[FFmpeg-user] Option `-b' seems not to have any effect

[dE .]

On 12/02/11 19:17, Rodolfo Medina wrote:
> Hi to all ffmpeg users.
>
> Whatever value I put for `-b' (e.g.: -b 64k, -b 32k, -b 0k) the output file
> size remains always 26M.  Is that normal?  If not, how to fix that?  Below is
> ffmpeg's output, and many thanks indeed for any help supported.
>
> Rodolfo
>
>
> $ ffmpeg -i SDV_0597.MP4 -acodec copy -vcodec copy -t 46 -b 64k test.mp4
> FFmpeg version r11872+debian_0.svn20080206-17, Copyright (c) 2000-2008 Fabrice Bellard, et al.
>    configuration: --enable-gpl --enable-libfaad --enable-pp --enable-swscaler --enable-x11grab --prefix=/usr --enable-libgsm --enable-libtheora --enable-libvorbis --enable-pthreads --disable-strip --enable-libdc1394 --disable-armv5te --disable-armv6 --disable-altivec --disable-vis --enable-shared --disable-static
>    libavutil version: 49.6.0
>    libavcodec version: 51.50.0
>    libavformat version: 52.7.0
>    libavdevice version: 52.0.0
>    built on Feb 10 2009 08:13:56, gcc: 4.3.3
> Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'SDV_0597.MP4':
>    Duration: 00:09:36.2, start: 0.000000, bitrate: 5306 kb/s
>      Stream #0.0(eng): Video: h264, yuv420p, 720x576 [PAR 0:1 DAR 0:1], 25.00 tb(r)
>      Stream #0.1(eng): Audio: mpeg4aac, 44100 Hz, stereo
> Output #0, mp4, to 'test.mp4':
>      Stream #0.0(eng): Video: 0x0000, yuv420p, 720x576 [PAR 0:1 DAR 0:1], q=2-31, 25.00 tb(c)
>      Stream #0.1(eng): Audio: 0x0000, 44100 Hz, stereo
> Stream mapping:
>    Stream #0.0 ->  #0.0
>    Stream #0.1 ->  #0.1
> Press [q] to stop encoding
> frame= 1150 fps=  0 q=-1.0 Lsize=   26009kB time=46.0 bitrate=4631.8kbits/s
> video:25296kB audio:695kB global headers:0kB muxing overhead 0.069898%
>
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I may be wrong, but when you're copying a stream, encoding isn't 
involved, and when encoding isn't involved, you can't control the bitrate.