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• How to find the Quantified transformed coefficients in encoder x264 and in decoder libavcodec ?

  8 juillet 2019, par Quentin CHARRIER

  I’m a student in computer science and I am working on h264 encoder and decoder.

  I decided to use x264 and libavcodec and I downloaded code of these open libraries. Then, I searched for a month on how to do it. I think the quantified transformed coefficients are in h->dct.luma8x8 and h->dct.luma4x4 but they are no luma16x16 so I’m disappointed.

  Now, I suppose that Intra 16x16 macroblock have their coefficients in luma4x4 or luma8x8 but I’m not sure. Is there someone who knows about it and could give answers ?

  Furthermore, I have to find the same coefficients in decoder and I thought that they are in sl->mb but the coefficients in sl->mb are strange (there are a lot of 0s and values > 100 contrary to the encoder where values are close to 1-10..) I’m lost so I hope that someone have some advice to help me to continue my project.

  EDIT :

  I think the coefficients when the macroblock is encoded in 16x16IntraPrediction are in luma4x4. I always need help to understand how the decoder works.

  EDIT :

  I think the coefficients which are in sl->mb are always dequantized, maybe there is a variable who have the correct coefficient in decode_cabac_residual_internal but I didn’t find it..

• Error : "from : can't read /var/mail/moviepy.editor" How to resolve ?

  23 mai 2017, par batman_rising

  I have a script using which I am editing a video, (extracting 10 clips from a video and then simply concatenating them), I am using moviepy python module as well as ffmpeg

  The script works perfectly when I run it from terminal,

  Now I wanted to run the same script on startup, so I added a path in /etc/rc.local
sudo python /home/startlord/myProject/run.py but the code doesn’t work.

  also, I tried another approach,
  sudo nano /etc/init.d/testRun and created the script executable sudo chmod 755 /etc/init.d/testRun
  but when I wanted to start the execution sudo /etc/init.d/testRun start I was getting this error

  from : can’t read /var/mail/moviepy.editor

  what should I do now ! I am using UP-board, please help, I am not from computer science background.

• FFMPEG filter_complex wih speedup and subtitles and scaling

  11 décembre 2015, par Sambir

  Hi I am trying to convert a file to a specific framerate and remove any jittering, jumping of the screen. I also try to boost the volume and add a subtitle overlay. I get an error with the curent line than it is not allowed to use complex_filter in combination with vf and af. as an extra I also would like to add text in the left corner (this i did not try yet) and would want the screen to be sized to full hd (changed scale to 1920:1080 but no succes).

  ffmpeg -i movie.mp4 -r 25 -filter_complex "[0:v]setpts=0.959*PTS[v];[0:a]atempo=1.0427[a]" -map "[v]" -map "[a]" -vf subtitles=sub.srt,scale=1920:1080 -af volume=2 -strict -2 -preset veryfast movie_new.mp4

  Got it !

  New :

  ffmpeg -i inside.mp4 -r 25 -filter_complex "[0:v]setpts=0.959*PTS[i];[i]scale=1920:1080[j];[j]subtitles=inside.srt[k];[0:a]atempo=1.0427[p];[p]volume=2[q]" -map "[k]" -map "[q]" -strict -2 -preset veryfast inside_new.mp4

  But now there is a new issue. Subs out of sync :P is there a easy fix for this or do i first need to encode without subs then resync then encode with subs ?

  found this link by the way Subtitle Resync Tool

  moviespeed is changed by 0.959. is there a calculation i can do to adjust the subtitles by x miliseconds ?

  EDIT : Got the subtitles fixed with subtitle workshop. Was just a small setting to change which directly shifted all the text :)