MP42Utilities.m

/*
 *  MP42Utilities.c
 *  Subler
 *
 *  Created by Damiano Galassi on 30/01/09.
 *  Copyright 2009 Damiano Galassi. All rights reserved.
 *
 */

#import "MP42Utilities.h"
#import <string.h>
#include "lang.h"

#define MP4ESDescrTag                   0x03
#define MP4DecConfigDescrTag            0x04
#define MP4DecSpecificDescrTag          0x05

// from perian
// based off of mov_mp4_read_descr_len from mov.c in ffmpeg's libavformat
static int readDescrLen(UInt8 **buffer)
{
	int len = 0;
	int count = 4;
	while (count--) {
		int c = *(*buffer)++;
		len = (len << 7) | (c & 0x7f);
		if (!(c & 0x80))
			break;
	}
	return len;
}

// based off of mov_mp4_read_descr from mov.c in ffmpeg's libavformat
static int readDescr(UInt8 **buffer, int *tag)
{
	*tag = *(*buffer)++;
	return readDescrLen(buffer);
}

// based off of mov_read_esds from mov.c in ffmpeg's libavformat
ComponentResult ReadESDSDescExt(void* descExt, UInt8 **buffer, int *size, int versionFlags)
{
	UInt8 *esds = (UInt8 *) descExt;
	int tag, len;
	*size = 0;

    if (versionFlags)
        esds += 4;		// version + flags
	readDescr(&esds, &tag);
	esds += 2;		// ID
	if (tag == MP4ESDescrTag)
		esds++;		// priority

	readDescr(&esds, &tag);
	if (tag == MP4DecConfigDescrTag) {
		esds++;		// object type id
		esds++;		// stream type
		esds += 3;	// buffer size db
		esds += 4;	// max bitrate
		esds += 4;	// average bitrate

		len = readDescr(&esds, &tag);
		if (tag == MP4DecSpecificDescrTag) {
			*buffer = calloc(1, len + 8);
			if (*buffer) {
				memcpy(*buffer, esds, len);
				*size = len;
			}
		}
	}

	return noErr;
}