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• ffmpeg quality conversion options (video compression)

  25 septembre 2020, par Jason Hunter

  Can you provide a link, or an explanation, to the -q:v 1 argument that deals with video/image quality, and compression, in ffmpeg.

  


  Let me explain...

  


  for f in *
   do 
     extension="${f##*.}"
     filename="${f%.*}"
     ffmpeg -i "$f" -q:v 1 "$filename"_lq."$extension"
     rm -f "$f"
   done


  


  The ffmpeg for loop above compresses all images and videos in your working directory, it basically lowers the quality which results in smaller file sizes (the desired outcome).

  


  I'm most interested in the -q:v 1 argument of this for loop. The 1 in the -q:v 1 argument is what controls the amount of compression. But I can't find any documentation describing how to change this value of 1, and describing what it does. Is it a percentage ? Multiplier ? How do I adjust this knob ? Can/should I use negative values ? Integers only ? Min/max values ? etc.

  


  I started with the official documentation but the best I could find was a section on video quality, and the -q flag description is sparse.

  


  


  -frames[:stream_specifier] framecount (output,per-stream)
  
Stop writing to the stream after framecount frames.
  
.
  
-q[:stream_specifier] q (output,per-stream)
  

  
-qscale[:stream_specifier] q (output,per-stream)
  
Use fixed quality scale (VBR). The meaning of q/qscale is codec-dependent. If qscale is used without a stream_specifier then it applies only to the video stream, this is to maintain compatibility with previous behavior and as specifying the same codec specific value to 2 different codecs that is audio and video generally is not what is intended when no stream_specifier is used.

  


  


• Piwik 2 reaches end of life soon (December 2017), update now !

  7 décembre 2017, par Piwik Core Team — Community

  In less than three weeks, Piwik 2 will be no longer supported. This means that no further (security) updates will be released for this version. As per our Long Term Support announcement, Piwik 2.X is supported for 12 months after the initial release of Piwik 3.0.0 which was on December 18th 2016. Therefore, Piwik 2 will no longer receive any updates after December 18th 2017.

  It has been almost a year since we released Piwik 3 and we highly recommend updating to Piwik 3 ASAP. The major new release came with a new UI, performance and security improvements. If you are still on Piwik 2, the security improvements alone should be worth updating your Piwik to Piwik 3 now. We cannot recommend this enough.

  The update to Piwik 3 should be smooth, but may take a while depending on the amount of data you have.

  • If you have any problem with the update, feel free to get in touch with us, or ask in the forums.
  • If you are currently using Piwik self-hosted and would like to be upgraded, plus your Piwik managed in the official Cloud-hosted service, contact InnoCraft Cloud and they will migrate your database.

  At Piwik and InnoCraft, the company of the makers of Piwik, we have seen many thousands of Piwik installations upgraded over the past year and look forward to an exciting future for Piwik 3 and beyond !

• sws_scale screws up last pixel row in smaller x264 mp4 encoding

  23 juillet 2012, par TheSHEEEP

  I am muxing pictures in the PIX_FMT_ARGB format into an mp4 video.

  All of it works well, except that the last pixel row of the outgoing image is screwed up, in most cases the last row is completely black, sometimes there are other colors, it seems somehow dependant on the machine it runs on.

  I am absolutely sure that the error must be in sws_scale, as I am saving the images before and after the scaling. The input images do not have the error, but after the sws_scale() I save the yuv image and the error is apparent.

  Here is an example :

  Original

  

  Yuvfile (after sws_scale)

  

  At the bottom of the Yuvfile, you will see the black row.

  This is how I do the scaling (it is after the official ffmpeg examples, more or less) :

  static int sws_flags = SWS_FAST_BILINEAR | SWS_ACCURATE_RND;
  
  
  
  if (img_convert_ctx == NULL)
  
  {
  
     img_convert_ctx = sws_getContext( srcWidth, srcHeight,
  
             PIX_FMT_ARGB,
  
             codecContext->width, codecContext->height,
  
             codecContext->pix_fmt,
  
             sws_flags, NULL, NULL, NULL );
  
     if (img_convert_ctx == NULL)
  
     {
  
        av_log(c, AV_LOG_ERROR, "%s","Cannot initialize the conversion context\n");
  
        exit(1);
  
     }
  
  }
  
  fill_image(tmp_picture, pic, pic_size, frame_count, ptr->srcWidth, ptr->srcHeight );
  
  
  
  sws_scale(img_convert_ctx, tmp_picture->data, tmp_picture->linesize,
  
          0, srcHeight, picture->data, picture->linesize);

  I also tried a number of different SWS_ flags, but all yield the same result.

  Could this be a bug in sws_scale or am I doing something wrong ? I am using the latest version of the ffmpeg libraries.