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• How can I learn the effective quality of the h264_nvenc encoder ?

  24 septembre 2020, par pfdint2

  I seek to ascertain the end-product quality of various cq ("constant quality") values for the h264_nvenc video encoder.

  


  To use the h264_nvenc encoder through ffmpeg and with a target quality, I follow the instructions in Nvidia's documentation, last paragraph of the linked anchor.

  


  I specify a Variable Bit Rate rate control mode (rc=vbr_hq) and a target quality (cq=). This should be enough to test various values of cq. The story should end there.

  


  HOWEVER, that only outputs the same perfect quality video of extremely large size for any cq value. (Using cq=1, cq=20, and cq=51 all output a file with the same hash.)

  


  Per documentation, I can also specify a maxBitRate (maxrate=). If I don't specify a maxrate, the documentation indicates :

  


  


  If maxBitRate is not specified, the encoder will use as many bits as needed to achieve the target quality.

  


  


  But that's not the behavior I'm observing. I'm seeing the encoder use as many bits as possible, not as many bits as needed. The resultant video has an overall bitrate of 100Mb/s. Double the source video.

  


  If I do set a maxrate, it is observed by the encoder. But if I have to set the bitrate correctly for every cq value, what is the point of the cq value ? I would just set cq=1 and test various bitrates, which would then only be applicable to a specific video.

  


  Is there some warning or output that notes that the bitrate was insufficient to reach the target quality that I'm not seeing ? That would at least allow me to brute force this.

  


  Or am I misunderstanding the relationship between these settings ?

  


• How can I learn the effective quality of the h264_nvenc encoder ?

  24 septembre 2020, par pfdint2

  I seek to ascertain the end-product quality of various cq ("constant quality") values for the h264_nvenc video encoder.

  


  To use the h264_nvenc encoder through ffmpeg and with a target quality, I follow the instructions in Nvidia's documentation, last paragraph of the linked anchor.

  


  I specify a Variable Bit Rate rate control mode (rc=vbr_hq) and a target quality (cq=). This should be enough to test various values of cq. The story should end there.

  


  HOWEVER, that only outputs the same perfect quality video of extremely large size for any cq value. (Using cq=1, cq=20, and cq=51 all output a file with the same hash.)

  


  Per documentation, I can also specify a maxBitRate (maxrate=). If I don't specify a maxrate, the documentation indicates :

  


  


  If maxBitRate is not specified, the encoder will use as many bits as needed to achieve the target quality.

  


  


  But that's not the behavior I'm observing. I'm seeing the encoder use as many bits as possible, not as many bits as needed. The resultant video has an overall bitrate of 100Mb/s. Double the source video.

  


  If I do set a maxrate, it is observed by the encoder. But if I have to set the bitrate correctly for every cq value, what is the point of the cq value ? I would just set cq=1 and test various bitrates, which would then only be applicable to a specific video.

  


  Is there some warning or output that notes that the bitrate was insufficient to reach the target quality that I'm not seeing ? That would at least allow me to brute force this.

  


  Or am I misunderstanding the relationship between these settings ?

  


• configure : Include the armcc build number in the compiler identification

  28 juillet 2014, par Martin Storsjö

  configure : Include the armcc build number in the compiler identification
  This tries to find the most expressive part of the output of
  
  armcc —vsn to include, giving a compiler identification of
  
  "ARM Compiler 5.04 update 2 (build 82)" instead of just
  
  "ARM Compiler 5.04" for armcc 5.0.
  4.x versions of armcc output the following, for "armcc —vsn" :
  
  ARM C/C++ Compiler, RVCT4.0 [Build 925]
  
  For evaluation purposes only
  
  Software supplied by : ARM Limited
  ARM C/C++ Compiler, 4.1 [Build 894]
  
  For evaluation purposes only
  
  Software supplied by : ARM Limited
  5.0 versions output this :
  
  Product : ARM Compiler 5.04
  
  Component : ARM Compiler 5.04 update 2 (build 82)
  
  Tool : armcc [5040081]
  
  For evaluation purposes only
  
  Software supplied by : ARM Limited
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DH] configure