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• Write audio packet to file using ffmpeg

  27 février 2017, par iamyz

  I am trying to write audio packet to file using ffmpeg. The source device sending the packet after some interval. e.g.

  First packet has a time stamp 00:00:00 
  
  Second packet has a time stamp 00:00:00.5000000
  
  Third packet has a time stamp 00:00:01
  
  And so on...

  Means two packet per second.

  I want to encode those packets and write to a file.

  I am referring the Ffmpeg example from link Muxing.c

  While encoding and writing there is no error. But output file has only 2 sec audio duration and speed is also super fast.

  The video frames are proper according the settings.

  I think the problem is related to calculation of pts, dts and duration of packet.

  How should I calculate proper values for pts, dts and duration. Or is this problem related to other thing ?

  Code :

  void AudioWriter::WriteAudioChunk(IntPtr chunk, int lenght, TimeSpan timestamp)
  
  {
  
      int buffer_size = av_samples_get_buffer_size(NULL, outputStream->tmp_frame->channels, outputStream->tmp_frame->nb_samples,  outputStream->AudioStream->codec->sample_fmt, 0);
  
  
  
      uint8_t *audioData = reinterpret_cast(static_cast(chunk));
  
      int ret = avcodec_fill_audio_frame(outputStream->tmp_frame,outputStream->Channels, outputStream->AudioStream->codec->sample_fmt, audioData, buffer_size, 1);
  
  
  
      if (!ret)
  
         throw gcnew System::IO::IOException("A audio file was not opened yet.");
  
  
  
      write_audio_frame(outputStream->FormatContext, outputStream, audioData);
  
  }
  
  
  
  
  
  static int write_audio_frame(AVFormatContext *oc, AudioWriterData^ ost, uint8_t *audioData)
  
  {
  
         AVCodecContext *c;
  
         AVPacket pkt = { 0 };
  
         int ret;
  
         int got_packet;
  
         int dst_nb_samples;
  
  
  
         av_init_packet(&pkt);
  
         c = ost->AudioStream->codec;
  
  
  
         AVFrame *frame = ost->tmp_frame;
  
  
  
        if (frame)
  
        {
  
            dst_nb_samples = av_rescale_rnd(swr_get_delay(ost->swr_ctx, c->sample_rate) + frame->nb_samples, c->sample_rate, c->sample_rate, AV_ROUND_UP);
  
            if (dst_nb_samples != frame->nb_samples)
  
              throw gcnew Exception("dst_nb_samples != frame->nb_samples");
  
  
  
            ret = av_frame_make_writable(ost->AudioFrame);
  
            if (ret < 0)
  
               throw gcnew Exception("Unable to make writable.");
  
  
  
            ret = swr_convert(ost->swr_ctx, ost->AudioFrame->data, dst_nb_samples, (const uint8_t **)frame->data, frame->nb_samples);
  
            if (ret < 0) 
  
              throw gcnew Exception("Unable to convert to destination format.");
  
  
  
            frame = ost->AudioFrame;
  
  
  
            AVRational timebase = { 1, c->sample_rate };
  
            frame->pts = av_rescale_q(ost->samples_count, timebase, c->time_base);
  
            ost->samples_count += dst_nb_samples;
  
        }
  
  
  
        ret = avcodec_encode_audio2(c, &pkt, frame, &got_packet);
  
        if (ret < 0) 
  
          throw gcnew Exception("Error encoding audio frame.");
  
  
  
        if (got_packet)
  
        {
  
          ret = write_frame(oc, &c->time_base, ost->AudioStream, &pkt);
  
          if (ret < 0)
  
              throw gcnew Exception("Audio is not written.");
  
        }
  
        else
  
           throw gcnew Exception("Audio packet encode failed.");
  
  
  
        return (ost->AudioFrame || got_packet) ? 0 : 1;
  
  }
  
  
  
  static int write_frame(AVFormatContext *fmt_ctx, const AVRational *time_base, AVStream *st, AVPacket *pkt)
  
  {
  
      av_packet_rescale_ts(pkt, *time_base, st->time_base);
  
      pkt->stream_index = st->index;
  
      return av_interleaved_write_frame(fmt_ctx, pkt);
  
  }

• What codec/format to use for fastest possible decoding ?

  2 mars 2017, par JT J

  I’m using an ffmpeg script (in Windows) that extracts all the keyframes from a video and pastes them into a folder. I’ve made sure that my drive speed, CPU, and RAM are not causing a bottleneck.

  The quality of the video is actually not important at all in this case. I need to encode the video that the script extracts frames from so that it has the fastest possible decoding speed. File size and quality are not important, only read speed. The video does not have audio. What would work best for me ?

  If it matters, here’s the script I’m working with :

  ffmpeg -i input.mp4 -vf "select=eq(pict_type\,I)" -vsync 1 %%3d.bmp

  Sorry if sound like I don’t know what I’m talking about, this is not a topic I am super familiar with. I appreciate your help !

• Android : how to film a video before extracting its audio

  20 février 2017, par MrOrgon

  Despite many searches, I haven’t been able to develop a Android prototype able to film a video before extracting its audio as .wav in a separate activity.

  I have developed so far a simple filming activity which relies on Android’s Camera application. My strategty was to put the video’s Uri as Extra to the next activity, before using FFMPEG, but I can’t make the transition between Uri and FFMPEG. Indeed, I’m a fresh Android Studio beginner, so I still am not sure about what concept to use.

  Here’s my code for the video recording activity.

  import android.net.Uri;
  
  import android.os.Build;
  
  import android.os.Bundle;
  
  import android.provider.MediaStore;
  
  import android.widget.Toast;
  
  import android.widget.VideoView;
  
  
  
  import java.io.File;
  
  import java.io.FileInputStream;
  
  import java.io.FileOutputStream;
  
  import java.io.IOException; 
  
  import java.nio.channels.FileChannel;
  
  
  
  import static java.security.AccessController.getContext;
  
  
  
  
  
  public class RecordActivity extends Activity{
  
  
  
  static final int REQUEST_VIDEO_CAPTURE = 0;
  
  
  
  VideoView mVideoView = null;
  
  Uri videoUri = null;
  
  
  
  @Override
  
  public void onCreate(Bundle savedInstanceState) {
  
      super.onCreate(savedInstanceState);
  
      mVideoView = (VideoView) findViewById(R.id.videoVieww);
  
      setContentView(R.layout.activity_record);
  
  
  
      Intent takeVideoIntent = new Intent(MediaStore.ACTION_VIDEO_CAPTURE);
  
  
  
      Toast.makeText(RecordActivity.this,         String.valueOf(Build.VERSION.SDK_INT) , Toast.LENGTH_SHORT).show();
  
  
  
      takeVideoIntent.putExtra(MediaStore.EXTRA_OUTPUT, videoUri);
  
      if (takeVideoIntent.resolveActivity(getPackageManager()) != null) {
  
          startActivityForResult(takeVideoIntent, REQUEST_VIDEO_CAPTURE);
  
      }
  
  
  
  }
  
  
  
  
  
      @Override
  
      protected void onActivityResult(int requestCode, int resultCode, Intent intent) {
  
          if (requestCode == REQUEST_VIDEO_CAPTURE && resultCode == RESULT_OK) {
  
              videoUri = intent.getData();
  
  
  
              Intent intentForFilterActivity = new Intent(RecordActivity.this, FilterActivity.class);
  
              intentForFilterActivity.putExtra("VideoToFilter", videoUri.getPath());
  
              startActivity(intentForFilterActivity);
  
  
  
          }
  
      }
  
  }

  Here’s the the code for the audio extraction activity. It is called "FilterActivity", as its final aim is to filter outdoor noise using additional functions. I’m using WritingMinds’ implementation of FFMPEG.
  https://github.com/WritingMinds/ffmpeg-android-java

   import android.app.Activity;
  
   import android.content.Intent;
  
   import android.os.Bundle;
  
   import android.test.ActivityUnitTestCase;
  
   import android.widget.Toast;
  
  
  
   import com.github.hiteshsondhi88.libffmpeg.ExecuteBinaryResponseHandler;
  
   import com.github.hiteshsondhi88.libffmpeg.FFmpeg;
  
   import  com.github.hiteshsondhi88.libffmpeg.exceptions.FFmpegCommandAlreadyRunningException;
  
  
  
  
  
  
  
  public class FilterActivity extends Activity {
  
  
  
  @Override
  
  public void onCreate(Bundle savedInstanceState) {
  
  
  
      super.onCreate(savedInstanceState);
  
      setContentView(R.layout.activity_filter);
  
  
  
      Intent intentVideo = getIntent();
  
      String pathIn = intentVideo.getStringExtra("VideoToFilter");
  
  
  
      FFmpeg ffmpeg = FFmpeg.getInstance(FilterActivity.this);
  
      try {
  
          String[] cmdExtract = {"-i " + pathIn + " extracted.wav"};
  
          ffmpeg.execute(cmdExtract, new ExecuteBinaryResponseHandler() {
  
  
  
              @Override
  
              public void onStart() {}
  
  
  
              @Override
  
              public void onProgress(String message) {}
  
  
  
              @Override
  
              public void onFailure(String message) {
  
                  Toast.makeText(FilterActivity.this, "Failure !", Toast.LENGTH_SHORT).show();
  
              }
  
  
  
              @Override
  
              public void onSuccess(String message) {}
  
  
  
              @Override
  
              public void onFinish() {}
  
          });
  
      } catch (FFmpegCommandAlreadyRunningException e) {
  
      }
  
  }
  
  
  
  
  
  }

  and I always get the "Failure !" message.

  Some parts of the code may look extremely bad. As as written previously, I’m a real Android Studio beginner.

  Do you have any correction that could work ? Or even just a strategy ?

  Thank you in advance !