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• 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.

• How to Identify the Version of ffmpeg.dll in WebView2 Runtime Fixed Version

  19 février, par Po-Sen

  I am currently using the WebView2 runtime fixed version. After expanding the package, I found multiple DLL files, including ffmpeg.dll.

  


  In the file properties, the file version is displayed as 0.0.0.0, and the only version-related information I can see is the product version : git-2024-04-25-e3581fa2dd.

  


  

  


  This format is different from the numeric versioning scheme I see on the official FFmpeg website : https://ffmpeg.org/download.html#releases.

  


  

  


  I want to trace the exact FFmpeg version used in this WebView2 distribution.
Initially, I assumed e3581fa2dd was a Git commit SHA. However, after cloning the FFmpeg repository from https://git.ffmpeg.org/ffmpeg.git, I could not find this commit.

  


  Our product was recently scanned and found to contain FFmpeg version 3.4.2, which has known CVE security vulnerabilities. Therefore, we want to clarify the actual version of FFmpeg included in the WebView2 runtime.

  


  How can I determine the version of ffmpeg.dll included in WebView2 runtime fixed version ?

  


• 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.