Since my last post I have worked on applying a similar approach of making HTTP range requests to obtain indexes necessary for seeking in the Flash Video format version 1 (‘old’ FLV, if you will) and AVI (both legacy and ODML) in GStreamer.
Legacy AVI was fairly straightforward as we only need to do one seek to get the index. ODML AVI was somewhat messy because we had to perform multiple seeks as there can be multiple indexes spread across the file. As such, within the GStreamer framework, we have to handle the multiple seeks in the streaming thread rather than in the seek thread as we might prefer. This is because we cannot block the seek thread.
Check out the head commit of git master or the next release of GStreamer to try out this work. If you find bugs, file them on bugzilla as normal for GStreamer. 