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• FLV to MP4 conversion keeping PTS consistent

  16 janvier 2019, par M.Do

  The input file has the following video settings but playsback in media player at 29.97 FPS

  Video
  
  Format                      : AVC
  
  Format/Info                 : Advanced Video Codec
  
  Format profile              : Baseline@L2.1
  
  Format settings             : 2 Ref Frames
  
  Format settings, CABAC      : No
  
  Format settings, ReFrames   : 2 frames
  
  Codec ID                    : 7
  
  Duration                    : 1 min 30 s
  
  Width                       : 480 pixels
  
  Height                      : 360 pixels
  
  Display aspect ratio        : 4:3
  
  Frame rate mode             : Constant
  
  Frame rate                  : 14.985 (15000/1001) FPS
  
  Color space                 : YUV
  
  Chroma subsampling          : 4:2:0
  
  Bit depth                   : 8 bits
  
  Scan type                   : Progressive
  
  Color range                 : Limited
  
  Color primaries             : BT.601 NTSC
  
  Transfer characteristics    : BT.709
  
  Matrix coefficients         : BT.601

  However, another coded application will not accept the file as a valid file frame rates are only NTSC or PAL
  How can I force the frame rate to be presented as 29.97 without changing the duration of the clip ?

• Revision f7f0eaa581 : Add adaptation option for VBR. Allow min and maxQ to creep when the undershoot

  13 octobre 2014, par Paul Wilkins

  Changed Paths :
   Modify /vp9/encoder/vp9_firstpass.c

  
   Modify /vp9/encoder/vp9_firstpass.h

  
   Modify /vp9/encoder/vp9_ratectrl.c

  
   Modify /vp9/encoder/vp9_ratectrl.h

  
  
  Add adaptation option for VBR.

  Allow min and maxQ to creep when the undershoot
  or overshoot exceeds thresholds controlled by the
  command line under_shoot_pct and over_shoot_pct
  values.

  Default is 100%,100% which disables adaptation.

  Derf results for example undershoot% / overshoot% :-

  Head :- Mean abs (%rate error) = 14.4%

  This check in :-
  25%/25% - Mean abs (%rate error) = 6.7%
  PSNR hit -1% SSIM -0.1%

  5% / 5% - Mean abs (%rate error) = 2.2%
  PSNR hit -3.3% SSIM - 1.1%

  Most of the remaining error and most of the quality hit is
  at extreme data rates. The adaptation code still has an
  exception for material that is in effect static so that we
  don’t over adjust and over spend on YT slide show type
  content.

  (Rebase of If25a2449a415449c150acff23df713e9598d64c9
  to resolve a auto-merge error)

  Change-Id : Iec4e1613ef0d067454751d8220edb7058dfbd816

• FFMpeg unable to generate audio CBR

  20 décembre 2023, par Hitesh

  I am trying to transcode all videos with constant bit rate for both audio and video using ffmpeg. I am able to achieve this realistically for videos, however, audio is having multiple issues.

  


  Command being used :

  


  ffmpeg -benchmark -xerror -hide_banner -y -loglevel repeat+level+info 
-i 
-b:v 733k -minrate 733k -maxrate 733k -bufsize 733k -nal-hrd cbr 
-b:a 192k -threads 4 -vcodec libx264 -acodec aac -r 30.0 -af loudnorm=I=-23 output.mp4


  


  I tried checking output with mediainfo and tried plotting audio bit rates through plotbitrate library and can see variation in bit rate for certain videos.

  


  Here is one such sample :


  


  On other note, I am able to generate this through mediaconvert with consistent bit rate.

  


  Question is : Can we generate cbr audio through ffmpeg for videos where there are some silent zones and how ?