Lack of downloading progress causes erratic playhead behaviour.
With natively supported codecs – when viewing the file in a web browser, QuickTime knows the length of the file before it has loaded. Even when incomplete, the end of the timeline corresponds to the end of the full-length media. The timeline is also shaded to show what proportion of the file has loaded, and the playhead will not move beyond this point.
When playing Ogg media like this. This progress bar feature does not work, the entire bar is shaded as soon as the player appears. The end of the timeline also currently corresponds to the end of the downloaded portion of media, meaning that when playing & downloading at the same time, the playhead will reach the end and then start to move erratically backwards and forwards as downloading continues.