dxhead.c

xmms-1.2.10.tar.gz学习使用的就下吧

/*
 * Handle Xing vbr header
 */  
#include "config.h"
#include "dxhead.h"
#include <stdlib.h>
#include <stdio.h>
#include <float.h>
#include <math.h>
#include <string.h>
#include <glib.h>

#define GET_INT32BE(b) \
(i = (b[0] << 24) | (b[1] << 16) | b[2] << 8 | b[3], b += 4, i)

int mpg123_get_xing_header(xing_header_t * xing, unsigned char *buf)
{	
	int i, head_flags;
	int id, mode;
	
	memset(xing, 0, sizeof(xing_header_t));
	
	/* get selected MPEG header data */ 
	id = (buf[1] >> 3) & 1;
	mode = (buf[3] >> 6) & 3;
	buf += 4;
	
	/* Skip the sub band data */
	if (id)
	{
		/* mpeg1 */
		if (mode != 3)
			buf += 32;
		else
			buf += 17;
	}
	else
	{
		/* mpeg2 */
		if (mode != 3)
			buf += 17;
		else
			buf += 9;
	}
	
	if (strncmp(buf, "Xing", 4))
		return 0;
	buf += 4;
		
	head_flags = GET_INT32BE(buf);
	
	if (head_flags & FRAMES_FLAG)
		xing->frames = GET_INT32BE(buf);
	if (xing->frames < 1)
		return 0;
	if (head_flags & BYTES_FLAG)
		xing->bytes = GET_INT32BE(buf);
	
	if (head_flags & TOC_FLAG)
	{
		for (i = 0; i < 100; i++)
		{
			xing->toc[i] = buf[i];
			if (i > 0 && xing->toc[i] < xing->toc[i - 1])
				return 0;
		}
		if (xing->toc[99] == 0)
			return 0;
		buf += 100;
	}
	else
		for (i = 0; i < 100; i++)
			xing->toc[i] = (i * 256) / 100;
	
#ifdef XING_DEBUG
	for (i = 0; i < 100; i++)
	{
		if ((i % 10) == 0)
			fprintf(stderr, "\n");
		fprintf(stderr, " %3d", xing->toc[i]);
	}
#endif
	
	return 1;
}

int mpg123_seek_point(xing_header_t * xing, float percent)
{
	/* interpolate in TOC to get file seek point in bytes */ 
	int a, seekpoint;
	float fa, fb, fx;
		
	percent = CLAMP(percent, 0, 100);
	a = MIN(percent, 99);
	
	fa = xing->toc[a];
	
	if (a < 99)
		fb = xing->toc[a + 1];
	else
		fb = 256;
	
	fx = fa + (fb - fa) * (percent - a);
	seekpoint = (1.0f / 256.0f) * fx * xing->bytes;

	return seekpoint;
}