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• bash variable changes in loop with ffmpeg

  17 septembre 2018, par Mike

  I wrote a skript to quickly create short preview clips from vides I recorded on timestamps that I found worth checking out later for cutting.
  My file with the timestamps is written like this

  FILE_NAME1#MM:SS MM:SS
  
  FILE_NAME2#MM:SS MM:SS MM:SS MM:SS

  example :

  MAH01728#02:47 03:34 03:44 05:00 06:08 06:55

  The script looks like this :

  #!/bin/bash
  
  while read f
  
   do
  
  
  
   file=$(echo $f | cut -d"#" -f1)
  
   filename=${file}".MP4"
  
   timestamps=$(echo $f | cut -d"#" -f2)
  
  
  
  for time in $timestamps 
  
   do 
  
    ffmpeg -ss 00:${time}.0 -i "orig/${filename}" -c copy -t 10 "preview/${file}_${time}.MP4"
  
   done
  
  done < $1

  The script gets half of the previews that I want and on the other the filename is messed up and ffmpeg complains that the file is not found :

  orig/714.MP4: No such file or directory
  
  orig/00:58 01:25.MP4: No such file or directory

  So I modified the script for trouble shooting and just put an echo in front of the ffmpeg command - now all file names are correct. What am I missing ?

  ffmpeg -ss 00:01:47.0 -i orig/MAH01714.MP4 -c copy -t 10 preview/MAH01714_01:47.MP4
  
  ffmpeg -ss 00:02:00.0 -i orig/MAH01713.MP4 -c copy -t 10 preview/MAH01713_02:00.MP4
  
  ffmpeg -ss 00:00:58.0 -i orig/MAH01712.MP4 -c copy -t 10 preview/MAH01712_00:58.MP4
  
  ffmpeg -ss 00:01:25.0 -i orig/MAH01712.MP4 -c copy -t 10 preview/MAH01712_01:25.MP4

• How to decode mp3 to pcm by ffmpeg

  30 janvier 2017, par Meph-

  I need decode mp3 audio data to pcm. I have data which starts with mp3 header. Api-example.c doesn’t work, output is strange :

  

  command ffmpeg -i input.mp3 output.wav
  is great, this is what i need. But I cant find way how to do that in code. Does anybody know, where some tutorial with ffmpeg library is ? Thanks

  Edit 2.7.13 :

  Hi again,
  I rebuilt the audio decode example method from ffmpeg and my problem is probably here :

  len = avcodec_decode_audio4(avCodecContext,avFrame, &got_frame,&avPacket);    
  
  int data_size = av_samples_get_buffer_size(NULL,avFrame->channels,avFrame->nb_samples,AV_SAMPLE_FMT_S16P,1);

  data_size is size of data frame from decoder, it depends on number of channels, number of data samples and data type(my data are 16bit PCM stereo encoded to mp3 to 1152 samples of mp3 frame)

  If I open an output file in audacity, correct parameters, which give correct output, are stereo (right), 8bit pcm (wrong) and half sample rate (also wrong), what’s it happened ?

  data before encoding :
  16bit PCM 44100Hz, stereo

  data after decoding :
  8bit PCM 22050Hz, stereo ---> ???!!!

  I’m tired of this....

• arm : vp9 : Add NEON optimizations of VP9 MC functions

  3 novembre 2016, par Martin Storsjö

  arm : vp9 : Add NEON optimizations of VP9 MC functions
  This work is sponsored by, and copyright, Google.
  The filter coefficients are signed values, where the product of the
  
  multiplication with one individual filter coefficient doesn’t
  
  overflow a 16 bit signed value (the largest filter coefficient is
  
  127). But when the products are accumulated, the resulting sum can
  
  overflow the 16 bit signed range. Instead of accumulating in 32 bit,
  
  we accumulate the largest product (either index 3 or 4) last with a
  
  saturated addition.
  (The VP8 MC asm does something similar, but slightly simpler, by
  
  accumulating each half of the filter separately. In the VP9 MC
  
  filters, each half of the filter can also overflow though, so the
  
  largest component has to be handled individually.)
  Examples of relative speedup compared to the C version, from checkasm :
  
                         Cortex      A7     A8     A9    A53
  
  vp9_avg4_neon :                   1.71   1.15   1.42   1.49
  
  vp9_avg8_neon :                   2.51   3.63   3.14   2.58
  
  vp9_avg16_neon :                  2.95   6.76   3.01   2.84
  
  vp9_avg32_neon :                  3.29   6.64   2.85   3.00
  
  vp9_avg64_neon :                  3.47   6.67   3.14   2.80
  
  vp9_avg_8tap_smooth_4h_neon :     3.22   4.73   2.76   4.67
  
  vp9_avg_8tap_smooth_4hv_neon :    3.67   4.76   3.28   4.71
  
  vp9_avg_8tap_smooth_4v_neon :     5.52   7.60   4.60   6.31
  
  vp9_avg_8tap_smooth_8h_neon :     6.22   9.04   5.12   9.32
  
  vp9_avg_8tap_smooth_8hv_neon :    6.38   8.21   5.72   8.17
  
  vp9_avg_8tap_smooth_8v_neon :     9.22  12.66   8.15  11.10
  
  vp9_avg_8tap_smooth_64h_neon :    7.02  10.23   5.54  11.58
  
  vp9_avg_8tap_smooth_64hv_neon :   6.76   9.46   5.93   9.40
  
  vp9_avg_8tap_smooth_64v_neon :   10.76  14.13   9.46  13.37
  
  vp9_put4_neon :                   1.11   1.47   1.00   1.21
  
  vp9_put8_neon :                   1.23   2.17   1.94   1.48
  
  vp9_put16_neon :                  1.63   4.02   1.73   1.97
  
  vp9_put32_neon :                  1.56   4.92   2.00   1.96
  
  vp9_put64_neon :                  2.10   5.28   2.03   2.35
  
  vp9_put_8tap_smooth_4h_neon :     3.11   4.35   2.63   4.35
  
  vp9_put_8tap_smooth_4hv_neon :    3.67   4.69   3.25   4.71
  
  vp9_put_8tap_smooth_4v_neon :     5.45   7.27   4.49   6.52
  
  vp9_put_8tap_smooth_8h_neon :     5.97   8.18   4.81   8.56
  
  vp9_put_8tap_smooth_8hv_neon :    6.39   7.90   5.64   8.15
  
  vp9_put_8tap_smooth_8v_neon :     9.03  11.84   8.07  11.51
  
  vp9_put_8tap_smooth_64h_neon :    6.78   9.48   4.88  10.89
  
  vp9_put_8tap_smooth_64hv_neon :   6.99   8.87   5.94   9.56
  
  vp9_put_8tap_smooth_64v_neon :   10.69  13.30   9.43  14.34
  For the larger 8tap filters, the speedup vs C code is around 5-14x.
  This is significantly faster than libvpx’s implementation of the same
  
  functions, at least when comparing the put_8tap_smooth_64 functions
  
  (compared to vpx_convolve8_horiz_neon and vpx_convolve8_vert_neon from
  
  libvpx).
  Absolute runtimes from checkasm :
  
                            Cortex      A7        A8        A9       A53
  
  vp9_put_8tap_smooth_64h_neon :    20150.3   14489.4   19733.6   10863.7
  
  libvpx vpx_convolve8_horiz_neon : 52623.3   19736.4   21907.7   25027.7
  vp9_put_8tap_smooth_64v_neon :    14455.0   12303.9   13746.4    9628.9
  
  libvpx vpx_convolve8_vert_neon :  42090.0   17706.2   17659.9   16941.2
  Thus, on the A9, the horizontal filter is only marginally faster than
  
  libvpx, while our version is significantly faster on the other cores,
  
  and the vertical filter is significantly faster on all cores. The
  
  difference is especially large on the A7.
  The libvpx implementation does the accumulation in 32 bit, which
  
  probably explains most of the differences.
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavcodec/arm/Makefile
  • [DBH] libavcodec/arm/vp9dsp_init_arm.c
  • [DBH] libavcodec/arm/vp9mc_neon.S
  • [DBH] libavcodec/vp9.h
  • [DBH] libavcodec/vp9block.c
  • [DBH] libavcodec/vp9dsp.c