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• FFMPEG - Struggling to find correct input audio codec parameters on macOS

  20 septembre 2024, par Xavi

  I am trying to read my external stereo microphone with ffmpeg within my Qt Windows+macOs application, but I am struggling to obtain consistent correct input codec parameters on macOs. My findings and suspicions so far :

  


  The code I'm using in macOs is the following, where everything returns a successful return code :

  


   avdevice_register_all();
 
 //macOs only, the same code in windows looks for "dshow" 
 const AVInputFormat *inputFormat = av_find_input_format("avfoundation");
 
 AVFormatContext* inputFormatContext;
 avformat_open_input(&inputFormatContext, inputDevice, inputFormat, NULL);

 avformat_find_stream_info(inputFormatContext, NULL);
 
 //... allocate the codec context for the single input stream and
 // copy the parameters from the stream to the context



  


  In my standalone minimal reproducer this always results on the codec ID of the single stream being AV_CODEC_ID_PCM_F32LE, in both macOS and Windows. When I integrate this code in my Qt application on Windows, I get the same result. However, on macOS, most of the times results in the codec id of the stream being AV_CODEC_ID_PCM_S16LE (via AV_CODEC_ID_FIRST_AUDIO) and sometimes AV_CODEC_ID_PCM_F32LE. Both sample formats are supported by my microphone.

  


  AV_CODEC_ID_PCM_F32LE always results in a correct output. AV_CODEC_ID_PCM_S16LE results on buzzy noisy audio slowed down to 0.5x, and If in this case I decode with AV_CODEC_ID_PCM_F32LE instead of copying the codec parameters from the stream, the output sounds correct again.

  


  I am trying to write generic code, so while enforcing the AV_CODEC_ID_PCM_F32LE codec works, I'd rather understand what is happening.

  


  What am I missing ? Is Qt interacting in some way that I can't think of ? I am compiling and linking my own ffmpeg libraries (6.1.1) and not using Qt's ones.

  


• avformat/format : silence -Wdiscarded-qualifiers

  19 septembre 2015, par Ganesh Ajjanagadde

  avformat/format : silence -Wdiscarded-qualifiers
  lpd.buf is non-const and discards the const qualifier of zerobuffer.
  
  This fixes -Wdiscarded-qualifiers observed with a variety of compilers, including GCC 5.2.
  
  Note that this does not change the type of zerobuffer, and merely makes the intent explicit.
  Signed-off-by : Ganesh Ajjanagadde <gajjanagadde@gmail.com>
  
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavformat/format.c

• colors messed up (distorted) when making a gif from png files using ffmpeg

  13 novembre 2019, par wxyz

  I have a sequence of png images : image_00.png, image_01.png, image_02.png, etc. I want to convert them to a gif, so I tried the command

  ffmpeg -i image_%02d.png video.gif

  Unfortunately, the resulting gif has distorted colors. More specifically, it added a weird sort of yellow haze around some objects in the video.

  I also tried using the command above with all possible pixel format options (which I determined using the command ffmpeg -h encoder=gif) : rgb8, bgr8, rgb4_byte, bgr4_byte, gray, pal8. For example ffmpeg -i image_%02d.png -pix_fmt rgb8 video.gif. Unfortunately, all of the resulting gifs had some sort of color distortion.

  I also observed that this distortion does not occur if I convert the images to mp4 instead of gif. However, if I try converting that mp4 to a gif, I end up with the distortion again.

  How can I produce this gif without color distortion ?