Video data can be slow to process due to the size of video streams and the computational complexity needed to decode, transform, and encode them. These challenges are particularly significant in interactive applications, such as quickly generating compilation videos from a user search. We look at optimizing access to source video segments in multimedia systems where multiple separately encoded copies of video sources are available, such as proxy/optimized media in conventional non-linear video editors or VOD streams in content distribution networks. Rather than selecting a single source to use (e.g., "use the lowest-bitrate 720p source"), we specify a minimum visual quality (e.g., "use any frames with VMAF ≥ 85"). This quality constraint and the needed segment bounds are used to find the lowest-latency operations to decode a segment from multiple available sources with diverse bitrates, resolutions, and codecs. This uses higher-quality/slower-to-decode sources if the encoding is better aligned for the specific segment bounds, which can provide faster access than using just one lower-quality source. We provide a general solution to this Quality-Aware Multi-Source Selection problem with optimal computational complexity. We create a dataset using adaptive-bitrate streaming Video on Demand sources from YouTube's CDN. We evaluate our algorithm on simple segment decoding as well as embedded into a larger editing system---a declarative video editor. Our evaluation shows up to 23% lower latency access, depending on segment length, at identical visual quality levels.

Querying video data has become increasingly popular and useful. Video queries can be complex, ranging from retrieval tasks (“find me the top videos that have … ”), to analytics (“how many videos contained object X per day?”), to excerpting tasks (“highlight and zoom into scenes with object X near object Y”), or combinations thereof. Results for video queries are still typically shown as either relational data or a primitive collection of clickable thumbnails on a web page. Presenting query results in this form is an impedance mismatch with the video medium: they are cumbersome to skim through and are in a different modality and information density compared to the source data. We describe V2V, a system to efficiently synthesize video results for video queries. V2V returns a fully-edited video, allowing the user to consume results in the same manner as the source videos. A key challenge is that synthesizing video results from a collection of videos is computationally intensive, especially within interactive query response times. To address this, V2V features a grammar to express video transformations in a declarative manner and a heuristic optimizer that improves the efficiency of V2V processing in a manner similar to how databases execute relational queries. Experiments show that our V2V optimizer enables video synthesis to run 3x faster.