[FFmpeg-user] Problem with lowering bit rate

[ywoon]

Hi,
I want to transcode a video strem to mulpiplt bitrates, I cant get the
appropriate bitrate using the following command, ffmpeg seems to ignore the
bit rate!

1) ffmpeg -y -i input -vcodec libx264 -vprofile main -preset ultrafast -b
50k -minrate 50k -maxrate 50k -bufsize 100k -f flv -vf scale=-1:480 -threads
0 -loglevel error -ar 44100 output1

  ffmpeg -i output1

ffmpeg version git-2012-10-31-dc239b3 Copyright (c) 2000-2012 the FFmpeg
developers
  built on Oct 31 2012 10:58:54 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
  configuration: --enable-gpl --enable-version3 --enable-nonfree
--enable-libvorbis --enable-libx264 --enable-x11grab --disable-yasm
  libavutil      52.  1.100 / 52.  1.100
  libavcodec     54. 70.100 / 54. 70.100
  libavformat    54. 35.100 / 54. 35.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 20.113 /  3. 20.113
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
Guessed Channel Layout for  Input Stream #0.1 : stereo
Input #0, flv, from 'output1':
  Metadata:
    encoder         : Lavf54.35.100
  Duration: 00:00:18.49, start: 0.000000, bitrate: 381 kb/s
    Stream #0:0: Video: h264 (Constrained Baseline), yuv420p, 600x480 [SAR
16:15 DAR 4:3], 50 kb/s, 25 tbr, 1k tbn, 50 tbc
    Stream #0:1: Audio: adpcm_swf, 44100 Hz, stereo, s16, 352 kb/s


2) ffmpeg -i input -vcodec libx264 -vprofile main -preset ultrafast -b 50k
-minrate 50k -maxrate 50k -bufsize 100k -f flv -threads 0 -loglevel error
-ar 44100 outut2.flv


  ffmpeg -i output2.flv

ffmpeg version git-2012-10-31-dc239b3 Copyright (c) 2000-2012 the FFmpeg
developers
  built on Oct 31 2012 10:58:54 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
  configuration: --enable-gpl --enable-version3 --enable-nonfree
--enable-libvorbis --enable-libx264 --enable-x11grab --disable-yasm
  libavutil      52.  1.100 / 52.  1.100
  libavcodec     54. 70.100 / 54. 70.100
  libavformat    54. 35.100 / 54. 35.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 20.113 /  3. 20.113
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
  libpostproc    52.  1.100 / 52.  1.100
Guessed Channel Layout for  Input Stream #0.1 : stereo
Input #0, flv, from ' output2.flv':
  Metadata:
    encoder         : Lavf54.35.100
  Duration: 00:00:16.69, start: 0.000000, bitrate: 340 kb/s
    Stream #0:0: Video: h264 (Constrained Baseline), yuv420p, 720x576 [SAR
16:15 DAR 4:3], 50 kb/s, 25 tbr, 1k tbn, 50 tbc
    Stream #0:1: Audio: adpcm_swf, 44100 Hz, stereo, s16, 352 kb/s

As you  see, I want the video bit rate to be 50, but its 300+, what's wrong?


Regards








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