我有一些mpeg ts位域,例如传输流包:
struct ts_package_header_s {
unsigned int continuity_counter :4;
unsigned int adaptation_field_control :2;
unsigned int transport_scrambling_control :2;
unsigned int PID :13;
unsigned int transport_priority :1;
unsigned int payload_unit_start_indicator :1;
unsigned int transport_error_indicator :1;
unsigned int sync_byte :8;
};
struct ts_package_s {
struct ts_package_header_s ts_header;
unsigned char ts_body[TS_BODY];
};
union ts_package_u {
struct ts_package_s ts_package;
unsigned char bytes[TS_PACKAGE];
};
在我的源代码中,我初始化头文件结构:
pat_package_header.sync_byte = 0x47;
pat_package_header.transport_error_indicator = 0;
pat_package_header.payload_unit_start_indicator = 1;
pat_package_header.transport_priority = 0;
pat_package_header.PID = PAT_PID;
pat_package_header.transport_scrambling_control = 0;
pat_package_header.adaptation_field_control = 1;
pat_package_header.continuity_counter = 0;
而不是我制作ts_packag联盟
union ts_package_u package;
package.ts_package.ts_header = pat_package_header;
比我填充ts_body数组。 当我把这个包写入文件时。我倒退了数组:
10 00 40 47 XX XX XX.. instead of 47 40 10 00 XX XX XX..
我试图将我的结构转换为char *而不是使用union,但结果相同。
哪里有错?感谢。
答案 0 :(得分:3)
将try和serialise这样的结构直接用于磁盘是危险的,其中必须在不同的体系结构中知道格式,或者使用不同的编译器。
编译器存储位域的方式不同,架构的基础字节也会改变数据的存储方式
例如,可能是编译器选择在字节,字或其他边界上对齐位域。这是编译器的决定。它也可以选择以任何顺序保存位,这通常取决于机器的字节顺序。
为了安全地将此标头写入磁盘,您需要自己序列化数据。根据{{3}}
,标题为32位和Big Endian例如:
#include <stdio.h>
#define TS_BODY 1024
#define PAT_PID 0x40
struct ts_package_header_s {
unsigned int continuity_counter :4;
unsigned int adaptation_field_control :2;
unsigned int transport_scrambling_control :2;
unsigned int PID :13;
unsigned int transport_priority :1;
unsigned int payload_unit_start_indicator :1;
unsigned int transport_error_indicator :1;
unsigned int sync_byte :8;
};
struct ts_package_s {
struct ts_package_header_s ts_header;
unsigned char ts_body[TS_BODY];
};
static void write_ts( struct ts_package_s pat_package )
{
FILE* f = fopen( "test.ts", "wb+" );
unsigned int header = 0;
if( f == NULL )
return;
header = pat_package.ts_header.sync_byte << 24;
header |= ( pat_package.ts_header.transport_error_indicator << 23 );
header |= ( pat_package.ts_header.payload_unit_start_indicator << 22 );
header |= ( pat_package.ts_header.transport_priority << 21 );
header |= ( pat_package.ts_header.PID << 8 );
header |= ( pat_package.ts_header.transport_scrambling_control << 6 );
header |= ( pat_package.ts_header.adaptation_field_control << 4 );
header |= ( pat_package.ts_header.continuity_counter );
/* Write the 32-bit header as big-endian */
unsigned char byte = header >> 24;
fwrite( &byte, 1, 1, f );
byte = ( header >> 16 ) & 0xFF;
fwrite( &byte, 1, 1, f );
byte = ( header >> 8 ) & 0xFF;
fwrite( &byte, 1, 1, f );
byte = header & 0xFF;
fwrite( &byte, 1, 1, f );
fclose( f );
}
int main( int argc, char* argv[] )
{
struct ts_package_s pat_package;
pat_package.ts_header.sync_byte = 0x47;
pat_package.ts_header.transport_error_indicator = 0;
pat_package.ts_header.payload_unit_start_indicator = 1;
pat_package.ts_header.transport_priority = 0;
pat_package.ts_header.PID = PAT_PID;
pat_package.ts_header.transport_scrambling_control = 0;
pat_package.ts_header.adaptation_field_control = 1;
pat_package.ts_header.continuity_counter = 0;
write_ts( pat_package );
return 0;
}
使用以下标题写入文件:
0x47 0x40 0x01 0x10
根据您使用的值,似乎是正确的。