Blind users interact with smartphone applications using a screen reader, an assistive technology that enables them to navigate and listen to application content using touch gestures. Since blind users rely on screen reader audio, interacting with online videos can be challenging due to the screen reader audio interfering with the video sounds. Existing solutions to address this interference problem are predominantly designed for desktop scenarios, where special keyboard or mouse actions are supported to facilitate 'silent' and direct access to various video controls such as play, pause, and progress bar. As these solutions are not transferable to smartphones, suitable alternatives are desired. In this regard, we explore the potential of motion gestures in smartphones as an effective and convenient method for blind screen reader users to interact with online videos. Specifically, we designed and developed YouTilt, an Android application that enables screen reader users to exploit an assortment of motion gestures to access and manipulate various video controls. We then conducted a user study with 10 blind participants to investigate whether blind users can leverage YouTilt to properly execute motion gestures for video-interaction tasks while simultaneously listening to video sounds. Analysis of the study data showed a significant improvement in usability by as much as 43.3% (avg.) with YouTilt compared to that with default screen reader, and overall a positive attitude and acceptance towards motion gesture-based video interaction.