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• Why when using ffmpeg to create in real time avi video file from images the avi file is playing with purple noisy color ?

  30 juin 2015, par Brubaker Haim

  This is my Ffmpeg class i did some time ago

  using System;
  
  using System.Windows.Forms;
  
  using System.Collections.Generic;
  
  using System.Linq;
  
  using System.Text;
  
  using System.Threading.Tasks;
  
  using System.Drawing;
  
  using System.IO.Pipes;
  
  using System.Runtime.InteropServices;
  
  using System.Diagnostics;
  
  using System.IO;
  
  using DannyGeneral;
  
  
  
  namespace Manager
  
  {
  
      class Ffmpeg
  
      {
  
          NamedPipeServerStream p;
  
          String pipename = "mytestpipe";
  
          System.Diagnostics.Process process;
  
          string ffmpegFileName = "ffmpeg.exe";
  
          string workingDirectory;
  
  
  
          public Ffmpeg()
  
          {
  
              workingDirectory = Path.GetDirectoryName(Application.ExecutablePath);
  
              Logger.Write("workingDirectory: " + workingDirectory);
  
              if (!Directory.Exists(workingDirectory))
  
              {
  
                  Directory.CreateDirectory(workingDirectory);
  
              }
  
              ffmpegFileName = Path.Combine(workingDirectory, ffmpegFileName);
  
              Logger.Write("FfmpegFilename: " + ffmpegFileName);
  
          }
  
  
  
          public void Start(string pathFileName, int BitmapRate)
  
          {
  
              try
  
              {
  
  
  
                  string outPath = pathFileName;
  
                  p = new NamedPipeServerStream(pipename, PipeDirection.Out, 1, PipeTransmissionMode.Byte);
  
  
  
                  ProcessStartInfo psi = new ProcessStartInfo();
  
                  psi.WindowStyle = ProcessWindowStyle.Hidden;
  
                  psi.UseShellExecute = false;
  
                  psi.CreateNoWindow = false;
  
                  psi.FileName = ffmpegFileName;
  
                  psi.WorkingDirectory = workingDirectory;
  
                  psi.Arguments = @"-f rawvideo -pix_fmt yuv420p -video_size 1920x1080 -i \\.\pipe\mytestpipe -map 0 -c:v mpeg4 -r " + BitmapRate + " " + outPath;
  
                  process = Process.Start(psi);
  
                  process.EnableRaisingEvents = false;
  
                  psi.RedirectStandardError = true;
  
                  p.WaitForConnection();
  
              }
  
              catch (Exception err)
  
              {
  
                  Logger.Write("Exception Error: " + err.ToString());
  
              }
  
          }
  
  
  
          public void PushFrame(Bitmap bmp)
  
          {
  
              try
  
              {
  
                  int length;
  
                  // Lock the bitmap's bits.
  
                  //bmp = new Bitmap(1920, 1080);
  
                  Rectangle rect = new Rectangle(0, 0, bmp.Width, bmp.Height);
  
                  //Rectangle rect = new Rectangle(0, 0, 1280, 720);
  
                  System.Drawing.Imaging.BitmapData bmpData =
  
                      bmp.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadOnly,
  
                      bmp.PixelFormat);
  
  
  
                  int absStride = Math.Abs(bmpData.Stride);
  
                  // Get the address of the first line.
  
                  IntPtr ptr = bmpData.Scan0;
  
  
  
                  // Declare an array to hold the bytes of the bitmap.
  
                  //length = 3 * bmp.Width * bmp.Height;
  
                  length = absStride * bmpData.Height;
  
                  byte[] rgbValues = new byte[length];
  
  
  
                  //Marshal.Copy(ptr, rgbValues, 0, length);
  
                  int j = bmp.Height - 1;
  
                  for (int i = 0; i < bmp.Height; i++)
  
                  {
  
                      IntPtr pointer = new IntPtr(bmpData.Scan0.ToInt32() + (bmpData.Stride * j));
  
                      System.Runtime.InteropServices.Marshal.Copy(pointer, rgbValues, absStride * (bmp.Height - i - 1), absStride);
  
                      j--;
  
                  }
  
                  p.Write(rgbValues, 0, length);
  
                  bmp.UnlockBits(bmpData);
  
              }
  
              catch(Exception err)
  
              {
  
                  Logger.Write("Error: " + err.ToString());
  
              }
  
  
  
          }
  
  
  
          public void Close()
  
          {
  
              p.Close();
  
          }
  
      }
  
  }

  And i’m using it in form1 in a button click event :

  private void button1_Click(object sender, EventArgs e)
  
          {
  
              timer1.Start();
  
          }

  the directroy screenshots is where i’m taking a screenshot every 100ms in the timer1 tick event :

      ScreenShot shot = new ScreenShot();
  
      public static int counter = 0;
  
      private void timer1_Tick(object sender, EventArgs e)
  
      {
  
          counter++;
  
          shot.GetScreenShot(@"e:\screenshots\", "screenshot");
  
          if (counter == 1200)
  
          {
  
              timer1.Stop();
  
          }
  
      }

  I’m calling the method PushFrame from inside the ScreenShot class where i save the screenshots.

  Ffmpeg fmpeg;

  Then :

  fmpeg = new Ffmpeg();
  
  fmpeg.Start(@"e:\screenshots\test.avi", 25);

  And :

  public Bitmap GetScreenShot(string folder, string name)
  
      {
  
          _screenShot = new Bitmap(GetScreen());
  
          System.GC.Collect();
  
          System.GC.WaitForPendingFinalizers();
  
          string ingName = folder + name + Elgato_Video_Capture.counter.ToString("D6") + ".bmp";
  
          _screenShot.Save(ingName);
  
          fmpeg.PushFrame(_screenShot);
  
          _screenShot.Dispose();
  
  
  
          return _screenShot;
  
      }

  All the images on the hard disk are fine i can edit/open them and watch them no problems.
  They are also same size.

  The result in the end is one big avi file 1.08 GB size.
  But when i play it i see many windows running inside very fast and all painted with noisy purple color.

  Here a screenshot from the video file when playing it :

  avi file playing screenshot

  I think the problem is somewhere in the Ffmpeg class where i give parameters to the ffmpeg.exe

  psi.Arguments = @"-f rawvideo -pix_fmt yuv420p -video_size 1920x1080 -i \\.\pipe\mytestpipe -map 0 -c:v mpeg4 -r " + BitmapRate + " " + outPath;

  Not sure what make this avi file to look like that.

  This is the video file the result i got : https://www.youtube.com/watch?v=fdxPus-Xv1k&feature=youtu.be

• With ffmpeg, how can I combine a video stream with 2 audio streams, with only 1 of the audio streams playing at a specific time

  5 juin 2023, par tiagosilva

  I have a video and 2 audio streams, in 2 different languages (one live, the other a dubbed version, all streams have the same lenght).

  


  I want to combine these into one final output, but I don't want to ever mix both. I want to tell ffmpeg to use audio stream 1 up to minute 10, and use audio stream 2 after that.

  


  How can I achieve this ? I figure I might need amix, but that just mixes the audiostreams and makes them simultaneous, I only want one audio stream at a time.

  


  Bonus points if it can be done without re-encoding

  


• When decoding video with ffmpeg and playing the decoded audio data with SDL2, it's all noise [closed]

  18 février, par jodan feng

  it is the code in the main thread

  


  int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Ffplay f;
    f.start();
    return a.exec();
}


  


  Ffplay is the thread that decode the video and play it

  


  class Ffplay : public QThread
{
   Q_OBJECT
public:
    Ffplay();
    protected:
      void run() override;
public:
    AVFormatContext* format2;
    Thread2 t2;
};
Ffplay::Ffplay() {}

void Ffplay::run(){
    format2=avformat_alloc_context();
    avformat_open_input(&format2,"c:/Qt/project/player/movie.mp4",NULL,NULL);
    avformat_find_stream_info(format2,NULL);
    t2.format=format2;
    t2.start();
}


  


  Thread2 is the thread that decoed the audio part and play it

  


  class Thread2 : public QThread
{
    Q_OBJECT
public:
    Thread2();
protected:
    void run() override;
public:
    AVFormatContext* format;
    AVCodecContext* codec;
    const AVCodec* c;
    AVPacket* packet;
    AVFrame* frame;
    SwrContext* s;
    FILE* f;
    FILE* f2;

};
Thread2::Thread2() {}

struct Sound
{
    Uint8* data;
    Uint32 position=0;
    Uint32 len;
};

Sound* d=new Sound;

void write(void* userdata,Uint8* stream,int len){
    SDL_memset(stream,0,len);
    int size2=std::min((Uint32)len,d->len-d->position);
    SDL_memcpy(stream,d->data+d->position,size2);
    d->position=d->position+size2;
}


void Thread2::run(){
    int index=-1;
    for(unsigned int i=0;inb_streams;i++){
        if(format->streams[i]->codecpar->codec_type==AVMEDIA_TYPE_AUDIO){
            index=i;
            break;
        }
    }
    c=avcodec_find_decoder(format->streams[index]->codecpar->codec_id);
    codec=avcodec_alloc_context3(c);
    avcodec_parameters_to_context(codec,format->streams[index]->codecpar);
    avcodec_open2(codec,c,NULL);
    packet=av_packet_alloc();
    frame=av_frame_alloc();
    s=swr_alloc();
    swr_alloc_set_opts2(&s,&codec->ch_layout,AV_SAMPLE_FMT_S16,codec->sample_rate,&codec->ch_layout,codec->sample_fmt,codec->sample_rate,0,NULL);
    swr_init(s);
    f=fopen("yinpin","wb");
    uint8_t* buff=(uint8_t*)av_malloc(2*1024*4);  
    while(av_read_frame(format,packet)==0){
        if(packet->stream_index==1){
            avcodec_send_packet(codec,packet);
            while(avcodec_receive_frame(codec,frame)>=0){
                swr_convert(s,&buff,2*1024*2*2,(const uint8_t **)frame->data,frame->nb_samples);
                int size=av_samples_get_buffer_size(NULL,2,frame->nb_samples,AV_SAMPLE_FMT_S16,1);
                fwrite(buff,1,size,f);
            }
        }
    }


    SDL_Init(SDL_INIT_AUDIO);
    SDL_AudioSpec spec;
    spec.freq=48000;
    spec.format=AUDIO_S16;
    spec.channels=2;
    spec.samples=1024;
    spec.callback=write;
    SDL_OpenAudio(&spec,NULL);
    SDL_PauseAudio(0);
    f2=fopen("yinpin","rb");
    uint8_t* buff2=(uint8_t*)av_malloc(2*2*1024*2);
    size_t size=10;
    while(size>0){
        size=fread(buff2,1,2*2*1024*2,f2);
        d->data=buff2;
        d->len=(Uint32)size;
    }
}


  


  After the program is run, the sound played is all noise, which makes me a little confused because I don't know whether it is a decoding problem or a problem with SDL2 audio playback. Is there any troubleshooting method ? Has anyone figured out the source of the problem ?