Use o ffmpeg:
ffmpeg -i filename.flv
Procure:
Input #0, flv, from 'The Veronicas - Hook Me Up.flv':
Metadata:
starttime : 0
totalduration : 179
totaldatarate : 841
bytelength : 18910448
canseekontime : true
purl :
pmsg :
Duration: 00:02:59.39, start: 0.000000, bitrate: 843 kb/s
Stream #0:0: Video: h264 (Main), yuv420p,
640x480 [SAR 1:1 DAR 4:3], 726 kb/s, 23.98 tbr, 1k tbn, 47.95 tbc
Stream #0:1: Audio: aac, 44100 Hz, stereo, fltp, 128 kb/s