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• ffmpeg transcoding : Metallic distorsion on macOS

  10 septembre 2024, par Xavi

  I am following ffmpeg's transcoding.c example to record audio and video from my input devices into an mp4 output file with H264 and AAC as codecs. I have no issues with the video and the audio transcoding works correctly on Windows.

  


  However, on macOS I have an issue with any input device other than the internal microphone of my laptop : the audio comes out distorted and sounding noisy and metallic (sample recording claps : https://file.io/nEn8MXHUAUQ2). I went through the input and output parameters for the filter several times, checked the values, but there must be something I'm missing. And I can't explain why it works on Windows with the same devices.

  


  Has anyone run into a similar problem before ? Any idea where I should start looking at ?

  


  Additional comments :

  


  

  1. While the Macbook's internal microphone (the only one that works) has only one channel, the other microphones I have available are stereo, so I can't say for sure that that's where the problem is.

  


  2. I also tested it on a macbook mini, with the same results.

  


  3. ffmpeg 6.1.1, MacOs 14.5

  


  4. Input filter arguments : time_base=1/1000000:sample_rate=48000:sample_fmt=1:channel_layout=stereo

  


  5. Output filter arguments : setpts=PTS-STARTPTS,aresample=48000:async=1:out_sample_fmt=8:out_chlayout=stereo,asetnsamples=n=1024

  


  


• avdevice/decklink : 10 Bit support for Decklink input device

  18 janvier 2015, par Georg Lippitsch

  avdevice/decklink : 10 Bit support for Decklink input device
  Example to capture video clip at 1080i50 10 bit :
  
  ffmpeg -bm_v210 1 -f decklink -i ’UltraStudio Mini Recorder@11’ -acodec copy -vcodec copy output.avi
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavdevice/decklink_common_c.h
  • [DH] libavdevice/decklink_dec.cpp
  • [DH] libavdevice/decklink_dec_c.c

• FFmpeg, how to skip late input ?

  14 novembre 2017, par user3343357

  I’m running ffmpeg to display incoming stream on a Decklink BlackMagic card with the following command line :

  ffmpeg -y -f ourFmt -probesize 32 -i - -f decklink -preset ultrafast 
  
     -pix_fmt uyvy422 -s 1920x1080 -r 30 -af volume=0.1 -max_delay 10000 
  
       DeckLink Mini Monitor

  Basically I get the video over the internet by UDP and stream it to ffmpeg stdin. Both audio and video streams have pts and dts and are fully in sync, if the connection is good there is no problems.

  However if there are issues with the connection i start getting errors, sometimes the video delay grows significantly, and audio stops working.
  The errors i get are :

  ffmpeg : [decklink @ 0x26cc600] There are not enough buffered video
  frames. Video may misbehave ! ffmpeg : [decklink @ 0x26cc600] There’s no
  buffered audio. Audio will misbehave ! ffmpeg : Last message
  repeated 4 times ffmpeg : [decklink @ 0x26cc600] There are not enough
  buffered video frames. Video may misbehave ! ffmpeg : [decklink @
  0x26cc600] There’s no buffered audio. Audio will misbehave ! ffmpeg :
  Last message repeated 3 times ffmpeg : frame= 5204 fps= 30 q=-0.0
  size=N/A time=00:02:53.76 bitrate=N/A dup=385 drop=5 speed=0.993x
  ffmpeg : [decklink @ 0x26cc600] There’s no buffered audio. Audio will
  misbehave ! ffmpeg : Last message repeated 18 times ffmpeg :
  [decklink @ 0x26cc600] There are not enough buffered video frames.
  Video may misbehave ! ffmpeg : [decklink @ 0x26cc600] There’s no
  buffered audio. Audio will misbehave !

  The problem is when the connection is back to normal, the video keeps misbehaving until I restart the stream. What I want to do is for FFmpeg to skip to the content of the last second and play synchronized video from there, drop all the late data in between, is it possible ?