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• Encoding frames to video with ffmpeg

  5 septembre 2017, par Mher Didaryan

  I am trying to encode a video in Unreal Engine 4 with C++. I have access to the separate frames. Below is the code which reads viewport's displayed pixels and stores in buffer.

  //Safely get render target resource.
  
  FRenderTarget* RenderTarget = TextureRenderTarget->GameThread_GetRenderTargetResource();
  
  FIntPoint Size = RenderTarget->GetSizeXY();
  
  auto ImageBytes = Size.X* Size.Y * static_cast<int32>(sizeof(FColor));
  
  TArray<uint8> RawData;
  
  RawData.AddUninitialized(ImageBytes);
  
  
  
  //Get image raw data.
  
  if (!RenderTarget->ReadPixelsPtr((FColor*)RawData.GetData()))
  
  {
  
      RawData.Empty();
  
      UE_LOG(ExportRenderTargetBPFLibrary, Error, TEXT("ExportRenderTargetAsImage: Failed to get raw data."));
  
      return false;
  
  }
  
  
  
  Buffer::getInstance().add(RawData);
  
  </uint8></int32>

  Unreal Engine has IImageWrapperModule with which you can get an image from frame, but noting for video encoding. What I want is to encode frames in real time basis for live streaming service.

  I found this post Encoding a screenshot into a video using FFMPEG which is kind of what I want, but I have problems adapting this solution for my case. The code is outdated (for example avcodec_encode_video changed to avcodec_encode_video2 with different parameters).

  Bellow is the code of encoder.

  void Compressor::DoWork()
  
  {
  
  AVCodec* codec;
  
  AVCodecContext* c = NULL;
  
  //uint8_t* outbuf;
  
  //int /*i, out_size,*/ outbuf_size;
  
  
  
  UE_LOG(LogTemp, Warning, TEXT("encoding"));
  
  
  
  codec = avcodec_find_encoder(AV_CODEC_ID_MPEG1VIDEO);            // finding the H264 encoder
  
  if (!codec) {
  
      UE_LOG(LogTemp, Warning, TEXT("codec not found"));
  
      exit(1);
  
  }
  
  else UE_LOG(LogTemp, Warning, TEXT("codec found"));
  
  
  
  c = avcodec_alloc_context3(codec);
  
  c->bit_rate = 400000;
  
  c->width = 1280;                                        // resolution must be a multiple of two (1280x720),(1900x1080),(720x480)
  
  c->height = 720;
  
  c->time_base.num = 1;                                   // framerate numerator
  
  c->time_base.den = 25;                                  // framerate denominator
  
  c->gop_size = 10;                                       // emit one intra frame every ten frames
  
  c->max_b_frames = 1;                                    // maximum number of b-frames between non b-frames
  
  c->keyint_min = 1;                                      // minimum GOP size
  
  c->i_quant_factor = (float)0.71;                        // qscale factor between P and I frames
  
  //c->b_frame_strategy = 20;                               ///// find out exactly what this does
  
  c->qcompress = (float)0.6;                              ///// find out exactly what this does
  
  c->qmin = 20;                                           // minimum quantizer
  
  c->qmax = 51;                                           // maximum quantizer
  
  c->max_qdiff = 4;                                       // maximum quantizer difference between frames
  
  c->refs = 4;                                            // number of reference frames
  
  c->trellis = 1;                                         // trellis RD Quantization
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;                           // universal pixel format for video encoding
  
  c->codec_id = AV_CODEC_ID_MPEG1VIDEO;
  
  c->codec_type = AVMEDIA_TYPE_VIDEO;
  
  
  
  if (avcodec_open2(c, codec, NULL) < 0) {
  
      UE_LOG(LogTemp, Warning, TEXT("could not open codec"));         // opening the codec
  
      //exit(1);
  
  }
  
  else UE_LOG(LogTemp, Warning, TEXT("codec oppened"));
  
  
  
  FString FinalFilename = FString("C:/Screen/sample.mpg");
  
  auto &PlatformFile = FPlatformFileManager::Get().GetPlatformFile();
  
  auto FileHandle = PlatformFile.OpenWrite(*FinalFilename, true);
  
  
  
  if (FileHandle)
  
  {
  
      delete FileHandle; // remove when ready
  
      UE_LOG(LogTemp, Warning, TEXT("file opened"));
  
      while (true)
  
      {
  
          UE_LOG(LogTemp, Warning, TEXT("removing from buffer"));
  
  
  
          int nbytes = avpicture_get_size(AV_PIX_FMT_YUV420P, c->width, c->height);                                      // allocating outbuffer
  
          uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes * sizeof(uint8_t));
  
  
  
          AVFrame* inpic = av_frame_alloc();
  
          AVFrame* outpic = av_frame_alloc();
  
  
  
          outpic->pts = (int64_t)((float)1 * (1000.0 / ((float)(c->time_base.den))) * 90);                              // setting frame pts
  
          avpicture_fill((AVPicture*)inpic, (uint8_t*)Buffer::getInstance().remove().GetData(),
  
              AV_PIX_FMT_PAL8, c->width, c->height); // fill image with input screenshot
  
          avpicture_fill((AVPicture*)outpic, outbuffer, AV_PIX_FMT_YUV420P, c->width, c->height);                        // clear output picture for buffer copy
  
          av_image_alloc(outpic->data, outpic->linesize, c->width, c->height, c->pix_fmt, 1);
  
  
  
          /* 
  
          inpic->data[0] += inpic->linesize[0]*(screenHeight-1);                                                      
  
          // flipping frame
  
          inpic->linesize[0] = -inpic->linesize[0];                                                                   
  
          // flipping frame
  
  
  
          struct SwsContext* fooContext = sws_getContext(screenWidth, screenHeight, PIX_FMT_RGB32, c->width, c->height, PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);
  
          sws_scale(fooContext, inpic->data, inpic->linesize, 0, c->height, outpic->data, outpic->linesize);          // converting frame size and format
  
  
  
          out_size = avcodec_encode_video(c, outbuf, outbuf_size, outpic);                                            
  
          // save in file
  
  
  
          */
  
  
  
      }
  
      delete FileHandle;
  
  }
  
  else
  
  {
  
      UE_LOG(LogTemp, Warning, TEXT("Can't open file"));
  
  }
  
  }

  Can someone explain flipping frame part (why it’s done ?) and how to use avcodec_encode_video2 function instead of avcodec_encode_video ?

• Delphi, TBitmap (rgb) to YCbCr colors format

  18 octobre 2019, par Alexander M.

  have a video encoding example from http://www.delphiffmpeg.com - need to convert a set of TBitmaps to YCbCr (YUV), how should we do it ? the example contains dummy colors :

    (* encode 1 second of video *)
  
    idx := 1;
  
    for i := 0 to 25 - 1 do
  
    begin
  
      av_init_packet(@pkt);
  
      pkt.data := nil;    // packet data will be allocated by the encoder
  
      pkt.size := 0;
  
  
  
      //fflush(stdout);
  
      (* prepare a dummy image *)
  
      (* Y *)
  
      for y := 0 to c.height - 1 do
  
        for x := 0 to c.width - 1 do
  
          PByte(@PAnsiChar(frame.data[0])[y * frame.linesize[0] + x])^ := x + y + i * 3;
  
  
  
      (* Cb and Cr *)
  
      for y := 0 to c.height div 2 - 1 do
  
        for x := 0 to c.width div 2 - 1 do
  
        begin
  
          PByte(@PAnsiChar(frame.data[1])[y * frame.linesize[1] + x])^ := 128 + y + i * 2;
  
          PByte(@PAnsiChar(frame.data[2])[y * frame.linesize[2] + x])^ := 64 + x + i * 5;
  
        end;
  
  
  
      frame.pts := i;
  
  
  
      (* encode the image *)
  
      ret := avcodec_encode_video2(c, @pkt, frame, @got_output);
  
      if ret < 0 then
  
      begin
  
        Writeln(ErrOutput, 'Error encoding frame');
  
        ExitCode := 1;
  
        Exit;
  
      end;
  
  
  
      if got_output <> 0 then
  
      begin
  
        Writeln(Format('Write frame %d (size=%d)', [idx, pkt.size]));
  
        FileWrite(f, pkt.data^, pkt.size);
  
        av_packet_unref(@pkt);
  
        Inc(idx);
  
      end;
  
    end;

  But we need to convert bitmaps to YCbCr..instead of filling pixels with dummy image. Here is a full source code :

  (*
  
   * Video encoding example
  
   *)
  
  procedure video_encode_example(const filename: string; codec_id: TAVCodecID);
  
  const
  
    endcode: array[0..3] of Byte = ( 0, 0, 1, $b7 );
  
  var
  
    codec: PAVCodec;
  
    c: PAVCodecContext;
  
    idx, i, ret, x, y, got_output: Integer;
  
    f: THandle;
  
    frame: PAVFrame;
  
    pkt: TAVPacket;
  
  begin
  
    Writeln(Format('Encode video file %s', [filename]));
  
  
  
    (* find the mpeg1 video encoder *)
  
    codec := avcodec_find_encoder(codec_id);
  
    if not Assigned(codec) then
  
    begin
  
      Writeln(ErrOutput, 'Codec not found');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    c := avcodec_alloc_context3(codec);
  
    if not Assigned(c) then
  
    begin
  
      Writeln(ErrOutput, 'Could not allocate video codec context');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    (* put sample parameters *)
  
    c.bit_rate := 400000;
  
    (* resolution must be a multiple of two *)
  
    c.width := 352;
  
    c.height := 288;
  
    (* frames per second *)
  
    c.time_base.num := 1;
  
    c.time_base.den := 25;
  
    (* emit one intra frame every ten frames
  
     * check frame pict_type before passing frame
  
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
  
     * then gop_size is ignored and the output of encoder
  
     * will always be I frame irrespective to gop_size
  
     *)
  
    c.gop_size := 10;
  
    c.max_b_frames := 1;
  
    c.pix_fmt := AV_PIX_FMT_YUV420P;
  
  
  
    if codec_id = AV_CODEC_ID_H264 then
  
      av_opt_set(c.priv_data, 'preset', 'slow', 0);
  
  
  
    (* open it *)
  
    if avcodec_open2(c, codec, nil) < 0 then
  
    begin
  
      Writeln(ErrOutput, 'Could not open codec');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    f := FileCreate(filename);
  
    if f = INVALID_HANDLE_VALUE then
  
    begin
  
      Writeln(ErrOutput, Format('Could not open %s', [filename]));
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    frame := av_frame_alloc();
  
    if not Assigned(frame) then
  
    begin
  
      Writeln(ErrOutput, 'Could not allocate video frame');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
    frame.format := Ord(c.pix_fmt);
  
    frame.width  := c.width;
  
    frame.height := c.height;
  
  
  
    (* the image can be allocated by any means and av_image_alloc() is
  
     * just the most convenient way if av_malloc() is to be used *)
  
    ret := av_image_alloc(@frame.data[0], @frame.linesize[0], c.width, c.height,
  
                         c.pix_fmt, 32);
  
    if ret < 0 then
  
    begin
  
      Writeln(ErrOutput, 'Could not allocate raw picture buffer');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    (* encode 1 second of video *)
  
    idx := 1;
  
    for i := 0 to 25 - 1 do
  
    begin
  
      av_init_packet(@pkt);
  
      pkt.data := nil;    // packet data will be allocated by the encoder
  
      pkt.size := 0;
  
  
  
      //fflush(stdout);
  
      (* prepare a dummy image *)
  
      (* Y *)
  
      for y := 0 to c.height - 1 do
  
        for x := 0 to c.width - 1 do
  
          PByte(@PAnsiChar(frame.data[0])[y * frame.linesize[0] + x])^ := x + y + i * 3;
  
  
  
      (* Cb and Cr *)
  
      for y := 0 to c.height div 2 - 1 do
  
        for x := 0 to c.width div 2 - 1 do
  
        begin
  
          PByte(@PAnsiChar(frame.data[1])[y * frame.linesize[1] + x])^ := 128 + y + i * 2;
  
          PByte(@PAnsiChar(frame.data[2])[y * frame.linesize[2] + x])^ := 64 + x + i * 5;
  
        end;
  
  
  
      frame.pts := i;
  
  
  
      (* encode the image *)
  
      ret := avcodec_encode_video2(c, @pkt, frame, @got_output);
  
      if ret < 0 then
  
      begin
  
        Writeln(ErrOutput, 'Error encoding frame');
  
        ExitCode := 1;
  
        Exit;
  
      end;
  
  
  
      if got_output <> 0 then
  
      begin
  
        Writeln(Format('Write frame %d (size=%d)', [idx, pkt.size]));
  
        FileWrite(f, pkt.data^, pkt.size);
  
        av_packet_unref(@pkt);
  
        Inc(idx);
  
      end;
  
    end;
  
  
  
    (* get the delayed frames *)
  
    repeat
  
      //fflush(stdout);
  
  
  
      ret := avcodec_encode_video2(c, @pkt, nil, @got_output);
  
      if ret < 0 then
  
      begin
  
        Writeln(ErrOutput, 'Error encoding frame');
  
        ExitCode := 1;
  
        Exit;
  
      end;
  
  
  
      if got_output <> 0 then
  
      begin
  
        Writeln(Format('Write frame %d (size=%d)', [idx, pkt.size]));
  
        FileWrite(f, pkt.data^, pkt.size);
  
        av_packet_unref(@pkt);
  
        Inc(idx);
  
      end;
  
    until got_output = 0;
  
  
  
    (* add sequence end code to have a real mpeg file *)
  
    FileWrite(f, endcode[0], SizeOf(endcode));
  
    FileClose(f);
  
  
  
    avcodec_close(c);
  
    av_free(c);
  
    av_freep(@frame.data[0]);
  
    av_frame_free(@frame);
  
    Writeln('');
  
  end;

  yes we know this formula, but what should we do with (* Cb and Cr *) loop that goes up to c.height div 2 - 1 and c.width div 2 - 1 ? all our experiments make correct image geometry but incorrect colors... Here is what we have :

  ( Y )
  
      for y := 0 to c.height - 1 do
  
      begin
  
        Line := image.ScanLine[y];
  
        for x := 0 to c.width - 1 do
  
        begin
  
          Yy := Round(Line[x].R*0.29900 + Line[x].G*0.58700 + Line[x].B*0.11400);
  
          PByte(@PAnsiChar(frame.data[0])[y * frame.linesize[0] + x])^ := Yy;
  
        end;
  
      end;
  
      ( Cb and Cr )
  
      for y := 0 to c.height div 2 - 1 do
  
      begin
  
        Pixels := image.ScanLine[y];
  
        for x := 0 to c.width div 2 - 1 do
  
        begin
  
          Cb := Round(Line[x].R  -0.16874 - Line[x].G  0.33126 + Line[x].B * 0.50000) + 128;
  
          Cr := Round(Line[x].R   0.50000 - Line[x].G  0.41869 - Line[x].B * 0.08131) + 64;
  
          PByte(@PAnsiChar(frame.data[1])[y * frame.linesize[1] + x])^ := Cr;
  
          PByte(@PAnsiChar(frame.data[2])[y * frame.linesize[2] + x])^ := Cb;
  
          //PByte(@PAnsiChar(frame.data[1])[y  frame.linesize[1] + x])^ := 128 + y + i  2;
  
          //PByte(@PAnsiChar(frame.data[2])[y  frame.linesize[2] + x])^ := 64 + x + i  5;
  
        end;
  
      end;

  How this should be fixed ?

• duration change after transcode ts

  25 décembre 2017, par Feilong Luo

  i have a problem about transcode with ffmpeg

  i want to cover m3u8 to mp4, so i transcode every ts file first, and then concat them to a mp4, but i found that the duration will be bigger than source file.

  source file is :
  http://oc7iy3eta.bkt.clouddn.com/src_20.ts

  after transcode, test file is :
  http://oc7iy3eta.bkt.clouddn.com/test_20.ts

  i use the command as bellow to change to 5fps, and 400k bitrate :

  sudo ffmpeg -analyzeduration 2147483647 -probesize 2147483647 -nostdin -y -v warning -i ./src_20.ts -threads 3 -movflags faststart -metadata:s:v rotate=0 -chunk_duration 520000 -video_track_timescale 25000 -pix_fmt yuv420p -copytb 1 -vcodec libx264 -b:v 400000 -minrate 400000 -maxrate 400000 -bufsize 500k -force_key_frames "expr:gte(t,n_forced*2)" -vsync 1 -r 5 -s 544*960 -acodec libfaac -async 1 ./test_20.ts

  i use ffprobe command to see video info :

  source file info :

  Duration : 00:00:01.26, start : 28.346989, bitrate : 921 kb/s
  Program 1
  Metadata :
  service_name : Service01
  service_provider : FFmpeg
  Stream #0:0[0x100] : Audio : aac ([15][0][0][0] / 0x000F), 44100 Hz, stereo, fltp, 23 kb/s
  Stream #0:1[0x101] : Video : h264 (High) ([27][0][0][0] / 0x001B), yuv420p, 544x960, 10.67 tbr, 90k tbn, 180k tbc

  test file :

  Input #0, mpegts, from ’test_20.ts’ :
  Duration : 00:00:01.62, start : 1.576778, bitrate : 447 kb/s
  Program 1
  Metadata :
  service_name : Service01
  service_provider : FFmpeg
  Stream #0:0[0x100] : Video : h264 (High) ([27][0][0][0] / 0x001B), yuv420p, 544x960, 5 fps, 5 tbr, 90k tbn, 10 tbc
  Stream #0:1[0x101] : Audio : aac ([15][0][0][0] / 0x000F), 44100 Hz, stereo, fltp, 5 kb/s

  =======================================================================

  question

  so , we can see that the duration of src file is 1.26s , but after transcode, the test file is 1.62s.

  why ? can anybody help