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• ffmpeg - reading meta data value every 16ms to produce overlay

  18 avril 2022, par bcardarella

  I'd like to combine a few data sources for telemetry overlays over a video. The MP4s have some metadata embedded from my GoPro but I have a few other data sources I'd like to include. I already have a way to generate a PNG of the data visualizations. What I am wondering if is ffmpeg includes a way to, every 16ms to take the current video frame, get the corresponding metadata values for that frame embedded within the mp4, send them off to the image creator, take that output and overlay over the video frame.

  


  My assumption is that the mp4 metadata will correspond to the frame of the video. In that video frame's metadata the GPX values that I will need to generate the visualization.

  


• fluent-ffmpeg for getting codec data only

  15 février 2018, par agonza1

  I am using a fluent-ffmpeg node module for getting codec data from a file.
  It works if I give an output but I was wandering if there is any option to run fluent-ffmpeg without giving to it an output.
  This is what I am doing :

                  readStream.end(new Buffer(file.buffer));
  
                  var process = new ffmpeg(readStream);
  
  
  
                  process.on('start', function() {
  
                    console.log('Spawned ffmpeg');
  
                  }).on('codecData', function(data) {
  
                    //get recording duration
  
                    const duration = data.duration;
  
                    console.log(duration)
  
                  }).save('temp.flac');

  As you can see I am saving a the file to temp.flac so I can get the seconds duration of a file

• Encoding audio data using ffmpeg

  30 mai 2019, par Matin Kh

  I am receiving a byte array (int8_t*) and I would like to use FFMPEG to encode it into FLAC. All the examples I found are reading data from files, which is not the case for me. Following the original documents (see here), I came up with the following solution :

  #include "libavcodec/avcodec.h"
  
  
  
  // ...
  
  
  
  // params:
  
  //  audioData: original audio data
  
  //  len: length of the byte array (audio data)
  
  //  sampleRate: sample rate of the original audio data
  
  //  frameSize: frame size of the original data
  
  uint8_t* encodeToFlac(uint8_t* audioData, int len, int sampleRate, int frameSize) {
  
    uint8_t* convertedAudioData;
  
  
  
    // Context information
  
    AVCodecContext* context = avcodec_alloc_context();
  
    context->bit_rate = 64000;
  
    context->sample_rate = sampleRate;
  
    context->channels = 2;
  
    context->frame_size = frameSize;
  
  
  
    short* samples = malloc(frameSize * 2 * context->channels);
  
    int outAudioDataSize = len * 2;
  
    convertedAudioData = malloc(outAudioDataSize);
  
    int outSize = avcodec_encode_audio(c, convertedAudioData, outAudioDataSize, samples);
  
  
  
    return convertedAudioData;
  
  }

  I have two main issues with the above solution :

  1. I did not specify what the final encoding should be (for example, MP3, FLAC, etc), which makes me wonder if I’m using FFMPEG library correctly ?

  2. Do I have all the necessary information about the source - original audio data ? I am not certain if I have all the necessary information to perform the encoding.