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• Configure AVCodecContext structure to encode from raw PCM to u-law

  15 mai 2017, par N0un

  I’m trying to encode raw PCM audio data to u-law and it’s sound very weird (when it sounds...). I don’t understand pretty much how to initialize my AVCodecContext structure (and my input AVFrame).

  Here are my parameters :

  • Input : PCM (16bits signed), MONO, 44,1kHz (sample rate) (from my Android device MIC)

  • Required output : G.711 u-law, MONO, 8kHz (sample rate), 64 kbits/s (bitrate) (from my output target device’s documentation)

  I also know my input nb samples and this is all informations I have.

  So I initialize my AVCodecContext like that :

  AVCodec* pCodec = avcodec_find_encoder(AV_CODEC_ID_PCM_MULAW);
  
  // ...
  
  AVCodecContext* pCodecContext = avcodec_alloc_context3(pCodec);
  
  // ...
  
  // Do I need input or output params in following lines?
  
  pCodecContext->channels = 1:
  
  pCodecContext->channel_layout = AV_CH_LAYOUT_MONO;
  
  pCodecContext->sample_rate = 8000;
  
  pCodecContext->bit_rate = 64000
  
  pCodecContext->sample_fmt = AV_SAMPLE_FMT_S16;

  And my AVFrames like :

  AVFrame* pFrame = av_frame_alloc();
  
  pFrame->channels = 1;
  
  pFrame->channel_layout = AV_CH_LAYOUT_MONO;
  
  pFrame->sample_rate = 44100;
  
  pFrame->format = AV_SAMPLE_FMT_S16;
  
  pFrame->nb_samples = /*my audio data samples count*/;
  
  avcodec_fill_audio_frame(pFrame, 1, AV_SAMPLE_FMT_S16, /*my audio data*/, /*my audio data size*/, 0);

  Then, I encode with avcodec_send_frame() and avcodec_receive_packet().

  So my problem is that I’m not sure if I have to put input or output desired values in different parameters. Probably I have to encode on a way then "resample" using swresample lib. But for now, I’m pretty sure that I don’t encode properly. Any advise please ? Thanks !

• ffmpeg reencoding 1080p to 720p with subtitles

  9 juin 2019, par Jon Glazer

  I am just trying to re-encode 1080p MKV files down to 720p. The command line I have (below) works pretty well but I just realized it is not encoding the embedded subtitle stream to the 720p output. How can I do this ?

  ffmpeg -i "video1.mkv" -c:v libx264 -crf 23 -preset medium -c:a aac -b:a 128k -movflags +faststart -vf scale=-2:720,format=yuv420p ".mkv"

• How to overlay frames before making a gif FFMPEG WEBM TO GIF

  10 février 2021, par AVID_FFMPEG

  I'm using windows batch to do some ffmpeg work

  


  Basically what I need to do is this

  


  Add an overlay every X frames (10 in this example, 1, 11 , 21 and so on) to a webm source to a gif.

  


  The how doesn't really matter as long as I keep the quality of my current palette/filter/dither usage

  


  Solution I found : I made a Video to png, overlay the png with batch for loop and make a gif

  


  Problem I encountered : Gif doesn't work with the overlayed pngs

  


  rem EXTRACTING
ffmpeg !time_range! -i "input.webm" -vsync 0 -vf "fps=20,scale=!size!" "output_%%03d.png" 


  


  the two %% is because you need to escape it in batch so ffmpeg sees "%03d"

  


  REM OVERLAYING
for %%i in (_*1.png) do (
ffmpeg -y -v error -i %%i -i %tmp_blank_frame% -filter_complex "overlay"  overlayed_%%~nxi
del %%i
)
REM REPLACING
rename "overlayed_*" "//////////*"


  


  It is not pretty by any means, but it works... somewhat.

  


  It does it's job of overlaying and renaming proprely, but when I recompile the frames into a gif with

  


  ffmpeg -y -framerate 20 -i "output_%%03d.png" -i "!palette!" -filter_complex "!filters! [v]; [v][1:v] paletteuse=dither=!dither!" "overlayedgif.gif"


  


  it just gives me an error "Error marking filters as finished" and does nothing.

  


  ffmpeg -y -framerate 20 -i "output_%%03d.png" -i "!palette!" "overlayedgif.gif"


  


  It makes the gif without the black frames (skips them) also terrible quality

  


  I am open to any suggestion. Pretty new to this whole ffmpeg and this is starting to be very complicated for me so there might be some code that I overlook or don't fully understand

  


  Important note IF I REMOVE THE OVERLAY/RENAME BLOCK MY SCRIPT WORKS WONDERS !!!

  


  EDIT : edited confusing variables im using in my script