Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for requesting potentially missing fragments in a media stream index are described in this specification. In one aspect, a method includes receiving a fragmented media stream index at a client system, where the media stream index includes a list of sequentially arranged fragment identifiers. Fragments listed in the media stream index can be requested from a server system. Fragment identifiers that are potentially missing in the media stream index can be identified based, at least in part, on a determined naming convention indicating the sequential arrangement of the fragment identifiers. Fragments can be requested based on the potentially missing fragment identifiers and processed for display when received.