>ffmpeg -i bb.flv -vcodec copy -acodec copy -f mp4 bb.mp4
ffmpeg version 0.11.1 Copyright (c) 2000-2012 the FFmpeg developers
  built on Aug  7 2012 03:09:12 with gcc 4.6.2
  configuration: --pkg-config=pkg-config --prefix=/home/td/software/packages/win
32 --enable-memalign-hack --arch=x86 --target-os=mingw32 --cross-prefix=i686-w64
-mingw32- --enable-libmp3lame --enable-libx264 --enable-w32threads --disable-pth
reads --enable-gpl
  libavutil      51. 54.100 / 51. 54.100
  libavcodec     54. 23.100 / 54. 23.100
  libavformat    54.  6.100 / 54.  6.100
  libavdevice    54.  0.100 / 54.  0.100
  libavfilter     2. 77.100 /  2. 77.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0. 15.100 /  0. 15.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, flv, from 'bb.flv':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.3.100
  Duration: 00:04:36.26, start: 0.024000, bitrate: 536 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 1280x720, 398 kb/s, 30 tbr, 1k tbn
, 60 tbc
    Stream #0:1: Audio: mp3, 44100 Hz, stereo, s16, 128 kb/s
File 'bb.mp4' already exists. Overwrite ? [y/N] y
Output #0, mp4, to 'bb.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf54.6.100
    Stream #0:0: Video: h264 (![0][0][0] / 0x0021), yuv420p, 1280x720, q=2-31, 3
98 kb/s, 1k tbn, 1k tbc
    Stream #0:1: Audio: mp3 (i[0][0][0] / 0x0069), 44100 Hz, stereo, 128 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
frame= 8058 fps=0.0 q=-1.0 Lsize=   18122kB time=00:04:36.07 bitrate= 537.7kbits
/s
video:13445kB audio:4313kB global headers:0kB muxing overhead 2.044014%