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• FFMpegCore .Net cuts off the fist few ( 1.5) seconds of audio

  28 mai 2024, par Tim

  I want to use FFMpegCore to convert some audio files to raw pcm. I noticed that this always cuts off 1.5 seconds of my audio from the start. I check my input stream, saved it to HD all good. If use it from cli with the same arguments everything seem fine. I tried -ss 0, no luck. This behavior is observed with .wav (RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 44100 Hz), same issue with different sample rate. I tested mp3 works fine.

  


  public async Task<memorystream> ConvertToPcmStreamAsync(Stream inputStream)&#xA;{&#xA;    var outputStream = new MemoryStream();&#xA;    &#xA;    var audioInput = new StreamPipeSource(inputStream);&#xA;    var audioOutput = new StreamPipeSink(outputStream);&#xA;&#xA;    await FFMpegArguments&#xA;        .FromPipeInput(audioInput)&#xA;        .OutputToPipe(audioOutput, options => options&#xA;            .WithCustomArgument("-ss 0 -f s16le -acodec pcm_s16le -ac 1"))&#xA;        .ProcessAsynchronously();&#xA;&#xA;    // Reset the position of the memory stream to the beginning&#xA;    outputStream.Position = 0;&#xA;&#xA;    return outputStream;&#xA;}&#xA;</memorystream>

  


• avformat/aacdec : enable probesize-sized resyncs mid-stream

  27 septembre 2021, par Jan Ekström

  avformat/aacdec : enable probesize-sized resyncs mid-stream
  Before adts_aac_resync would always bail out after probesize amount
  
  of bytes had been progressed from the start of the input.
  Now just query the current position when entering resync, and at most
  
  advance probesize amount of data from that start position.
  Fixes #9433
  

  • [DH] libavformat/aacdec.c

• ffprobe (ffmpeg) seek in audio wave file

  26 avril 2019, par loretoparisi

  I’m using ffprobe to seek to position on mp3 files, and it works ok. This is how I do in my ffprobe node.js wrapper :

  seek = function (fpath, seconds) {
  
        var self = this;
  
        return new Promise((resolve, reject) => {
  
          //ffprobe -i /myfile.mp3 -show_frames -show_entries frame=pkt_pos -of default=noprint_wrappers=1:nokey=1 -hide_banner -loglevel panic -read_intervals 20%+#1
  
          var loglevel = self.logger.isDebug() ? 'debug' : 'panic';
  
          const args = [
  
            '-hide_banner',
  
            '-loglevel', loglevel,
  
            '-show_frames',//Display information about each frame
  
            '-show_entries', 'frame=pkt_pos',// Display only information about byte position
  
            '-of', 'default=noprint_wrappers=1:nokey=1',//Don't want to print the key and the section header and footer
  
            '-read_intervals', seconds + '%+#1', //Read only 1 packet after seeking to position 01:23
  
            '-print_format', 'json',
  
            '-v', 'quiet',
  
            '-i', fpath
  
          ];
  
          const opts = {
  
            cwd: self._options.tempDir
  
          };
  
          const cb = (error, stdout) => {
  
            if (error)
  
              return reject(error);
  
            try {
  
              const outputObj = JSON.parse(stdout);
  
              return resolve(outputObj);
  
            } catch (ex) {
  
              self.logger.error("seek failed %s", ex);
  
              return reject(ex);
  
            }
  
          };
  
          cp.execFile('ffprobe', args, opts, cb)
  
            .on('error', reject);
  
        });
  
      }//seek

  So to seek to a specified startTime position in seconds you do

  seek(path,startTime)

  and then you will get the equivalent in bytes looking at the packet of the first frames in frames like :

  position  = function() {
  
        if(this.raw.frames) {
  
          if(this.raw.frames.length>0) {// get first stream ref
  
            if(this.raw.frames[0].pkt_pos) {// get first stream ref
  
              return this.raw.frames[0].pkt_pos;
  
            }
  
          }
  
        }
  
        return '';
  
      }//position

  So, when doing seek on a mp3 file it works ok and the range query is

  rangeBytes bytes=80685-8000685 {
  
    "url": "",
  
    "path": "",
  
    "raw": {
  
      "frames": [
  
        {
  
          "pkt_pos": "80685"
  
        }
  
      ]
  
    }
  
  } {
  
    "url": "",
  
    "path": "",
  
    "raw": {
  
      "frames": [
  
        {
  
          "pkt_pos": "8000685"
  
        }
  
      ]
  
    }
  
  }

  the problem is that when I use this on a wave file, the resulting range query for the wave file :

  rangeBytes bytes=768058-76800058 {
  
    "url": "",
  
    "path": "",
  
    "raw": {
  
      "frames": [
  
        {
  
          "pkt_pos": "768058"
  
        }
  
      ]
  
    }
  
  } {
  
    "url": "",
  
    "path": "",
  
    "raw": {
  
      "frames": [
  
        {
  
          "pkt_pos": "76800058"
  
        }
  
      ]
  
    }
  
  }

  will not work in the standard HTML5 audio player.

  NOTE
  The ffprobe command line command that I’m using with the wrapper above was :

  ffprobe -i /myfile.mp3 -show_frames -show_entries frame=pkt_pos -of default=noprint_wrappers=1:nokey=1 -hide_banner -loglevel panic -read_intervals 20%+#1

  my guess is if this applies to both mp3 and wave files.