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• Thread Safety of LibAv/FFMpeg ?

  14 septembre 2022, par user71512

  Is LibAV/FFMpeg thread safe ? For example. Could I read from a file using AVFormatContext* in one thread and decode the read packet it in another with simple additions of mutexes or is the thread safetyness of the library a "don't know don't care" type deal ? I know that libav has basic support for encoder threads but I'm trying more of a blackbox type approach where I break it up into multiple threads (Source -> Decoder -> Filter -> Encoder -> Sink) and trying to understand the complications of such.

  


  Anyone with any experience with ffmpeg and threads and would like to chime in with any other info pertinent to this would also be greatly appreciated.

  


• ffmpeg watermark without background [closed]

  22 décembre 2022, par Edwin Pitters

  I have a problem, I am trying to add a watermark to my videos with ffmpeg using a gtx 1060 graphics card, the process works well and very fast, the problem is that the watermark appears with a black background , the image has no background, it is transparent, the problem happens only when I use the nvidia graphics card, because if I do the process with my processor the watermark is placed correctly as expected, so I am sure it is a problem in my configuration when running ffmpeg

  


  Here I leave the command that I am using :

  


  .\ffmpeg.exe -y -hide_banner -init_hw_device cuda=cuda -filter_hw_device cuda -hwaccel cuda -hwaccel_output_format cuda -i test.mp4 -i watermark.png -filter_complex "[1:v]colorchannelmixer=aa=0.3,scale=iw*0.6:-1,format=nv12,hwupload[img];[0:v][img]overlay_cuda=x='if(lt(mod(t\,16)\,8)\,W-w-W*10/100\,W*10/100)':y='if(lt(mod(t+4\,16)\,8)\,H-h-H*5/100\,H*5/100)'[out]" -map [out] -c:v h264_nvenc -b:v 6M -an -preset fast out_overlay.mp4


  


  If I use my processor with the following command, the guide mark without background is added, that is, as expected

  


  for %%a in ("*.m*") do ffmpeg -y -hide_banner -threads 4 -i "%%a" -preset ultrafast -vcodec libx264 -b:v 4000k -minrate 4000k -maxrate 4000k -bufsize 4000k -c:a aac -b:a 64k -pass 1 -f mp4 NUL && ffmpeg -y -hide_banner -threads 8 -i "%%a" -i watermark.png -preset ultrafast -vcodec libx264 -b:v 4000k -minrate 4000k -maxrate 4000k -bufsize 4000k -filter_complex "[1]colorchannelmixer=aa=0.3,scale=iw*0.8:-1[a];[0][a]overlay=x='if(lt(mod(t\,8)\,4)\,W-w-W*10/100\,W*10/100)':y='if(lt(mod(t+2\,8)\,4)\,H-h-H*10/100\,H*10/100)'" -c:a copy -tune film -movflags +faststart -pass 2 "watermark/%%a"
pause


  


  I also tried changing colorchannelmixer=aa=0.3 for lut=a=val*0.3 but it seems that this command is not having any effect

  


  I find that the image is well reviewed to discard, in fact I tried with other images also with a transparent background and I have the same result, a watermark but with a black background

  


• Scripting FFmpeg to move text in y co-ordinate by some delta at specific time-codes

  27 février 2019, par distro.obs

  I’m using the basic drawtext command like this

  ffmpeg -i output.mp4 -vf \
  
  'drawtext=textfile='textfile.txt':x=0:y=0 \
  
  :fontsize=30:fontcolor=white:borderw=3 \
  
  :bordercolor=black:box=0' output.mp4"

  which puts stationary text at location (x, y) = (0,0)

  What I want to do is move this text by 10 points in y plane at certain time codes.

  at 00:00:10, y would be 0
  
  at 00:00:11, y would be 10
  
  at 00:00:43, y would be 20
  
  ...
  
  ...
  
  at 00:10:44, y would be 30

  so the ’y’ co-ordinate has a fix increment of 10 at ’keytimes’

  Is there a way to do that ?