something wrong in your programs

When I use it to parse a little big flv ,which is about 3MB,it can't response the duration.The data presented as follow:
FLV Version: 1
Duration : Second(s)
File Size: 3248957bytes
Width: 352 Pixel(s)
Height: Pixel(s)
Framerate: 0.00 FPS
Video Data Rate: 158 Kbps
Audio Data Rate: 0 Kbps
Audio Delay: Second(s)
Audio Codec ID: 2
Audio Format: MP3
Video Codec ID: 2
Video Format: Sorenson H.263
Header Size: 9 Byte(s)

Execution time: 0.000358 Microsecond(s)

Nothing is wrong, there is no meta data tag for duration and some other fields in your FLV. Meta data of FLV file is dependent upon the converter program.