我需要从原始H.264数据中解析图像大小。以下测试代码适用于我测试的情况，但现在如果在“Z0IAIOKQCgDLYC3AQEBpB4kRUA ==”上失败。结果应该是1280x800，但它给我640x1616：
public static void main(String[] args) {
decode(StringUtils.fromBase64("Z0IAKeKQCgDLYC3AQEBpB4kRUA=="));
decode(StringUtils.fromBase64("Z0IAIOKQCgDLYC3AQEBpB4kRUA=="));
decode(StringUtils.fromBase64("Z0IAHuNQFAe2AtwEBAaQeJEV"));
}
static int pos;
static byte[] data;
private static void decode(byte[] data) {
try {
System.out.println();
System.out.println(StringUtils.toHex(data));
System.out.println(StringUtils.toBin(data, 0, data.length, true));
System.out.println();
pos = 0;
T.data = data;
int profile_idc = getU(8);
int constraint_set0_flag = getU(1);
int constraint_set1_flag = getU(1);
int constraint_set2_flag = getU(1);
int constraint_set3_flag = getU(1);
int reserved_zero_4bits = getU(4);
int level_idc = getU(8);
int seq_parameter_set_id = uev();
int log2_max_frame_num_minus4 = uev();
int pict_order_cnt_type = uev();
System.out.println("pict_order_cnt_type=" + pict_order_cnt_type);
if (pict_order_cnt_type == 0) {
uev();
} else if (pict_order_cnt_type == 1) {
getU(1);
sev();
sev();
int n = uev();
System.out.println("n*sev, n=" + n);
for (int i = 0; i < n; i++)
sev();
}
int num_ref_frames = uev();
getU(1);
int pic_width = (uev() + 1) * 16;
int pic_height = (uev() + 1) * 16;
int frame_mbs_only_flag = getU(1);
System.out.println(pic_width + " x " + pic_height);
} catch (Exception e) {
e.printStackTrace(System.out);
}
}
private static int ev(boolean signed) {
int bitcount = 0;
StringBuilder expGolomb = new StringBuilder();
while (getBit() == 0) {
expGolomb.append('0');
bitcount++;
}
expGolomb.append("/1");
int result = 1;
for (int i = 0; i < bitcount; i++) {
int b = getBit();
expGolomb.append(b);
result = result * 2 + b;
}
result--;
if (signed) {
result = (result + 1) / 2 * (result % 2 == 0 ? -1 : 1);
System.out.println("getSe(v) = " + (result) + " " + expGolomb);
} else {
System.out.println("getUe(v) = " + (result) + " " + expGolomb);
}
return result;
}
private static int uev() {
return ev(false);
}
private static int sev() {
return ev(true);
}
private static int getU(int bits) {
int result = 0;
for (int i = 0; i < bits; i++) {
result = result * 2 + getBit();
}
System.out.println("getU(" + bits + ") = " + result);
return result;
}
private static int getBit() {
int mask = 1 << (7 - (pos & 7));
int idx = pos >> 3;
pos++;
return ((data[idx] & mask) == 0) ? 0 : 1;
}
失败案例的输出：
67420020E2900A00CB602DC040406907891150
01100111 01000010 00000000 00100000 11100010 10010000 00001010 00000000 11001011 01100000 00101101 11000000 01000000 01000000 01101001 00000111 10001001 00010001 01010000
getU(8) = 103
getU(1) = 0
getU(1) = 1
getU(1) = 0
getU(1) = 0
getU(4) = 2 << shouldn't this be 0 ? is same with correct parsing!
getU(8) = 0
getUe(v) = 3 00/100
getUe(v) = 13 000/1110 << log2_max_frame_num_minus4 shall be 0-12, inclusive.
getUe(v) = 4 00/101
pict_order_cnt_type=4 << pic_order_cnt_type shall be 0-2, inclusive.
getUe(v) = 3 00/100
getU(1) = 0
getUe(v) = 39 00000/101000
getUe(v) = 100 000000/1100101
getU(1) = 1
640 x 1616
答案 0 :(得分：2)
也许不是你要求的，但看一下参考实现，看看他们是如何解析的......
从http://www.w6rz.net/h264_parse.zip下载h.264解析器（来自此主题@ doom9 http://forum.doom9.org/archive/index.php/t-133070.html）
这应该让你开始。 BTW比特流在附录中描述。 B.在规格中。从国际电联http://www.itu.int/rec/T-REC-H.264-201003-I/en
下载答案 1 :(得分：2)
代码确实存在错误（实际上有三个）。
forbidden_bit（1位），nal_ref_idc（2位）和nal_unit_type（5位，值应为7到表示SPS单位。constraint_set#_flag而不是3（占错误3中描述的两位）。reserved_zero_#bits的数量为2。我想这可能在过去有所不同，但我不确定。所以我对解码方法进行了一些修改，并提出了适用于我的这个版本（顺便说一句，我的类叫做H264Parser，因此语句H264Parser.data = data;）：
private static void decode(byte[] data) {
try {
System.out.println();
System.out.println(StringUtils.toHex(data));
System.out.println(StringUtils.toBin(data, 0, data.length, true));
System.out.println();
pos = 0;
H264Parser.data = data;
int forbidden_zero_bit = getU(1);
System.out.println("forbidden_zero_bit " + forbidden_zero_bit);
int nal_ref_idc = getU(2);
int nal_unit_type = getU(5);
System.out.println("nal_unit_type (should be 7 for SPS) " + nal_unit_type);
//END of NAL_header
//Start of SPS data
int profile_idc = getU(8);
int constraint_set0_flag = getU(1);
int constraint_set1_flag = getU(1);
int constraint_set2_flag = getU(1);
int constraint_set3_flag = getU(1);
int constraint_set4_flag = getU(1);
int constraint_set5_flag = getU(1);
//The current version of the spec states that there are two reserved bits
int reserved_zero_2bits = getU(2);
System.out.println("reserved_zero_2bits" + reserved_zero_2bits);
int level_idc = getU(8);
int seq_parameter_set_id = uev();
int log2_max_frame_num_minus4 = uev();
int pict_order_cnt_type = uev();
System.out.println("pict_order_cnt_type=" + pict_order_cnt_type);
if (pict_order_cnt_type == 0) {
uev();
} else if (pict_order_cnt_type == 1) {
getU(1);
sev();
sev();
int n = uev();
System.out.println("n*sev, n=" + n);
for (int i = 0; i < n; i++)
sev();
}
int num_ref_frames = uev();
getU(1);
int pic_width = (uev() + 1) * 16;
int pic_height = (uev() + 1) * 16;
int frame_mbs_only_flag = getU(1);
System.out.println(pic_width + " x " + pic_height);
} catch (Exception e) {
e.printStackTrace(System.out);
}
}
答案 2 :(得分：0)
您的代码中有错误，您应该丢弃第一个字节，即NAL单位类型：
67 - NAL unit type ( SPS )
42 - Profile Idc ( Baseline profile in your case )
00 - reserved zero
29 - level ( 41 )
e2 - SPS id ( 0 ), max frame num - 4 ( 0 ), POC type ( 0 ),
90 - uev ( 5 ), num ref frames ( 1 ), u ( 0 )
etc
您实际上可以使用JCodec类https://github.com/jcodec/jcodec/blob/master/src/main/java/org/jcodec/codecs/h264/io/model/SeqParameterSet.java作为开箱即用的SPS解析例程。
答案 3 :(得分：0)
如果是某些配置文件，您还应该在seq_parameter_set_id之后读取比例矩阵：
int seq_parameter_set_id = uev();
if (profile_idc == 100 || profile_idc == 110 ||
profile_idc == 122 || profile_idc == 244 || profile_idc == 44 ||
profile_idc == 83 || profile_idc == 86 || profile_idc == 118 ||
profile_idc == 128) {
int chroma_format_idc = uev();
if( chroma_format_idc == 3 ){
int separate_colour_plane_flag = getU(1);
}
int bit_depth_luma_minus8 = uev();
int bit_depth_chroma_minus8 = uev();
int qpprime_y_zero_transform_bypass_flag = getU(1);
int seq_scaling_matrix_present_flag = getU(1);
if( seq_scaling_matrix_present_flag == 1) {
int count = (chroma_format_idc != 3) ? 8 : 12;
for (int i = 0; i <count; i++) {
int seq_scaling_list_present_flag_i_ = getU(1);
if (seq_scaling_list_present_flag_i_ == 1) {
if (i < 6)
scaling_list(16);
else
scaling_list(64);
}
}
}
}
int log2_max_frame_num_minus4 = uev();
其中缩放列表定义为folows：
int[] scaling_list(int sizeOfScalingList){
int lastScale = 8;
int nextScale = 8;
int delta_scale;
boolean useDefaultScalingMatrixFlag;
int[] scalingList = new int[sizeOfScalingList];
for(int j = 0; j < sizeOfScalingList; j++ ) {
if( nextScale != 0 ) {
delta_scale = sev();
nextScale = ( lastScale + delta_scale + 256 ) % 256;
useDefaultScalingMatrixFlag = ( j == 0 && nextScale == 0 );
}
scalingList[ j ] = ( nextScale == 0 ) ? lastScale : nextScale;
lastScale = scalingList[ j ];
}
return scalingList;
}