ffmpeg problem

I'm new to ffmpeg, and try to figure out how to use it.
- I have an hls stream, that I could download by using ffmpeg
- I need to download stream segment manually and then mux them using ffmpeg. But when I try to mux each segment manually, it causes following error:

[mov,mp4,m4a,3gp,3g2,mj2 @ 0x12f6f40] could not find corresponding track id 1
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x12f6f40] could not find corresponding trex
[mov,mp4,m4a,3gp,3g2,mj2 @ 0x12f6f40] error reading header
audio-1224.mp4: Invalid data found when processing input


Is there anyway to fix this problem?