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• ffmpeg - how can I get a specific channel using channel masks (e.g. : get only surround left channel)

  26 novembre 2013, par awfulcode

  I'm trying to build a mixer that allows users to toggle specific channels on and off. I know that different codecs encode those channels in different orders (it's not as simple as getting channel #3 as the center channel every time), so the challenge is to properly identify the channel position in surround audio tracks.

  ffmpeg does list the in the beginning of libavutil/channel_layout.h :

  #define AV_CH_FRONT_LEFT             0x00000001
  
  #define AV_CH_FRONT_RIGHT            0x00000002
  
  #define AV_CH_FRONT_CENTER           0x00000004
  
  #define AV_CH_LOW_FREQUENCY          0x00000008
  
  #define AV_CH_BACK_LEFT              0x00000010
  
  #define AV_CH_BACK_RIGHT             0x00000020
  
  #define AV_CH_FRONT_LEFT_OF_CENTER   0x00000040
  
  #define AV_CH_FRONT_RIGHT_OF_CENTER  0x00000080
  
  #define AV_CH_BACK_CENTER            0x00000100
  
  #define AV_CH_SIDE_LEFT              0x00000200
  
  #define AV_CH_SIDE_RIGHT             0x00000400
  
  #define AV_CH_TOP_CENTER             0x00000800
  
  #define AV_CH_TOP_FRONT_LEFT         0x00001000
  
  #define AV_CH_TOP_FRONT_CENTER       0x00002000
  
  #define AV_CH_TOP_FRONT_RIGHT        0x00004000
  
  #define AV_CH_TOP_BACK_LEFT          0x00008000
  
  #define AV_CH_TOP_BACK_CENTER        0x00010000
  
  #define AV_CH_TOP_BACK_RIGHT         0x00020000
  
  #define AV_CH_STEREO_LEFT            0x20000000  ///< Stereo downmix.
  
  #define AV_CH_STEREO_RIGHT           0x40000000  ///< See AV_CH_STEREO_LEFT.
  
  #define AV_CH_WIDE_LEFT              0x0000000080000000ULL
  
  #define AV_CH_WIDE_RIGHT             0x0000000100000000ULL
  
  #define AV_CH_SURROUND_DIRECT_LEFT   0x0000000200000000ULL
  
  #define AV_CH_SURROUND_DIRECT_RIGHT  0x0000000400000000ULL
  
  #define AV_CH_LOW_FREQUENCY_2        0x0000000800000000ULL

  But looking over the header files and whatever little documentation about ffmpeg I couldn't find anything that tells me how to assign a specific channel position (or mask, as it's described in the header file) to a specific bus in a mixer audio unit.

  Do you know how to do that ? Please let me know if you want to look at the code I'm using right now.

  And as always, thank you so much.

• Writing linear float range to openEXR turns out non linear

  3 avril 2022, par Chryfi

  I am writing the linearized depth buffer of a game to openEXR using FFmpeg. Unfortunately, FFmpeg does not adhere to the openEXR file specification fully (like allowing unsigned integer for one channel) so I am writing one float channel to openEXR, which is put into the green channel with this command -f rawvideo -pix_fmt grayf32be -s %WIDTH%x%HEIGHT% -r %FPS% -i - -vf %DEFVF% -preset ultrafast -tune zerolatency -qp 6 -compression zip1 -pix_fmt gbrpf32le %NAME%_depth_%d.exr.

  


  The float range is from 0F to 1F and it is linear. I can confirm that the calculation and linearization is correct by testing 16 bit integer (per pixel component) PNG in Blender compositor. The 16 bit integer data is written like this short s = (short) (linearzieDepth(depth) * (Math.pow(2,16) - 1)) whereas for float the linearized value is directly written to OpenEXR without multiplying with a value.

  


  However, when viewing the openEXR file it doesn't have the same "gradient" as the 16 bit png... when viewing them side by side, it appears as if the values near 0 are not linear, and they are not as dark as they should be like in the 16 bit png.
(And yes, I set the image node to linear), and comparing it with 3d tracking data from the game I cant reproduce the depth and cant mask things using the depth buffer where as with the png I can.

  


  How is it possible for a linear float range to turn out so different to a linear integer range in an image ?

  


• ffmpeg - DF vs NDF (Drop Frames) vs (Non Drop Frames), how to simply pass input timecode to output

  24 septembre 2020, par Selene

  Please help with this issue. The broadcaster just rejected my submitted video because their validation tool threw this kind of error :

  


  


  was configured as "Non drop Frame". "Drop Frame" expected.

  


  


  I'm only processing video, and I expect the audio to just be copied from input to output.
Running and comparing input with output using ffprobe shows difference in timecode :

  


    Metadata:
    major_brand     : qt  
    minor_version   : 537199360
    compatible_brands: qt  
    creation_time   : 2020-02-29T22:07:42.000000Z
  Duration: 00:00:20.05, start: 0.000000, bitrate: 133935 kb/s
    Stream #0:0(eng): Video: dvvideo (dvh6 / 0x36687664), yuv422p(bt709, top coded first (swapped)), 1280x1080 [SAR 3:2 DAR 16:9], 115084 kb/s, 29.97 fps, 29.97 tbr, 30k tbn, 29.97 tbc (default)
    Metadata:
      creation_time   : 2020-02-29T22:07:42.000000Z
      handler_name    : Apple Video Media Handler
      encoder         : DVCPRO HD 1080i60
      timecode        : 00:00:00;00
    Stream #0:1(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, mono, s32 (24 bit), 1152 kb/s (default)
    Metadata:
      creation_time   : 2020-02-29T22:07:42.000000Z
      handler_name    : Apple Sound Media Handler
      timecode        : 00:00:00;00
    Stream #0:2(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, mono, s32 (24 bit), 1152 kb/s (default)
    Metadata:
      creation_time   : 2020-02-29T22:07:42.000000Z
      handler_name    : Apple Sound Media Handler
      timecode        : 00:00:00;00
    Stream #0:3(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, mono, s32 (24 bit), 1152 kb/s (default)
    Metadata:
      creation_time   : 2020-02-29T22:07:42.000000Z
      handler_name    : Apple Sound Media Handler
      timecode        : 00:00:00;00


  


  After video conversion, the output of ffprobe :

  


    Metadata:
    major_brand     : qt  
    minor_version   : 512
    compatible_brands: qt  
    encoder         : Lavf58.58.100
  Duration: 00:00:20.05, start: 0.000000, bitrate: 167037 kb/s
    Stream #0:0(eng): Video: prores (XQ) (ap4x / 0x78347061), yuv422p12le(tv, bt709, top coded first (swapped)), 1920x1080, 148578 kb/s, SAR 1:1 DAR 16:9, 29.97 fps, 29.97 tbr, 30k tbn, 30k tbc (default)
    Metadata:
      handler_name    : Apple Video Media Handler
      encoder         : Lavc58.106.100 prores_ks
      timecode        : 00:00:00:00
    Stream #0:1(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, 1 channels, s32 (24 bit), 1152 kb/s (default)
    Metadata:
      handler_name    : Apple Sound Media Handler
    Stream #0:2(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, 1 channels, s32 (24 bit), 1152 kb/s (default)
    Metadata:
      handler_name    : Apple Sound Media Handler
    Stream #0:3(eng): Audio: pcm_s24le (in24 / 0x34326E69), 48000 Hz, 1 channels, s32 (24 bit), 1152 kb/s (default)
    Metadata:
      handler_name    : Apple Sound Media Handler


  


  My encoding string looks like this :

  


  ffmpeg -i input.mov -vf scale=1920x1080 -map 0:v? -map 0:a? -map 0:s? -map 0:d? -b:v 115084915 -maxrate 115084915 -minrate 115084915 -c:v prores_ks -profile:v 5 -preset ultrafast -crf 0 -c:a copy -c:s copy -y output.mov


  


  Please help !