE through better adaptation by video clients.

Video dominates Internet traffic today. Users retrieve on-demand video from Content Delivery Networks (CDNs) which cache video chunks at front-ends. In this paper, we describe AViC, a caching algorithm that leverages properties of video delivery, such as request predictability and the presence of highly unpopular chunks. AViC's eviction policy exploits request predictability to estimate a chunk's future request time and evict the chunk with the furthest future request time. Its admission control policy uses a classifier to predict singletons --- chunks evicted before a second reference. Using real world CDN traces from a commercial video service, we show that AViC outperforms a range of algorithm including LRU, GDSF, AdaptSize and LHD. In particular LRU requires up to 3.5× the cache size to match AViC's performance. Further, AViC has low time complexity and has memory complexity comparable to GDSF.

Most content providers are interested in providing good video delivery QoE for all users, not just on average. State-of-the-art ABR algorithms like BOLA and MPC rely on parameters that are sensitive to network conditions, so may perform poorly for some users and/or videos. In this paper, we propose a technique called Oboe to auto-tune these parameters to different network conditions. Oboe pre-computes, for a given ABR algorithm, the best possible parameters for different network conditions, then dynamically adapts the parameters at run-time for the current network conditions. Using testbed experiments, we show that Oboe significantly improves BOLA, MPC, and a commercially deployed ABR. Oboe also betters a recently proposed reinforcement learning based ABR, Pensieve, by 24% on average on a composite QoE metric, in part because it is able to better specialize ABR behavior across different network states.

The ever increasing quantity of user generated photos, nearly all compressed using JPEG, has created a growing storage burden on photo storage and sharing services. This creates the need for compression techniques that take JPEG compressed images as inputs. In this paper we propose two novel very low complexity codecs, ROMP and L-ROMP to recompress JPEG photos, achieving increased coding efficiency by making use of very large entropy coding tables. ROMP is a lossless JPEG recompression codec that achieves 15% average gains over JPEG, while L-ROMP is a lossy codec that can achieve 29% average compression gains over JPEG, by applying coefficient thresholding based on a perceptual criterion to a JPEG image before using the entropy coding of ROMP.

A fundamental problem in 802.11 wireless networks is to accurately determine the cause of packet losses. This becomes increasingly important as wireless data rates scale to Gbps, where lack of loss differentiation leads to higher loss in throughput. Recent and upcoming high-speed WLAN standards, such as 802.11n and 802.11ac, use frame aggregation and block acknowledgements for achieving efficient communication. This paper presents BLMon, a framework for loss differentiation, that uses loss patterns within aggregate frames and aggregate frame retries to achieve accurate and low overhead loss differentiation. Towards this end, we carry out a detailed measurement study on a real testbed to ascertain the differences in loss patterns due to noise, collisions, and hidden nodes. We then devise metrics to quantitatively capture these differences. Finally, we design BLMon, which collectively uses these metrics to infer the cause of loss without requiring any out-of-band communication, protocol changes, or customized hardware support. BLMon can be readily deployed on commodity devices using only driver-level changes at the sender-side. We implement BLMon in the ath9k driver and using real testbed experiments, show that it can provide up to 5× improvement in throughput.

Running a multimedia application such as audio playback or video playback on a mobile handheld device is a power hungry task. Mobile devices in question here may include smart phones, palmtops or ipods. As the battery time is limited on these platforms, complexity cutting and power saving is a critical issue and optimization of such power intensive tasks is inevitable. This paper outlines two complexity scalable approaches for video decoding on embedded platforms.