- x264_nal_t结构体
typedef struct x264_nal_t
{
int i_ref_idc; /* nal_priority_e */
int i_type; /* nal_unit_type_e */
int b_long_startcode;
int i_first_mb; /* If this NAL is a slice, the index of the first MB in the slice. */
int i_last_mb; /* If this NAL is a slice, the index of the last MB in the slice. */
/* Size of payload (including any padding) in bytes. */
int i_payload;
/* If param->b_annexb is set, Annex-B bytestream with startcode.
* Otherwise, startcode is replaced with a 4-byte size.
* This size is the size used in mp4/similar muxing; it is equal to i_payload-4 */
uint8_t *p_payload;
/* Size of padding in bytes. */
int i_padding;
} x264_nal_t;
i_ref_idc：nal_t的优先级。其包含的几个优先级的定义如下：
enum nal_priority_e
{
NAL_PRIORITY_DISPOSABLE = 0, // 00
NAL_PRIORITY_LOW = 1, // 01
NAL_PRIORITY_HIGH = 2, // 10
NAL_PRIORITY_HIGHEST = 3, // 11
};
i_type：nal_t的类型。包括SPS,PPS,SS等信息，其类型信息的定义如下：
enum nal_unit_type_e
{
NAL_UNKNOWN = 0, // 00000
NAL_SLICE = 1, // 00001
NAL_SLICE_DPA = 2, // 00010
NAL_SLICE_DPB = 3, // 00011
NAL_SLICE_DPC = 4, // 00100
NAL_SLICE_IDR = 5, /* ref_idc != 0 */ // 00101
NAL_SEI = 6, /* ref_idc == 0 */ // 00110
NAL_SPS = 7, // 00111
NAL_PPS = 8, // 01000
NAL_AUD = 9, // 01001
NAL_FILLER = 12, // 01100
/* ref_idc == 0 for 6,9,10,11,12 */
};
b_long_startcode：最长的开始编码，有可能是3或者4，这是由于nal的首部是以000001或者00000001开始的，包含3字节或者两个字节。
i_payload,p_payload,i_padding：待观察其使用。
