2007.11.14 15:45
     

참고. DPG 파일 포맷

원문 :  http://kkamagui.springnote.com/pages/492957

 

들어가기 전에...

 

0.시작하면서...

 문쉘(MoonShell)의 동영상 포맷인 DPG에 대해서 알아보자.

 

1.파일 포맷(File Format)

 아래는 Wikipedia에 등록된 내용이다.

File Format

[edit] General Outline

The DPG file specification is simple. All DPG files contain a 36 byte header, followed by audio, and then a standard mpeg-1 video stream. The audio format can differ; older DPG files used a special WAV format audio, but newer versions of moonshell have phased that out in favor of MP2 audio.

[edit] File Structure

The file begins with a 36 byte header (Note: all of the numbers below are hexadecimal.):

  • 44 50 47 30 (this stands for DPG0 in ASCII)
  • Four bytes for the number of frames in the video
  • Two bytes for the frames per second that the video runs
  • 00 00
  • Four bytes for the audio sample rate
  • 00 00 00 00 (this was the number of audio channels, now deprecated in favor of MP2 audio)
  • 24 00 00 00 (this is the start of the audio file, i.e. right after the header)
  • Four bytes for the length, in bytes, of the audio
  • Four bytes for the above length + 36 bytes (i.e. the start of the video file)
  • Four bytes for the length, in bytes, of the video

(A C program and source is included in the BatchDPG source code to simplify the header generation)

After a header has been made, concatenate everything together:

  • Linux & Mac (OS X Terminal): cat header.head audio.mp2 video.raw.mpg > ndsmpeg.dpg
  • Windows: copy /b header.head + audio.mp2 + video.raw.mpg ndsmpeg.dpg

[edit] Audio Encoding

The audio is encoded in standard MP2 format. For example, using ffmpeg to encode in.avi into out.mp2 at a 22050 sample rate and a bitrate of 64 kb/s:

ffmpeg -i in.avi -vn -ab 64k -ar 22050 out.mp2

[edit] Video Encoding

MoonShell can be very particular about the types of MPEG video it will decode correctly. Videos made with ffmpeg do not work very well; MEncoder seems to be a better option. The FPS and bitrate rely on personal preference, but the DS does not have much processing power - lower bitrates and framerates seem to work better. Finally, since the DS screen is so small, rescaling to 256 by 192 is the most space-efficient.

Here is an example command using MEncoder (this should be on one line):

mencoder in.avi -o out.mpg -nosound -ovc lavc -lavcopts vcodec=mpeg1video:vrc_buf_size=327:vrc_maxrate=512:vbitrate=256:vstrict=-1 -ofps 18 -vf scale=256:192

This produces an AVI with a working MPEG video stream, but it should be extracted into a raw format with ffmpeg, however, this is not required:

ffmpeg -i out.mpg -an -vcodec copy -f mpeg1video out.raw.mpg

Or, in more recent versions of mencoder you can just add the following option:

-of rawvideo

This makes MEncoder output raw video with no need to extract it later with ffmpeg.

 

 

2.DPG 파일 생성 소스

  1. #include "stdio.h"
    #include "stdlib.h"
  2. void putint(unsigned int i, FILE* outfile) {
       fputc(i & 0xff, outfile);
       i >>= 8;
       fputc(i & 0xff, outfile);
       i >>= 8;
       fputc(i & 0xff, outfile);
       i >>= 8;
       fputc(i & 0xff, outfile);
    }
  3. int main(int argc, char* argv[]) {
       int frames;
       int fps;
       int samplerate;
       int audiosize;
       int videosize;
      
       //char* filename = "header",0;
       FILE* outfile;
      
       if (argc != 7) {
          printf("usage: headermaker <frames> <fps> <samplerate> <audiosize> <videosize> <filename>\n");
          return -1;
       }
      
       // read our parameters
       frames  = atoi(argv[1]);
       fps   = atoi(argv[2]);
       samplerate = atoi(argv[3]);
       audiosize = atoi(argv[4]);
       videosize = atoi(argv[5]);
      
       outfile = fopen(argv[6], "wb");
      
       // magic number:
       fputc(0x44, outfile);
       fputc(0x50, outfile);
       fputc(0x47, outfile);
       fputc(0x30, outfile);
      
       // frames
       putint(frames, outfile);
      
       // fps
       fputc(0x00, outfile);
       fputc(fps%256, outfile);
      
       fputc(0x00, outfile);
       fputc(0x00, outfile);
      
       // samplerate
       putint(samplerate, outfile);
      
       // channels
       putint(0, outfile);
      
       // begin and size audio
       putint(36, outfile);
       putint(audiosize, outfile);
      
       // begin and size video
       putint(36+audiosize, outfile);
       putint(videosize, outfile);
      
       fclose(outfile);
      
       return 0;
    }

 

3.마치면서...

 아주 간단한 파일 포맷이다. 시간나면 인코딩 라이브러리를 이용해서 직접 생성해봐야겠다.

 

 

 

이 글은 스프링노트에서 작성되었습니다.

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