The commit r14491 on libavformat/aviobuf.c brakes the playing of several mp4/mov movies for me. In my case, mplayer enters an infinit loop in libavformat/mov.c:mov_read_udta(). Reverting r14491 fixes this problem. I guess that checking libavformat/aviobuf.c:url_fseek() return value would be a better approach, but it seems that lots of files are using this function without checking its return code.