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• avformat/cache : Avoid int-overflow in cache compare function

  9 novembre 2015, par Bryan Huh

  avformat/cache : Avoid int-overflow in cache compare function
  cache protocol indexes its cache using AVTreeNodes which require a cmp
  
  function for inserting and searching new cache-entries. This cmp
  
  function expects a 32-bit int return value (negative, zero, or positive)
  
  but the cache cmp function returns an int64_t which can overflow the
  
  int, giving negative numbers for when it should be positive, vice versa.
  
  This manifests itself only for very large files (e.g. 4GB+)
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/cache.c

• Get decibel array from audiofile

  16 avril 2020, par R. Adang

  I am creating a React Native app and want to show list of decibel numbers based on an audio file.
so the goal is -> input : audiofile(mp3,wav etc) output : array of decibels for samples with X milliseconds. I know about FFMPEG, but I do not know how to use it to get the array. I see there is a waveform option, but this returns a png instead of the volume data.

  


• ffmpeg : how to correctly program input framerate calculation, given desired video length duration and output framerate ?

  19 septembre 2015, par user89

  Let us say that I have n pictures named as imgXY.png (where XY represent the numbers 0 to n-1, properly padded with zeros).

  From these, I would like to create a video that is t seconds long, that has an (output) framerate R.

  I want to figure out what the input framerate should be, so I do the following calculation :

  • time spent per frame : t_per_frame = t/n

  • input framerate : 1/t_per_frame = n/t

  However, when I then try to create a movie using the following command :

  ffmpeg -framerate n/t -i img%02d.png -r 30 test_output.mp4

  I don’t get a movie that is t seconds long, and only two of the frames end up getting displayed. Why is this the case ?

  The following questions were unhelpful :

  How to successfully use ffmpeg to convert images into videos

  Turning images into videos with ffmpeg

  I think I am misunderstanding what is meant by input framerate, and what is meant by output framerate. Could you help clarify ? I am using a Python script to call ffmpeg, as documented here : http://zulko.github.io/blog/2013/09/27/read-and-write-video-frames-in-python-using-ffmpeg/

  Here’s the output from the following manually executed command :

  ffmpeg -framerate 24/5 -i img%02d.png -c:v libx264 -r 30 -pix_fmt yuv420p test_output.mp4

  ffmpeg version N-75204-g314bc20 Copyright (c) 2000-2015 the FFmpeg developers
  
    built with gcc 4.9.3 (GCC)
  
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
  
  isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
  
  le-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --
  
  enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-l
  
  ibilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enab
  
  le-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --en
  
  able-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --ena
  
  ble-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc
  
   --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enabl
  
  e-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --ena
  
  ble-decklink --enable-opencl --enable-zlib
  
    libavutil      55.  2.100 / 55.  2.100
  
    libavcodec     57.  1.100 / 57.  1.100
  
    libavformat    57.  0.100 / 57.  0.100
  
    libavdevice    57.  0.100 / 57.  0.100
  
    libavfilter     6.  1.100 /  6.  1.100
  
    libswscale      4.  0.100 /  4.  0.100
  
    libswresample   2.  0.100 /  2.  0.100
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Input #0, image2, from 'img%02d.png':
  
    Duration: 00:00:00.42, start: 0.000000, bitrate: N/A
  
      Stream #0:0: Video: png, rgb24(pc), 800x400, 4.80 tbr, 4.80 tbn, 4.80 tbc
  
  File 'test_output.mp4' already exists. Overwrite ? [y/N] y
  
  [libx264 @ 0000000004f16ba0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
  
  AVX FMA3 AVX2 LZCNT BMI2
  
  [libx264 @ 0000000004f16ba0] profile High, level 3.0
  
  [libx264 @ 0000000004f16ba0] 264 - core 148 r2597 e86f3a1 - H.264/MPEG-4 AVC cod
  
  ec - Copyleft 2003-2015 - http://www.videolan.org/x264.html - options: cabac=1 r
  
  ef=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed
  
  _ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pski
  
  p=1 chroma_qp_offset=-2 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 dec
  
  imate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b
  
  _adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=
  
  25 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.
  
  60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to 'test_output.mp4':
  
    Metadata:
  
      encoder         : Lavf57.0.100
  
      Stream #0:0: Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 800x40
  
  0, q=-1--1, 30 fps, 15360 tbn, 30 tbc
  
      Metadata:
  
        encoder         : Lavc57.1.100 libx264
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (png (native) -> h264 (libx264))
  
  Press [q] to stop, [?] for help
  
  frame=   12 fps=0.0 q=-1.0 Lsize=       3kB time=00:00:00.33 bitrate=  62.2kbits
  
  /s dup=10 drop=0
  
  video:2kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing ove
  
  rhead: 60.557274%
  
  [libx264 @ 0000000004f16ba0] frame I:1     Avg QP:10.12  size:   566
  
  [libx264 @ 0000000004f16ba0] frame P:3     Avg QP:18.10  size:    62
  
  [libx264 @ 0000000004f16ba0] frame B:8     Avg QP:13.75  size:    22
  
  [libx264 @ 0000000004f16ba0] consecutive B-frames:  8.3%  0.0% 25.0% 66.7%
  
  [libx264 @ 0000000004f16ba0] mb I  I16..4: 99.4%  0.0%  0.6%
  
  [libx264 @ 0000000004f16ba0] mb P  I16..4:  0.0%  0.0%  0.0%  P16..4:  0.0%  0.0
  
  %  0.0%  0.0%  0.0%    skip:99.9%
  
  [libx264 @ 0000000004f16ba0] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8:  0.1%  0.0
  
  %  0.0%  direct: 0.0%  skip:99.9%  L0:37.5% L1:62.5% BI: 0.0%
  
  [libx264 @ 0000000004f16ba0] 8x8 transform intra:0.0% inter:0.0%
  
  [libx264 @ 0000000004f16ba0] coded y,uvDC,uvAC intra: 0.6% 0.0% 0.0% inter: 0.0%
  
   0.0% 0.0%
  
  [libx264 @ 0000000004f16ba0] i16 v,h,dc,p: 96%  0%  4%  0%
  
  [libx264 @ 0000000004f16ba0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 29% 18% 36%  2%  2%
  
   3%  3%  5%  1%
  
  [libx264 @ 0000000004f16ba0] i8c dc,h,v,p: 100%  0%  0%  0%
  
  [libx264 @ 0000000004f16ba0] Weighted P-Frames: Y:0.0% UV:0.0%
  
  [libx264 @ 0000000004f16ba0] ref P L0: 50.0% 50.0%
  
  [libx264 @ 0000000004f16ba0] kb/s:18.50