/* qcifextr.c	extract certain frames from a QCIF sequence

author:		Leiming Qian <lqian@uiuc.edu>	*/

#define	ROW			144
#define COL			176

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>

int main(int argc, char* argv[])
{
	FILE *qcif_file_ptr;						/* qcif input file pointer */
	FILE *out_file_ptr;							/* Y, U, V file pointers */
	int start_n, stop_n;						/* start and stop frame index */
	struct stat file_status;				/* file status */
	char *frame_buffer;							/* extracted qcif frame sequences */
	long buffer_size;
	
	
	/* parsing the command line */
	if (argc!=5) {
		fprintf(stderr, "Usage: qcifextr qcif_file start_# stop_# out_file\n");
		exit(1);
	}
	else {
		/* open input qcif file */
		if (!(qcif_file_ptr=fopen(argv[1], "rb"))) {
			fprintf(stderr, "Can't open input qcif file!\n");
			exit(1);
		}
		/* read start and stop frame index, check validity */
		if ( (start_n=atoi(argv[2]))<0 || (stop_n=atoi(argv[3]))<0 ) {
      fprintf(stderr, "Invalid start and stop frame indexes!\n");
      exit(1);
    }
    if (start_n>stop_n) {
    	fprintf(stderr, "Start frame behind stop frame!\n");
    	exit(1);
    }
    /* read in qcif file size, see if enough frames exist */
    if (stat(argv[1], &file_status)) {
      fprintf(stderr, "Error occured in determining file size!\n");
      exit(2);
    }
    else {
      if ((buffer_size=file_status.st_size/ROW/COL/1.5)<stop_n) {
      	fprintf(stderr, "Not enough number of frames!\n");
      	exit(1);
      }
      printf("This qcif sequence contains %d frames\n", buffer_size);
    }
  }
  
  /* allocating memory */
  if ( !(frame_buffer=(char *)
  		malloc(buffer_size=ROW*COL*1.5*(stop_n-start_n+1)*sizeof(char))) ) {
    fprintf(stderr, "Can't allocate memory!\n\n");
    exit(1);
  }

	/* move the file location pointer to its correct place */
	if (fseek(qcif_file_ptr, COL*ROW*1.5*(start_n-1), SEEK_SET)) {
		fprintf(stderr, "File relocation operation failed!\n");
		exit(1);
	}
	
	/* read in the frame sequences */
	fread(frame_buffer, sizeof(char), buffer_size, qcif_file_ptr);
	if ( !(out_file_ptr=fopen(argv[4], "wb"))	) {
		fprintf(stderr, "Can't output file!\n");
		exit(1);
	}
	fwrite(frame_buffer, sizeof(char), buffer_size, out_file_ptr);
	
	/* free the memory and close the file */
	free(frame_buffer);
	fclose(qcif_file_ptr);
	fclose(out_file_ptr);
	
}