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• poor resolution in video out put from ffmpeg

  27 janvier 2019, par Clinton Winant

  I make animation of png or jpg frames output from a fluid flow simulation code. An example image looks like :
  

  The ffmpeg command I use is

  ffmpeg  -f image2 -r 20 -i img%04d.png -vcodec mpeg4 animate.avi

  The resulting video is very poor as can be seen in the screen capture of a single frame of the output file animate.avi :

  

  There are elongated shaded areas on either side of the yellow streaks, and the ffmpeg produced frame is much grainier than the original .png.

  I understand that there has to be massive compression in the production of the video, and I assume the problem lies there, where the compression id poor for the kind of images I am trying to animate. How could I use ffmpeg to produce a video with quality comparable to the original images I have ?

  PS I am using Debian Buster, the png images have a resolution of 100 dpi.

• Adjusting watermark according to video resolution using ffmpeg [duplicate]

  1er février 2019, par Awais fiaz

  This question already has an answer here :

  • How to scale and add correct a logo in ffmpeg command ?
    
    1 answer
    

  I have a question related to video conversion I am trying to add watermark to different high resolution videos using ffmpeg and its getting added pretty fine but the issue is same watermark gets bigger on low resolution videos which was looking fine with high resolution video.Is there any possible way i can scale watermark according to video resolution ?.I am sure there is but I seem to be pretty blank in this area any help regarding this issue would be really appreciated.

  This is the command that i am using to add watermark in my php script

  /usr/bin/ffmpeg -i /var/www/html/demo/files/conversion_queue/15490094394e7a7.mp4 -i /var/www/html/demo/upload/images/watermark.png -filter_complex 'overlay=10:10' -y /var/www/html/cb_corp_git/upload/files/conversion_queue/15490094394e7a7-wm.mp4 

• Can't fix timestamp of WebM video with dynamic resolution using FFmpeg

  11 février 2019, par Yurii Kit

  I’m developing the platform for 1-1 video calls with recording. For my purposes, I work with the following stack : WebRTC, Kurento Media Server, FFmpeg.

  1. It works perfectly in an ideal environment, but if my users have a poor connection, after the recording I see a lot of problems with the out of sync audio and video tracks.

     As I understand, the problem appears due to the incorrect timestamp, so I’m doing a bit post-processing where I generate a new timestamp and it helps !

     Here is the command example :

     ffmpeg -fflags +genpts -acodec libopus -vcodec libvpx \
     
         -i in.webm \
     
         -filter_complex "fps=30, setpts=PTS-STARTPTS" \
     
         -acodec libvorbis -vcodec libvpx \
     
         -vsync 1 -async 1 -r 30 -threads 4 out.webm

  2. After that, I’ve faced one more problem. If the user has a poor connection, WebRTC can dynamically change the video resolution. After the post-processing for such type of videos (with the different resolutions during the video) I see the frozen image until the end of the video and it started from the moment, where the resolution was dynamically changed. There are no error in the FFmpeg logs, just information about changing the resolution :

     [libvpx @ 0x559335713440] dimension change! 480x270 -> 320x180
     
     -async is forwarded to lavfi similarly to -af aresample=async=1:min_hard_comp=0.100000.

     After analyzing the logs, I realized that the problem was due to the STARTPTS parameter, which, after automatically changing the extension, became very large (equal to the number of frames that were before it). I tried to remove STARTPTS and leave only PTS.

     After that, the video started to work well, but only until the video resolution are dynamically changed, then again the audio and video tracks are out of sync.

     I’ve tried to scale videos to a static resolution before fixing timestamp and it helps. But it’s a little bit extra work. Command example :

     ffmpeg -acodec libopus -vcodec libvpx \
     
         -i in.webm \
     
         -vf scale=640:480 \
     
         -acodec libvorbis -vcodec libvpx \
     
         -threads 4 out.webm

     Also I’ve tried to combine both commands using filter_complex, but it didn’t work.

     I’ve worked with FFmpeg not so many time so far, so, maybe I’m doing something wrong ? Maybe there are some easier ways to do that ?

     Since Kurento uses GStreamer for the video recording, so maybe it would be a better option to reconfigure Kurento to fix timestamp during the video recording ?

  I can provide any videos and commands which I use.

  I’m using :
  Kurento Media Server 6.9.0,
  FFmpeg 4.1