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• How to decode a H.264 frame on iOS by hardware decoding ?

  23 septembre 2015, par ChihHao

  I have been used ffmpeg to decode every single frame that I received from my ip cam. The brief code looks like this :

  -(void) decodeFrame:(unsigned char *)frameData frameSize:(int)frameSize{
  
     AVFrame frame;
  
     AVPicture picture;
  
     AVPacket pkt;
  
     AVCodecContext *context;
  
     pkt.data = frameData;
  
     pat.size = frameSize;
  
     avcodec_get_frame_defaults(&frame);
  
     avpicture_alloc(&picture, PIX_FMT_RGB24, targetWidth, targetHeight);
  
     avcodec_decode_video2(&context, &frame, &got_picture, &pkt);
  
  }

  The code woks fine, but it’s software decoding. I want to enhance the decoding performance by hardware decoding. After lots of research, I know it may be achieved by AVFoundation framework.
  The AVAssetReader class may help, but I can’t figure out what’s the next.Could anyone points out the following steps for me ? Any help would be appreciated.

• Using ffmpeg to convert voice recording captured by HTML5

  8 juillet 2014, par user3789242

  I’m building an HTML5 voice recording software with visualizer.I want the user when recording the voice, and after uploading the file as wave in a blob (server-side), the user should be able to select the audio format of that file using ffmpeg. what I Have achieved so far is uploading the file as wave.what I still want to do is :

  • On the server
  • side pick your preferable web programming framework
  • The web programming framework accepts the upload and stores the file on the server
  • The web programming framework runs a ffmpeg (command line) which processes the file
  • The user can download the processed file

  here is my code so far :

  // variables
  
  var leftchannel = [];
  
  var rightchannel = [];
  
  var recorder = null;
  
  var recording = false;
  
  var recordingLength = 0;
  
  var volume = null;
  
  var audioInput = null;
  
  var sampleRate = 44100;
  
  var audioContext = null;
  
  var context = null;
  
  var outputString;
  
  
  
  
  
  
  
  if (!navigator.getUserMedia)
  
      navigator.getUserMedia = navigator.getUserMedia ||
  
      navigator.webkitGetUserMedia ||
  
      navigator.mozGetUserMedia ||
  
      navigator.msGetUserMedia;
  
  
  
  if (navigator.getUserMedia) {
  
      navigator.getUserMedia({
  
          audio: true
  
      }, success, function (e) {
  
          alert('Error capturing audio.');
  
      });
  
  } else alert('getUserMedia not supported in this browser.');
  
  
  
  
  
  
  
  function getVal(value) {
  
  
  
      // if R is pressed, we start recording
  
      if (value == "record") {
  
          recording = true;
  
          // reset the buffers for the new recording
  
          leftchannel.length = rightchannel.length = 0;
  
          recordingLength = 0;
  
          document.getElementById('output').innerHTML = "Recording now...";
  
  
  
          // if S is pressed, we stop the recording and package the WAV file
  
      } else if (value == "stop") {
  
  
  
          // we stop recording
  
          recording = false;
  
          document.getElementById('output').innerHTML = "Building wav file...";
  
  
  
          // we flat the left and right channels down
  
          var leftBuffer = mergeBuffers(leftchannel, recordingLength);
  
          var rightBuffer = mergeBuffers(rightchannel, recordingLength);
  
          // we interleave both channels together
  
          var interleaved = interleave(leftBuffer, rightBuffer);
  
  
  
  
  
  
  
          var buffer = new ArrayBuffer(44 + interleaved.length * 2);
  
          var view = new DataView(buffer);
  
  
  
          // RIFF chunk descriptor
  
          writeUTFBytes(view, 0, 'RIFF');
  
          view.setUint32(4, 44 + interleaved.length * 2, true);
  
          writeUTFBytes(view, 8, 'WAVE');
  
          // FMT sub-chunk
  
          writeUTFBytes(view, 12, 'fmt ');
  
          view.setUint32(16, 16, true);
  
          view.setUint16(20, 1, true);
  
          // stereo (2 channels)
  
          view.setUint16(22, 2, true);
  
          view.setUint32(24, sampleRate, true);
  
          view.setUint32(28, sampleRate * 4, true);
  
          view.setUint16(32, 4, true);
  
          view.setUint16(34, 16, true);
  
          // data sub-chunk
  
          writeUTFBytes(view, 36, 'data');
  
          view.setUint32(40, interleaved.length * 2, true);
  
  
  
  
  
          var lng = interleaved.length;
  
          var index = 44;
  
          var volume = 1;
  
          for (var i = 0; i < lng; i++) {
  
              view.setInt16(index, interleaved[i] * (0x7FFF * volume), true);
  
              index += 2;
  
          }
  
  
  
          var blob = new Blob([view], {
  
              type: 'audio/wav'
  
          });
  
  
  
          // let's save it locally
  
  
  
          document.getElementById('output').innerHTML = 'Handing off the file now...';
  
          var url = (window.URL || window.webkitURL).createObjectURL(blob);
  
  
  
          var li = document.createElement('li');
  
          var au = document.createElement('audio');
  
          var hf = document.createElement('a');
  
  
  
          au.controls = true;
  
          au.src = url;
  
          hf.href = url;
  
          hf.download = 'audio_recording_' + new Date().getTime() + '.wav';
  
          hf.innerHTML = hf.download;
  
          li.appendChild(au);
  
          li.appendChild(hf);
  
          recordingList.appendChild(li);
  
  
  
      }
  
  }
  
  
  
  
  
  function success(e) {
  
  
  
      audioContext = window.AudioContext || window.webkitAudioContext;
  
      context = new audioContext();
  
  
  
  
  
      volume = context.createGain();
  
  
  
      // creates an audio node from the microphone incoming stream(source)
  
      source = context.createMediaStreamSource(e);
  
  
  
      // connect the stream(source) to the gain node
  
      source.connect(volume);
  
  
  
      var bufferSize = 2048;
  
  
  
      recorder = context.createScriptProcessor(bufferSize, 2, 2);
  
  
  
      //node for the visualizer
  
      analyser = context.createAnalyser();
  
      analyser.smoothingTimeConstant = 0.3;
  
      analyser.fftSize = 512;
  
  
  
      splitter = context.createChannelSplitter();
  
      //when recording happens
  
      recorder.onaudioprocess = function (e) {
  
  
  
          if (!recording) return;
  
          var left = e.inputBuffer.getChannelData(0);
  
          var right = e.inputBuffer.getChannelData(1);
  
  
  
          leftchannel.push(new Float32Array(left));
  
          rightchannel.push(new Float32Array(right));
  
          recordingLength += bufferSize;
  
  
  
          // get the average for the first channel
  
          var array = new Uint8Array(analyser.frequencyBinCount);
  
          analyser.getByteFrequencyData(array);
  
  
  
          var c = document.getElementById("myCanvas");
  
          var ctx = c.getContext("2d");
  
          // clear the current state
  
          ctx.clearRect(0, 0, 1000, 325);
  
          var gradient = ctx.createLinearGradient(0, 0, 0, 300);
  
          gradient.addColorStop(1, '#000000');
  
          gradient.addColorStop(0.75, '#ff0000');
  
          gradient.addColorStop(0.25, '#ffff00');
  
          gradient.addColorStop(0, '#ffffff');
  
          // set the fill style
  
          ctx.fillStyle = gradient;
  
          drawSpectrum(array);
  
  
  
          function drawSpectrum(array) {
  
              for (var i = 0; i < (array.length); i++) {
  
                  var value = array[i];
  
                  ctx.fillRect(i * 5, 325 - value, 3, 325);
  
              }
  
  
  
          }
  
      }
  
  
  
      function getAverageVolume(array) {
  
          var values = 0;
  
          var average;
  
  
  
          var length = array.length;
  
  
  
          // get all the frequency amplitudes
  
          for (var i = 0; i < length; i++) {
  
              values += array[i];
  
          }
  
  
  
          average = values / length;
  
          return average;
  
      }
  
  
  
      // we connect the recorder(node to destination(speakers))
  
      volume.connect(splitter);
  
      splitter.connect(analyser, 0, 0);
  
  
  
      analyser.connect(recorder);
  
      recorder.connect(context.destination);
  
  
  
  }
  
  
  
  
  
  
  
  
  
  function mergeBuffers(channelBuffer, recordingLength) {
  
      var result = new Float32Array(recordingLength);
  
      var offset = 0;
  
      var lng = channelBuffer.length;
  
      for (var i = 0; i < lng; i++) {
  
          var buffer = channelBuffer[i];
  
          result.set(buffer, offset);
  
          offset += buffer.length;
  
      }
  
      return result;
  
  }
  
  
  
  function interleave(leftChannel, rightChannel) {
  
      var length = leftChannel.length + rightChannel.length;
  
      var result = new Float32Array(length);
  
  
  
      var inputIndex = 0;
  
  
  
      for (var index = 0; index < length;) {
  
          result[index++] = leftChannel[inputIndex];
  
          result[index++] = rightChannel[inputIndex];
  
          inputIndex++;
  
      }
  
      return result;
  
  }
  
  
  
  
  
  function writeUTFBytes(view, offset, string) {
  
      var lng = string.length;
  
      for (var i = 0; i < lng; i++) {
  
  
  
          view.setUint8(offset + i, string.charCodeAt(i));
  
      }
  
  }

• How to save changes in video file in Ffmpeg C++ ?

  16 avril 2021, par TheSofya

  How to save changes in video file in Ffmpeg C++ ? Do we need encoder ? How to use avcodec_encode_video2 functions ?

  


  while (av_read_frame(pFormatCtx, &packet) >= 0)
    {

        if (packet.stream_index == videoStream) {
            avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet); 
            if (frameFinished) {
                sws_scale(sws_ctx, (uint8_t const* const*)pFrame->data,
                    pFrame->linesize, 0, pCodecCtx->height,
                    pFrameRGB->data, pFrameRGB->linesize);

                if (i == secretframe) {
                    //Here we change pixels
                    hidetext(pFrameRGB, pCodecCtx->width, pCodecCtx->height, secretframe);
                    //unhidetext(pFrameRGB, pCodecCtx->width, pCodecCtx->height, secretframe); 

                    std::cout << "\n\n" << i << "\n\n";
                }
                if (i > secretframe) { 
                break; 
                }
                i++;
            }
        }