Google patents voice search system that prioritizes real human speech

1. A method comprising: receiving, at data processing hardware of a query processing backend, an automated speech recognition (ASR) request from a user device, the ASR request comprising: a speech input captured by the user device that includes a voice query; and content metadata associated with the speech input, the content metadata collected from two or more of a plurality of sources and generated by the user device, the content metadata indicating a likelihood that the corresponding ASR request corresponds to speech output from a real user in proximity to the user device instead of broadcast speech spoken by a human but that emanates from a non-human source; determining, by the data processing hardware, a priority score for the ASR request based on the content metadata associated with the speech input; caching, by the data processing hardware, the ASR request in a pre-processing backlog of pending ASR requests each having a corresponding priority score, the pending ASR requests in the pre-processing backlog ranked in order of the priority scores; in response to caching one or more new ASR requests in the pre-processing backlog of pending ASR requests, re-ranking, by the data processing hardware, all of the pending ASR requests in the pre-processing backlog in order of the priority scores; providing, by the data processing hardware from the pre-processing backlog, one or more of the pending ASR requests to a backend-side ASR module based on processing availability of the backend-side ASR module, wherein pending ASR requests associated with higher priority scores are processed by the backend-side ASR module before pending ASR requests associated with lower priority scores; and transmitting, from the data processing hardware, on-device processing instructions to the user device, the on-device processing instructions instructing the user device to transcribe at least a portion of any new speech inputs captured by the user device using a local ASR module residing on the user device when the user device determines the query processing backend is overloaded.