MPEG-2 文件结构解析

一个完整的MPEG-2文件就是一个PS流文件。spa

MPEG-2文件的构造格式以下图：.net

本身找个mpg文件打开，能够看到文件以0x0000 01B9结束（有些文件不标准没有），即MPEG_Program_end_code，以前有不少个0x0000 00BA字段，即为program pack的开始标志，program pack包的构造以下：rest

能够看出program pack由3部分组成：pack_header+system_header+PES_packets,其中system_header当且仅当pack是第一个数据包时才存在。system_header和PES_packets构造以下：code

对照文件内容，各字段顺序、长度以下：orm

pack_header： 起始地址：0x0000 0000（这个地址有可能由于文件不同而不同）视频

标志：0x00 0x00 0x01 0xBA（4B)

struct PackHeader
{
	unsigned paddingByte				: 2;
	unsigned program_clock_reference_base		: 3;
	unsigned marker1				: 1;
	unsigned SCR_base1				: 15;
	unsigned marker2				: 1;
	unsigned SCR_base2				: 15;
	unsigned marker3				: 1;
	unsigned SCR_externsion				: 9;
	unsigned marker4				: 1;

	unsigned mutiplex_rate				: 22;
	unsigned marker5				: 1;
	unsigned marker6				: 1;

	unsigned reserved				: 5;
	unsigned stuffing_length			: 3;
};

system_header: 起始地址：0x0000 000eip

标志(4B)：0x00 0x00 0x01 0xBB （4B）

struct SystemHeader//112bit
{
	unsigned head_length				: 16;
	unsigned marker1				: 1;
	unsigned rate_bound				: 22;
	unsigned marker2				: 1;
	unsigned audio_bound				: 6;
	unsigned fixed_flag				: 1;
	unsigned CSPS_flag				: 1;

	unsigned system_audio_local_flag		: 1;
	unsigned system_video_local_flag		: 1;
	unsigned marker3				: 1;
	unsigned video_bound				: 5;

	unsigned packet_rate_restriction_flag	<span style="white-space:pre">	</span>: 1;
	unsigned reserved				: 7;

	unsigned stream_id1				: 8;

	unsigned paddingByte1				: 2;
	unsigned P_STD_buffer_bound_scale1		: 1;
	unsigned P_STD_buffer_size_bound1		: 13;

	unsigned stream_id2				: 8;

	unsigned paddingByte2				: 2;
	unsigned P_STD_buffer_bound_scale2		: 1;
	unsigned P_STD_buffer_size_bound2		: 13;
};

PES packet：起始地址：0x0000 0020

标志位(3B)：0x 00 00 01

stream_id(1B)：0xBE(BE为Padding stream)

PES_packet_length(2B)：0x07 DA，跳过该长度的填充字节，恰好为下一个pack的起始标志：0x000001BA

从0x0800地址开始为第二个pack包，该包的构造格式为pack_header+PES，分析以下：

pack_header： 起始地址：0x0000 0800

(此包上面已经讲到，这里再也不赘述)

PES packet：起始地址：0x0000 080e

标志位(3B)：0x 00 00 01

stream_id(1B)：0xE0(视频)

struct PESPacket
{
	unsigned PES_packet_length			: 16;

	unsigned paddingByte1				: 2;
	unsigned scrambling_control			: 2;
	unsigned priority				: 1;
	unsigned alignment				: 1;
	unsigned copyright				: 1;
	unsigned original				: 1;

	unsigned PTS_DTS_flag				: 2;
	unsigned ESCR_flag				: 1;
	unsigned ES_rate_flag				: 1;
	unsigned DSM_trick_mode_flag		: 1;
	unsigned additional_copy_info_flag	: 1;
	unsigned CRC_flag				: 1;
	unsigned extension_flag				: 1;

	unsigned PES_header_data_length		: 8;

	unsigned paddingByte2				: 4;
	unsigned PTS_32_30				: 3;//pts 的第32-30位
	unsigned marker1				: 1;

	unsigned PTS_29_15				: 15;//pts的第29-15位
	unsigned marker2				: 1;

	unsigned PTS_14_0				: 15;//pts的第14-0位（共33位）
	unsigned marker3				: 1;

	unsigned paddingByte3				: 4;
	unsigned DTS_32_30				: 3;
	unsigned marker4				: 1;

	unsigned DTS_29_15				: 15;
	unsigned marker5				: 1;

	unsigned DTS_14_0				: 15;
	unsigned marker6				: 1;
};

Video Sequence，其结构定义以下：

图中sequence_header，sequence entension等子内容定义以下：

对各字段顺序、长度分析以下：

sequence header：起始地址：0x0000 0821

标志位(4B)：0x00 0x00 0x01 0xB3

struct SequenceHeader
{
	unsigned horizontal_size		: 12;
	unsigned vertical_size			: 12;

	unsigned aspect_ratio_info		: 4;
	unsigned frame_rate			: 4;

	unsigned bit_rate			: 18;
	unsigned marker				: 1;
	unsigned VBV_buffer_size		: 10;
	unsigned constrained			: 1;
	unsigned load_intra_Q_matrix	: 1;
	unsigned paddingBit			: 1;
};

  sequence extension：起始地址：0x0000 082d；若是有这一项说明是MPEG-2文件，不然为MPEG-1文件

标志位(4B)：0x0000 01B5

struct SequenceExtension
{
	unsigned start_code_identifer		: 4;
	unsigned profile_level_escape		: 1;
	unsigned profile_level			: 7;
	unsigned progressive			: 1;
	unsigned chroma				: 2;
	unsigned horiz_extension		: 2;
	unsigned vertical_extension		: 2;
};

接下来的数据是0x0000 01B8，说明该序列中没有extension&user data[i]（extension data的开始符为0x0000 01B5，user data的开始符为0x0000 01B2），接下来的内容为Group of pictures header。

Group_of_pictures_header：起始地址：0x0000 0837

标志位(4B)：0x0000 01B8

struct GroupOfPicturesHeader
{
	unsigned time_code		: 25;
	unsigned closed_gop		: 1;
	unsigned broken_link	: 1;
};

extension & user data[1]：无

picture header: 起始地址：0x0000 083F

标志位(4B)：0x0000 0100

struct PictureHeader
{
	unsigned temporal_reference		: 10;
	unsigned picture_coding_type	: 3;
	unsigned vbv_delay			: 16;
	unsigned extra_bit_piture		: 1;
};

picture coding extension：起始地址：0x0000 0847

extension_start_code(4B)：0x0000 01B5

struct PictureCodingExtension
{
	unsigned extension_start_code_identifier		: 4;
	unsigned f_code_0_0					: 4;

	unsigned f_code_0_1					: 4;
	unsigned f_code_1_0					: 4;

	unsigned f_code_1_1					: 4;
	unsigned intra_dc_presison				: 2;
	unsigned picture_structure				: 2;

	unsigned top_field_first				: 1;
	unsigned frame_pred_frame_dct				: 1;
	unsigned concealment_motion_vectors			: 1;
	unsigned q_scale_type					: 1;
	unsigned intra_vlc_format				: 1;
	unsigned alternate_scan					: 1;
	unsigned repeat_first_field				: 1;
	unsigned chroma_420_type				: 1;

	unsigned progressive_frame				: 2;
	unsigned composite_display_flag				: 2;
};

extension & user data[2]：无

picture data: 起始地址：0x0000 0850（暂时未分析，之后补上）

MPEG-2 文件结构解析

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