Streaming videos in multiple-bitrates without manually creating video files in each b

I want to have a media file that I can stream at multiple bitrates using FFMPEG (for encoding and multiple bitrate generation) and Flash Media Server (for streaming). 

In "LIVE BROADCASTING" ffmpeg made multiple bitrate videos from a single bitrate source but there were no files for the different bitrates. A file would be created for different bitrates when a viewer requested that bitrate streaming video but when a request was terminated the generated file was deleted.

So I searched in Flash Media Server and found (hds-vod), but in hds-vod I should create one file for every bitrate, for example if I have 2000 videos in my archive with HD quality (1024 kbps) I should make 4 videos with different bitrates from one video and together I have created 10,000 videos.

So to have 2000 videos in five bitrates (1024k, 760k, 320k, 145k, 64k), and now I have 10,000 videos. I have space for 2000 videos and I don't have free space in my server for 10,000 video files.

I want to stream "ON-DEMAND" videos in my server and not have the different bitrate files be continually generated like this.

Does anyone have any advice?

Thank you