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• How do I get audio files of a specific file size ?

  13 février 2016, par Houseman

  Is there any way to use ffmpeg to accurately break audio files into smaller files of a specific file size, or pull a specific number of samples from a file ?

  I’m working with a speech-to-text API that needs audio chunks in exactly 160,000 bytes, or 80,000 16-bit samples.

  I have a video stream, and I have an ffmpeg command to extract audio from it :

  ffmpeg -i "rtmp://MyFMSWorkspace/ingest/test/mp4:test_1000 live=1" -ar 16000 -f segment -segment_time 10 out%04d.wav

  So now I have 10 second audio chunks with a sample rate of 16 kHz. Is there any way to break this into exactly 160kb, 5 second files using ffmpeg ?

  I tried this :

  ffmpeg -t 00:00:05.00 -i out0000.wav outCropped.wav

  But the output was this :

  Input #0, wav, from 'out0000.wav':
  
    Metadata:
  
      encoder         : Lavf56.40.101
  
    Duration: 00:00:10.00, bitrate: 256 kb/s
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, 1 channels, s16, 256 kb/s
  
  Output #0, wav, to 'outCropped.wav':
  
    Metadata:
  
      ISFT            : Lavf56.40.101
  
      Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
  
      Metadata:
  
        encoder         : Lavc56.60.100 pcm_s16le
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
  
  Press [q] to stop, [?] for help
  
  size=     156kB time=00:00:05.00 bitrate= 256.1kbits/s

  but now the size is 156kb

  EDIT :

  My finished command is :

  ffmpeg -i "url" -map 0:1 -af aresample=16000,asetnsamples=16000 -f segment -segment_time 5 -segment_format sw out%04d.sw

• What does the fps mean in the ffmpeg output ?

  1er mars 2015, par jabal

  I am streaming a static png file with ffmpeg and it uses basically all my CPU. It seems a bit greedy to me, and even though I limited the fps on the input and output size, I am seeing a huge fps printed out.

  w:\ffmpeg\bin>ffmpeg.exe -loop 1 -framerate 1 -i w:\colorbar2.png -r 10 -vcodec libx264 -pix_fmt yuv420p -r 10 -f mpegts udp://127.0.0.1:10001?pkt_size=1316
  
  ffmpeg version N-68778-g5c7227b Copyright (c) 2000-2014 the FFmpeg developers
  
    built on Dec 29 2014 22:12:54 with gcc 4.9.2 (GCC)
  
  
  
  Input #0, png_pipe, from 'w:\colorbar2.png':
  
    Duration: N/A, bitrate: N/A
  
      Stream #0:0: Video: png, pal8, 320x240 [SAR 3779:3779 DAR 4:3], 1 fps, 1 tbr, 1 tbn, 1 tbc
  
  [libx264 @ 00000000002fb320] using SAR=1/1
  
  [libx264 @ 00000000002fb320] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
  
  [libx264 @ 00000000002fb320] profile High, level 1.2
  
  Output #0, mpegts, to 'udp://127.0.0.1:10001?pkt_size=1316':
  
    Metadata:
  
      encoder         : Lavf56.16.102
  
      Stream #0:0: Video: h264 (libx264), yuv420p, 320x240 [SAR 1:1 DAR 4:3], q=-1--1, 10 fps, 90k tbn, 10 tbc
  
      Metadata:
  
        encoder         : Lavc56.19.100 libx264
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  frame=561310 fps=579 q=25.0 size=  144960kB time=15:35:25.80 bitrate=  21.2kbits/s dup=505179 drop=0

  As you can see the frame counter goes up quickly and fps=579 is reported on the last line. I am confused now, what does that fps mean, if above the low frame per secs are also mentioned (output 10fps, input 1 fps)

  What am I doing wrong and how could I reduce CPU load more given that it’s a static file that is being streamed.

  Thanks !

• ffmpeg : Computing PSNR on RGB channels

  21 janvier 2016, par Mike

  I have 2 rgb48le tif images that I want to compare with ffmpeg to compute the PSNR

  ffmpeg automatically computes the PSNR on YUV channels instead of RGB.
  This is the command that I’m using on "ffmpeg-20160119-git-cc83177-win64-static" :

  ffmpeg -y -an -i image1.tif -i image2.tif -filter_complex "psnr" output.tif

  and this is the output :

  [tiff_pipe @ 045b36a0] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
  Input #0, tiff_pipe, from 'image1.tif':
  
    Duration: N/A, bitrate: N/A
  
  Stream #0:0: Video: tiff, rgb48le, 7680x4320 [SAR 1:1 DAR 16:9], 25 tbr, 25 tbn, 25 tbc
  
  [tiff_pipe @ 045c53a0] Stream #0: not enough frames to estimate rate; consider increasing probesize
  
  Input #1, tiff_pipe, from 'image2.tif':
  
    Duration: N/A, bitrate: N/A
  
      Stream #1:0: Video: tiff, rgb48le, 7680x4320 [SAR 1:1 DAR 16:9], 25 tbr, 25 tbn, 25 tbc
  
  Output #0, image2, to 'output.tif':
  
    Metadata:
  
  encoder         : Lavf56.40.101
  
  Stream #0:0: Video: tiff, rgb48le, 7680x4320 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc (default)
  
  Metadata:
  
    encoder         : Lavc56.60.100 tiff
  
  Stream mapping:
  
    Stream #0:0 (tiff) -> psnr:main
  
    Stream #1:0 (tiff) -> psnr:reference
  
    psnr -> Stream #0:0 (tiff)
  
  Press [q] to stop, [?] for help
  
  frame=    1 fps=0.3 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
  
  video:195568kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
  
  [Parsed_psnr_0 @ 045cf760] PSNR y:46.00 u:49.32 v:50.34 average:48.14 min:48.14 max:48.14

  Is this normal ?
  Is there a way to force the PSNR to compute on RGB48 each channel ?