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• How to use ffmpeg / x264 2-Pass encoding for multiple bitrate output files

  2 décembre 2014, par Jonesy

  While performing a 2-Pass encode to multiple output files I was receiving the error

  ratecontrol_init: can't open stats file 1 ffmpeg2pass-2.log

  My setup is to do a single first pass and then multiple second pass encodes to output files with different target bitrates using the same first pass results.

  ffmpeg -y -i $INPUT_FILE -an -vcodec libx264 -pass 1 -b:v 700k -f rawvideo /dev/null
  
  
  
  ffmpeg -y -i $INPUT_FILE -i out-aud.mp4 \
  
  $AUDIO_OPTIONS_P2 -vcodec libx264 -pass 2 -b:v 250k -f mp4 out-250.mp4 \
  
  $AUDIO_OPTIONS_P2 -vcodec libx264 -pass 2 -b:v 500k -f mp4 out-500.mp4 \
  
  $AUDIO_OPTIONS_P2 -vcodec libx264 -pass 2 -b:v 700k -f mp4 out-700.mp4

  This sequence resulted in the error listed above. What I discovered thru code-inspection is that ffmpeg/x264 looks for a different set of first-pass files for each second-pass encoding path. The first encoding path uses the set of files originally created

  ffmpeg2pass-0.log
  
  ffmpeg2pass-0.log.mbtree

  The second encoding path requires first-pass files with the names

  ffmpeg2pass-2.log
  
  ffmpeg2pass-2.log.mbtree

  The third encoding path requires first-pass files with the names starting with ffmpeg2pass-4*, etc.

  My solution was to create soft-links to the originally created set of files with the new names that were required for each pass before running the second-pass command.

  ln -s ffmpeg2pass-0.log ffmpeg2pass-2.log
  
  ln -s ffmpeg2pass-0.log.mbtree ffmpeg2pass-2.log.mbtree
  
  ln -s ffmpeg2pass-0.log ffmpeg2pass-4.log
  
  ln -s ffmpeg2pass-0.log.mbtree ffmpeg2pass-4.log.mbtree

  This seems to work as it results in the output encodes that I needed. However, I don’t know if this method is legitimate. Am I getting sub-optimal encoding results by using a first-pass output for one bitrate (700k) as the input to second-pass encodings for other bitrates ?

• Image scaling boundaries in FFMEG

  6 mars 2018, par Pedro Pereira

  I am implementing my own version of the bilinear and bicubic scaling algorithms to understand how ffmpeg does the scaling. So, I compare the results I get with the results of the ffmpeg. A couple days agora I had trouble implementing the bilinear version because my bilinear scaled images were different from the ffmpeg ones. With the help of people in the IRC chat I understood that the ffmpeg duplicates the nearest original pixel when the index of the neighboring pixels to interpolate is out of the original image bounds.

  In the same perspective, what does the bicubic version in ffmpeg does to out of the original bounds pixels ? I tried duplicating the nearest original pixel (like in bilinear) and my scaled image is not the same as the ffmpeg one.

  Do I have to something like this ? Fill the boundaries of a matrix using Bicubic interpolation

• Ordering FFMPEG Elements

  14 avril 2020, par deeeepnet

  I'm working on FFMPEG with Jetson nano and PC.
I want to know the ordering element of FFMPEG can be effect in the result ? Is it necessory to observe the ordering of elements ?

  



  In the concept of decoding and encoding streams :

  



  


  ffmpeg -hwaccel cuvid -c:v h264_nvdec -c:v h264_cuvid -i input -c:v
 h264_nvenc output

  


  



  If I replace the -hwaccel cuvid with -c:v h264_nvdec, such as :

  



  


  ffmpeg -c:v h264_nvdec -c:v h264_cuvid -hwaccel cuvid -i input -c:v
 h264_nvenc output

  


  



  Q1- May be these two above commands corecttly run, but in the backgrand these two commands have same operations and results ?

  



  Q2 -Or if I want to put -hwaccel cuvid after -i input, are these two commands have same operations and results ?