X264 Encoder API

Question

I'm studying the X264 API for encoding images.

So far I've built the X264 library and the following code snippet shows how far I am:

  int frame_size;
  x264_t* encoder;
  x264_picture_t pic_in, pic_out;
  x264_param_t x264Param;
  int fps = 20;
  int width = 1280;
  int height = 720;
  x264_nal_t* nals;
  int i_nals;

  x264_param_default_preset(&x264Param, "veryfast", "zerolatency");
  x264Param.i_threads = 1;
  x264Param.i_width = 1280;
  x264Param.i_height = 720;
  x264Param.i_fps_num = fps;
  x264Param.i_fps_den = 1;
  x264Param.i_keyint_max = fps;
  x264Param.b_intra_refresh = 1;
  x264Param.rc.i_rc_method = X264_RC_CRF;
  x264Param.rc.f_rf_constant = 25;
  x264Param.rc.f_rf_constant_max = 35;
  x264Param.b_repeat_headers = 1;
  x264Param.b_annexb = 1;
  x264_param_apply_profile(&x264Param, "baseline");

  encoder = x264_encoder_open(&x264Param);

  x264_picture_alloc(&pic_in, X264_CSP_BGR, width, height);

  /* How to fill in bitmap data? */

  frame_size = x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);
  if (frame_size >= 0)
  {
      printf("OK\n");
  }

So I'm trying to encode a 24bit BGR bitmap image. However, the x264 header file doesn't show any API function for writing the bitmap image to the encoder. How is this done?

EDIT

This code snippet seems to work. I would appreciate a review and some comments. Thanks.

  int frame_size;
  int accum_frame_size;
  x264_t* encoder;
  x264_picture_t pic_in, pic_out;
  x264_param_t x264Param;
  int fps = 20;
  int width = 1280;
  int height = 720;
  x264_nal_t* nals;
  int i_nals;
  int64_t frameCount = 0;
  int k;

  for (k = 0; k < (1280*3*720); k++)
  {
     bgr[k] = rand();
  }

  x264_param_default_preset(&x264Param, "veryfast", "zerolatency");
  x264Param.i_threads = 1;
  x264Param.i_width = 1280;
  x264Param.i_height = 720;
  x264Param.i_fps_num = fps;
  x264Param.i_fps_den = 1;
  x264Param.i_keyint_max = fps;
  x264Param.b_intra_refresh = 1;
  x264Param.rc.i_rc_method = X264_RC_CRF;
  x264Param.i_csp = X264_CSP_BGR;
  x264Param.rc.f_rf_constant = 25;
  x264Param.rc.f_rf_constant_max = 35;
  x264Param.b_repeat_headers = 1;
  x264Param.b_annexb = 1;
  x264_param_apply_profile(&x264Param, "baseline");

  encoder = x264_encoder_open(&x264Param);

  x264_picture_alloc(&pic_in, X264_CSP_BGR, width, height);

  /* Load 24-bit BGR bitmap */
  pic_in.img.i_csp = X264_CSP_BGR;
  pic_in.img.i_plane = 1;
  pic_in.img.i_stride[0] = 3 * 1280;
  pic_in.img.plane[0] = bgr;
  pic_in.i_pts = frameCount;
  pic_in.i_type = X264_TYPE_AUTO;
  pic_out.i_pts = frameCount;

  /* Returns a frame size of 912 for first frame in this case */
  frame_size = x264_encoder_encode(encoder, &nals, &i_nals, &pic_in, &pic_out);

  printf("Decoder returned frame size = %d \n", frame_size);
  printf("Decoder returned %d NAL units \n", i_nals);
  if (frame_size >= 0)
  {
     int i;
     int j;


     accum_frame_size = 0;
     for (i = 0; i < i_nals; i++)
     {
        printf("******************* NAL %d (%d bytes) *******************\n", i, nals[i].i_payload);
        for (j = 0; j < nals[i].i_payload; j++)
        {
           if (j == 0) printf("First 10 bytes: ");
           if (j < 10) printf("%02X |", nals[i].p_payload[j]);
           accum_frame_size++;
        }
        printf("\n");

     }
  }

  printf("Verified frame size = %d \n", accum_frame_size);

EDIT #2 The encoder outputs this:

     x264 [error]: baseline profile doesn't support 4:4:4
     x264 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
     x264 [info]: profile High 4:4:4 Predictive, level 3.1, 4:4:4 8-bit
     Decoder returned frame size = 1467194
     Decoder returned 4 NAL units
     ******************* NAL 0 (31 bytes) *******************
     First 10 bytes: 00 |00 |00 |01 |67 |F4 |00 |1F |91 |89 |
     ******************* NAL 1 (8 bytes) *******************
     First 10 bytes: 00 |00 |00 |01 |68 |EF |1F |2C |
     ******************* NAL 2 (595 bytes) *******************
     First 10 bytes: 00 |00 |01 |06 |05 |FF |FF |4C |DC |45 |
     ******************* NAL 3 (1466560 bytes) *******************
     First 10 bytes: 00 |00 |01 |65 |88 |82 |0A |FF |F5 |B0 |
     Verified frame size = 1467194

Isn't each NAL unit supposed to start with 0x00 0x00 0x00 0x01 ?

szatmary : I appreciate your valuable feedback. So you're saying that each NAL unit does not necessarily start with 0,0,0,1. However, I'm a bit unclear on your answer. Are you implying that with a certain configuration the NAL units will start with 0,0,0,1 ? If so, which configuration is that? I need to make sure that each NAL unit I transmit out on the network to a remote receiver starts with 0,0,0,1. Prior to exploring the x264 library I was using the x264 exe and piped BMP data in and encoded data out from the x264 process. I then parsed the encoder output and looked for NAL units by looking for 0,0,0,1. How do I accomplish the same with the x264 library?

Regarding libswscale:

I downloaded the ffmpeg source and ran configure and make in MINGW. After the process had completed I couldn't find anything but a number of .exe files. How do I build actual static libraries (.lib) which I can use in a Visual Studio project?

Answer 1

x264 can not encode BGR. You must convert the image to YUV 4:2:0p. I recommend using libswscale from the ffmpeg project to perform this operation.

EDIT #2

No, a startcode is at least two 0x00 bytes followed by a 0x01. But it can have any number (But is usually two or three null bytes) The 4 byte version is used for detecting byte alighnemnt in serial transmissions and generally precedes SPS and PPS NALUs.