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• Encoding with ffmpeg : video quality drops

  21 mai 2014, par Adi Ulici

  I’m trying to encode a set of pictures into a video with ffmpeg. I’m new to this stuff, but I managed to get it work. I have only one problem : the first second or two of video look good but as the time goes the video quality keeps dropping and dropping. At the end (it’s a video of about 16 seconds) the quality is really bad and I can’t understand why.

  I’m using AV_CODEC_ID_MPEG1VIDEO as video codec (frankly, it’s the only one I could make work) and here is a sample of my code :

  c = avcodec_alloc_context3(codec);
  
  if (!c) {
  
      fprintf(stderr, "Could not allocate video codec context\n");
  
      exit(1);
  
  }
  
  
  
  c->bit_rate = 400000;
  
  c->width = width;
  
  c->height = height;
  
  struct AVRational time_base = {1, 25};
  
  c->time_base = time_base;
  
  c->gop_size = 10;
  
  c->max_b_frames = 1;
  
  c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
  if (codec_id == AV_CODEC_ID_H264)
  
      av_opt_set(c->priv_data, "preset", "slow", 0);
  
  
  
  // Open the codec
  
  if (avcodec_open2(c, codec, NULL) < 0) {
  
      fprintf(stderr, "Could not open codec\n");
  
      exit(1);
  
  }
  
  
  
  fopen_s(&f, filename, "wb");
  
  if (!f) {
  
      fprintf(stderr, "Could not open %s\n", filename);
  
      exit(1);
  
  }
  
  
  
  frame = av_frame_alloc();
  
  if (!frame) {
  
      fprintf(stderr, "Could not allocate video frame\n");
  
      exit(1);
  
  }
  
  frame->format = c->pix_fmt;
  
  frame->width  = c->width;
  
  frame->height = c->height;
  
  
  
  ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height,
  
                       c->pix_fmt, 32);
  
  if (ret < 0) {
  
      fprintf(stderr, "Could not allocate raw picture buffer\n");
  
      exit(1);
  
  }
  
  
  
  struct SwsContext *frameConvertContext = sws_getContext(width, height,
  
        PIX_FMT_RGB24,
  
        c->width, c->height,
  
        c->pix_fmt,
  
        SWS_LANCZOS | SWS_ACCURATE_RND, NULL, NULL, NULL);
  
  
  
  for (i = 0; i < framesNr; i++) {
  
      // Read an image
  
      std::stringstream filename;
  
      filename << "input/image-" << (i+1) << ".jpg";
  
      Image* img;
  
      img = Image::fromJpeg((char*) filename.str().c_str());
  
      int srcSliceY[1] = { img->getWidth() * 3 };
  
      const uint8_t* imgbuf[1] = { (uint8_t*) img->getData(sizeof(uint8_t)) };
  
  
  
      av_init_packet(&pkt);
  
      pkt.data = NULL;
  
      pkt.size = 0;
  
  
  
      fflush(stdout);
  
      frameConvertContext = sws_getCachedContext(frameConvertContext, width, height,
  
        PIX_FMT_RGB24,
  
        c->width, c->height,
  
        c->pix_fmt,
  
        SWS_LANCZOS | SWS_ACCURATE_RND, NULL, NULL, NULL);
  
  
  
      sws_scale(frameConvertContext, imgbuf, srcSliceY, 0, img->getHeight(), frame->data, frame->linesize);
  
  
  
      frame->pts = i;
  
  
  
      /* encode the image */
  
      ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
  
      if (ret < 0) {
  
          fprintf(stderr, "Error encoding frame\n");
  
          exit(1);
  
      }
  
  
  
      if (got_output) {
  
          printf(".");
  
          fwrite(pkt.data, 1, pkt.size, f);
  
          av_free_packet(&pkt);
  
      }
  
  
  
      // Free the memory
  
      delete img;
  
  }

  Any tips ? Thanks a lot !

• Ffmpeg video encoding and decoding

  17 décembre 2014, par iJose

  I am a newbie to FFMPEG.
  I am trying to encode a video that is captured from the camera.
  I am using the following code to encode the video. i am capturing the frames using
  AvcaptureSession, i have also tried other library files
  Kickflip and iFrameExtractor from github.com but ended up with no solution.

  Please Help me Thanking you in advance

  static void video_encode_example(const char *filename, int codec_id)
  
  {
  
      AVCodec *codec;
  
      AVCodecContext *c= NULL;
  
      int i, ret, x, y, got_output;
  
      FILE *f;
  
      AVFrame *frame;
  
      AVPacket pkt;
  
      uint8_t endcode[] = { 0, 0, 1, 0xb7 };
  
  
  
      printf("Encode video file %s\n", filename);
  
  
  
      /* find the mpeg1 video encoder */
  
      codec = avcodec_find_encoder(codec_id);
  
      if (!codec) {
  
          fprintf(stderr, "Codec not found\n");
  
          exit(1);
  
      }
  
  
  
      c = avcodec_alloc_context3(codec);
  
      if (!c) {
  
          fprintf(stderr, "Could not allocate video codec context\n");
  
          exit(1);
  
      }
  
  
  
      /* 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= (AVRational){1,25};
  
      c->gop_size = 10; /* emit one intra frame every ten frames */
  
      c->max_b_frames=1;
  
      c->pix_fmt = AV_PIX_FMT_YUV420P;
  
  
  
      if(codec_id == AV_CODEC_ID_H264)
  
          av_opt_set(c->priv_data, "preset", "slow", 0);
  
  
  
      /* open it */
  
      if (avcodec_open2(c, codec, NULL) < 0) {
  
          fprintf(stderr, "Could not open codec\n");
  
          exit(1);
  
      }
  
  
  
      f = fopen(filename, "wb");
  
      if (!f) {
  
          fprintf(stderr, "Could not open %s\n", filename);
  
          exit(1);
  
      }
  
  
  
      frame = avcodec_alloc_frame();
  
      if (!frame) {
  
          fprintf(stderr, "Could not allocate video frame\n");
  
          exit(1);
  
      }
  
      frame->format = 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, frame->linesize, c->width, c->height,
  
                           c->pix_fmt, 32);
  
      if (ret < 0) {
  
          fprintf(stderr, "Could not allocate raw picture buffer\n");
  
          exit(1);
  
      }
  
  
  
      /* encode 1 second of video */
  
      for(i=0;i<25;i++) {
  
          av_init_packet(&pkt);
  
          pkt.data = NULL;    // packet data will be allocated by the encoder
  
          pkt.size = 0;
  
  
  
          fflush(stdout);
  
          /* prepare a dummy image */
  
          /* Y */
  
          for(y=0;yheight;y++) {
  
              for(x=0;xwidth;x++) {
  
                  frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
  
              }
  
          }
  
  
  
          /* Cb and Cr */
  
          for(y=0;yheight/2;y++) {
  
              for(x=0;xwidth/2;x++) {
  
                  frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
  
                  frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
  
              }
  
          }
  
  
  
          frame->pts = i;
  
  
  
          /* encode the image */
  
          ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
  
          if (ret < 0) {
  
              fprintf(stderr, "Error encoding frame\n");
  
              exit(1);
  
          }
  
  
  
          if (got_output) {
  
              printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
              fwrite(pkt.data, 1, pkt.size, f);
  
              av_free_packet(&pkt);
  
          }
  
      }
  
  
  
      /* get the delayed frames */
  
      for (got_output = 1; got_output; i++) {
  
          fflush(stdout);
  
  
  
          ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
  
          if (ret < 0) {
  
              fprintf(stderr, "Error encoding frame\n");
  
              exit(1);
  
          }
  
  
  
          if (got_output) {
  
              printf("Write frame %3d (size=%5d)\n", i, pkt.size);
  
              fwrite(pkt.data, 1, pkt.size, f);
  
              av_free_packet(&pkt);
  
          }
  
      }
  
  
  
      /* add sequence end code to have a real mpeg file */
  
      fwrite(endcode, 1, sizeof(endcode), f);
  
      fclose(f);
  
  
  
      avcodec_close(c);
  
      av_free(c);
  
      av_freep(&frame->data[0]);
  
      avcodec_free_frame(&frame);
  
      printf("\n");
  
  }

• How to encode with ffmpeg PCM to AAC with different sample formats ?

  1er août 2014, par user2212461

  I’m using the following code to encode PCM to AAC using libav. It works with sample_fmt = AV_SAMPLE_FMT_S16 ; and a newer release of liabv. In older versions, only sample_fmt = AV_SAMPLE_FMT_FLT is allowed, but then the decoder always returns 0 (nothing decoded). What in the code do I need to adapt in order to make it work with sample_fmt = AV_SAMPLE_FMT_S16 ? Is sample_fmt the input or output format ?

   avcodec_register_all();
  
   codec = avcodec_find_encoder(CODEC_ID_AAC);
  
   c = avcodec_alloc_context3(codec);
  
  
  
   c->bit_rate   = 64000;
  
   c->sample_rate= 44100;
  
   c->channels   = 1;
  
   c->frame_size = 86000;
  
   c->sample_fmt = AV_SAMPLE_FMT_FLT;//---> this works with AV_SAMPLE_FMT_S16
  
  
  
  buf = (uint8_t *)malloc(bufSize);
  
  audioData = (uint8_t *)malloc(size);
  
  
  
  //fill audioData
  
  
  
  int packetSize = avcodec_encode_audio(c, buf, bufSize, 
  
           (short *)audioData);//------>returns 0 when using AV_SAMPLE_FMT_FLT