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• Is there any way to change file FPS in javascript browser or prepare wav conventer to 60FPS videos ?

  16 novembre 2020, par SZtyro

  I'm making web application which stores short audio files that have been cut from large video files. User uploads .mp4 file, chooses sound length and here's a little trick. Cutting audio can only be done in backend (correct me if I'm wrong) and sending 700MB data is not good option, so I use code below to decode audio data from .mp4 and then I send it with start and stop params. Backend (Node.js) use's FFMPEG to cut audio and save's it.

  


  This part works, but i realised that decoded audio from 60FPS video doesn't sound good (not terrible but totally useless in my app). My goal is to avoid third party, especially desktop, apps (like audacity) and allow user to cut revelant part of audio from any mp4 video. Is there any way to convert 60FPS video to 30FPS video (ArrayBuffer) in browser and then decode audio ?

  


        fileInput.onchange = event => {
      this.file = event.target["files"][0];
      //.mp4 file
      this.fileURL = URL.createObjectURL(this.file)

      let baseAudioContext = new AudioContext();
      this.file.arrayBuffer().then(buff => {

        baseAudioContext.decodeAudioData(buff,
          success => {
            console.log(success)
            this.bufferToWave(success, 0, success.length);
          },
          err => console.log(err));
      })
    }

  bufferToWave(abuffer, offset, len) {

    var numOfChan = abuffer.numberOfChannels,
      length = len * numOfChan * 2 + 44,
      buffer = new ArrayBuffer(length),
      view = new DataView(buffer),
      channels = [], i, sample,
      pos = 0;

    // write WAVE header
    setUint32(0x46464952);                         // "RIFF"
    setUint32(length - 8);                         // file length - 8
    setUint32(0x45564157);                         // "WAVE"

    setUint32(0x20746d66);                         // "fmt " chunk
    setUint32(16);                                 // length = 16
    setUint16(1);                                  // PCM (uncompressed)
    setUint16(numOfChan);
    setUint32(abuffer.sampleRate);
    setUint32(abuffer.sampleRate * 2 * numOfChan); // avg. bytes/sec
    setUint16(numOfChan * 2);                      // block-align
    setUint16(16);                                 // 16-bit (hardcoded in this demo)

    setUint32(0x61746164);                         // "data" - chunk
    setUint32(length - pos - 4);                   // chunk length

    // write interleaved data
    for (i = 0; i < abuffer.numberOfChannels; i++)
      channels.push(abuffer.getChannelData(i));

    while (pos < length) {
      for (i = 0; i < numOfChan; i++) {             // interleave channels
        sample = Math.max(-1, Math.min(1, channels[i][offset])); // clamp
        sample = (0.5 + sample < 0 ? sample * 32768 : sample * 32767) | 0; // scale to 16-bit signed int
        view.setInt16(pos, sample, true);          // update data chunk
        pos += 2;
      }
      offset++                                     // next source sample
    }

    // create Blob
    //return (URL || webkitURL).createObjectURL(new Blob([buffer], { type: "audio/wav" }));
    var u = (URL || webkitURL).createObjectURL(new Blob([buffer], { type: "audio/wav" }));

    //temporary part
    //downloading file to check quality
    //in this part sound is already broken, no need to show backend code
    const a = document.createElement('a');
    a.style.display = 'none';
    a.href = u;
    a.download = name;
    document.body.appendChild(a);
    a.click();



    function setUint16(data) {
      view.setUint16(pos, data, true);
      pos += 2;
    }

    function setUint32(data) {
      view.setUint32(pos, data, true);
      pos += 4;
    }
  }


  


• FFMPEG - subtitles not showing for the full duration of video

  26 juin 2023, par Caio Maia

  I could not archive the following :

  


  

  1. Have images loaded from a textfile to create a slideshow.

  


  2. Have a background music with volume control.

  


  3. Have my voice.mp3 over the bg music.

  


  4. Have subtitles in the ass format.

  


  5. Have a text shown with drawtext in the full duration of video.

  


  6. in only one command, if possible.

  


  


  The command I tryed is :

  


  ffmpeg.exe -f concat -i images.txt -i bg_music.m4a -i voice.mp3 -filter_complex "[0:v]drawtext=fontfile='fonte.TTF':fontsize=20:fontcolor=white:text='Imagens da internet':x=w-tw-10:y=h-th-10,[0]overlay=10:10,ass=subtitles.txt[out],[1]volume=0.3[a1];[2]volume=2[a2];[a1][a2]amix=inputs=2:duration=shortest[aud]" -map "[out]" -map "[aud]":a -pix_fmt yuv420p -c:v libx264 -c:s mov_text -r 30 -y out.mp4


  


  It works but not for subtitles that are showing only after the first image of th slideshow appears.

  


  the content of images.txt is :

  


  file 'image1.png'
duration 20
file 'image2.png'
duration 5
file 'image3.png'
duration 5


  


  the content of subtitles.txt is

  


  Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:01.00,0:00:06.00,Default,,0,0,0,,Subscribe!
Dialogue: 0,0:00:07.00,0:00:16.00,Default2,,0,0,0,,Like!
Dialogue: 0,0:00:17.00,0:00:26.00,Default,,0,0,0,,Share!


  


  The problem is that only the "Share !" text is shown.

  


• How to run ffmpeg with hardware encoding when using —filter_complex to hardcode subtitles ? [closed]

  28 avril 2024, par user2006141

  I'm converting MKV files and hardcoding subtitles into MP4 format. I have over 100 files and want to speed the process up by enabling hardware encoding. I am able to hardware encode without hardcoding the subtitles via —filter_complex but as soon as I apply the filter it errors out.

  


  Here is my command line that works perfectly fine.

  


  ffmpeg -i input.mkv -filter_complex "[0:v:0]subtitles='input.mkv':si=0[v]" -map "[v]" -map 0:a:1 -c:a copy -map_chapters -1 "output.mp4"

  


  Here is my command line that works with hardware encoding without —filter_complex

  


  ffmpeg -hwaccel cuda -hwaccel_output_format cuda -i input.mkv -c:v hevc_nvenc -map 0:a:1 -c:a copy -map_chapters -1 "output.mp4"

  


  What I need to do is enable hardware encoding with —filter_complex, So I tried this command

  


  ffmpeg -hwaccel cuda -hwaccel_output_format cuda -i input.mkv -filter_complex "[0:v:0]subtitles='input.mkv':si=0[v]" -map "[v]" -c:v hevc_nvenc -map 0:a:1 -c:a copy -map_chapters -1 "output.mp4"

  


  I get this error

  


  Impossible to convert between the formats supported by the filter 'graph 0 input from stream 0:0' and the filter 'auto_scale_0'