c - 如何识别 mpegts 文件？

Question

如何识别 mpegts 文件？我从 here 复制了以下代码，并且它在很多文件上都运行良好，但他也识别出this file作为 mpegts 视频。下面是有问题的文件的开头。
这是我使用的代码:

#define MPEGTS_MIN_BUF_SIZE  1024 * 4 

static __forceinline const uint16_t av_bswap16(uint16_t x)
{
    x = (x >> 8) | (x << 8);
    return x;
}

#define AV_RB16(x) av_bswap16(x)
#define bswap16(x) ((x)>>8 | ((x)&255)<<8) // https://stackoverflow.com/a/648215/7206675

#define FFMAX(a,b) ((a) > (b) ? (a) : (b))
#define FFMAX3(a,b,c) FFMAX(FFMAX(a,b),c)
#define FFMIN(a,b) ((a) > (b) ? (b) : (a))
#define FFMIN3(a,b,c) FFMIN(FFMIN(a,b),c)

static int analyze2(const uint8_t* buf, int size, int packet_size,
    int probe)
{
    int stat[TS_MAX_PACKET_SIZE];
    int stat_all = 0;
    int i;
    int best_score = 0;

    memset(stat, 0, packet_size * sizeof(*stat));

    for (i = 0; i < size - 3; i++) 
    {
        if (buf[i] == 0x47) 
        {
            int pid = AV_RB16(buf + 1) & 0x1FFF;
            int asc = buf[i + 3] & 0x30;
            if (!probe || pid == 0x1FFF || asc) 
            {
                int x = i % packet_size;
                stat[x]++;
                stat_all++;
                if (stat[x] > best_score) 
                {
                    best_score = stat[x];
                }
            }
        }
    }

    return best_score - FFMAX(stat_all - 10 * best_score, 0) / 10;
}

/**
 * This structure contains the data a format has to probe a file.
 */
typedef struct AVProbeData {
    const char* filename;
    unsigned char* buf; /**< Buffer must have AVPROBE_PADDING_SIZE of extra allocated bytes filled with zero. */
    int buf_size;       /**< Size of buf except extra allocated bytes */
    const char* mime_type; /**< mime_type, when known. */
} AVProbeData;

#define AVPROBE_SCORE_MAX       100 ///< maximum score

static int mpegts_probe(const AVProbeData* p)
{
    const int size = p->buf_size;
    int maxscore = 0;
    int sumscore = 0;
    int i;
    int check_count = size / TS_FEC_PACKET_SIZE;
#define CHECK_COUNT 10
#define CHECK_BLOCK 100

    if (!check_count)
        return 0;

    for (i = 0; i < check_count; i += CHECK_BLOCK) {
        int left = FFMIN(check_count - i, CHECK_BLOCK);
        int score = analyze2(p->buf + TS_PACKET_SIZE * i, TS_PACKET_SIZE * left, TS_PACKET_SIZE, 1);
        int dvhs_score = analyze2(p->buf + TS_DVHS_PACKET_SIZE * i, TS_DVHS_PACKET_SIZE * left, TS_DVHS_PACKET_SIZE, 1);
        int fec_score = analyze2(p->buf + TS_FEC_PACKET_SIZE * i, TS_FEC_PACKET_SIZE * left, TS_FEC_PACKET_SIZE, 1);
        score = FFMAX3(score, dvhs_score, fec_score);
        sumscore += score;
        maxscore = FFMAX(maxscore, score);
    }

    sumscore = sumscore * CHECK_COUNT / check_count;
    maxscore = maxscore * CHECK_COUNT / CHECK_BLOCK;

    //ff_dlog(0, "TS score: %d %d\n", sumscore, maxscore);

    if (check_count > CHECK_COUNT && sumscore > 6) {
        return AVPROBE_SCORE_MAX + sumscore - CHECK_COUNT;
    }
    else if (check_count >= CHECK_COUNT && sumscore > 6) {
        return AVPROBE_SCORE_MAX / 2 + sumscore - CHECK_COUNT;
    }
    else if (check_count >= CHECK_COUNT && maxscore > 6) {
        return AVPROBE_SCORE_MAX / 2 + sumscore - CHECK_COUNT;
    }
    else if (sumscore > 6) {
        return 2;
    }
    else {
        return 0;
    }
}

int main() 
{
    BOOL IsMpegtsVideo = FALSE;
    char buf[MPEGTS_MIN_BUF_SIZE];

    ReadMyTestFile(buf);

    AVProbeData p;
    p.buf = buf;
    p.buf_size = MPEGTS_MIN_BUF_SIZE;
    int score = mpegts_probe(&p);

    IsMpegtsVideo = score > 0;

    return 0;
}

这是被错误识别为视频的文件的开头:

#ifdef TARGET_ABI32
/*
 * Linux N32 syscalls are in the range from 6000 to 6999.
 */
#define TARGET_NR_Linux                 6000
#define TARGET_NR_read                  (TARGET_NR_Linux +   0)
#define TARGET_NR_write                 (TARGET_NR_Linux +   1)
#define TARGET_NR_open                  (TARGET_NR_Linux +   2)
#define TARGET_NR_close                 (TARGET_NR_Linux +   3)
#define TARGET_NR_stat                  (TARGET_NR_Linux +   4)
#define TARGET_NR_fstat                 (TARGET_NR_Linux +   5)
#define TARGET_NR_lstat                 (TARGET_NR_Linux +   6)
#define TARGET_NR_poll                  (TARGET_NR_Linux +   7)
#define TARGET_NR_lseek                 (TARGET_NR_Linux +   8)
#define TARGET_NR_mmap                  (TARGET_NR_Linux +   9)
#define TARGET_NR_mprotect              (TARGET_NR_Linux +  10)
#define TARGET_NR_munmap                (TARGET_NR_Linux +  11)
#define TARGET_NR_brk                   (TARGET_NR_Linux +  12)
#define TARGET_NR_rt_sigaction          (TARGET_NR_Linux +  13)
#define TARGET_NR_rt_sigprocmask        (TARGET_NR_Linux +  14)
#define TARGET_NR_ioctl                 (TARGET_NR_Linux +  15)
#define TARGET_NR_pread64               (TARGET_NR_Linux +  16)
#define TARGET_NR_pwrite64              (TARGET_NR_Linux +  17)
#define TARGET_NR_readv                 (TARGET_NR_Linux +  18)
#define TARGET_NR_writev                (TARGET_NR_Linux +  19)
#define TARGET_NR_access                (TARGET_NR_Linux +  20)
#define TARGET_NR_pipe                  (TARGET_NR_Linux +  21)
#define TARGET_NR__newselect            (TARGET_NR_Linux +  22)
#define TARGET_NR_sched_yield           (TARGET_NR_Linux +  23)
#define TARGET_NR_mremap                (TARGET_NR_Linux +  24)
#define TARGET_NR_msync                 (TARGET_NR_Linux +  25)
#define TARGET_NR_mincore               (TARGET_NR_Linux +  26)
#define TARGET_NR_madvise               (TARGET_NR_Linux +  27)
#define TARGET_NR_shmget                (TARGET_NR_Linux +  28)
#define TARGET_NR_shmat                 (TARGET_NR_Linux +  29)
#define TARGET_NR_shmctl                (TARGET_NR_Linux +  30)
#define TARGET_NR_dup                   (TARGET_NR_Linux +  31)
#define TARGET_NR_dup2                  (TARGET_NR_Linux +  32)

如何改进我的代码，使其无法将上述文件识别为视频，而另一方面继续将其识别为实际上是视频的视频文件？

Answer 1

您需要查看 Pid字段 - Packet identifier flag, used to associate one packet with a set .它可以有很多有效值，但必须首先带有 PatPid 之类的值, SdtPid .
如果这些值没有出现在第一个数据包中，则可能不是视频。

public enum PidType
{
    PatPid = 0x0,
    CatPid = 0x1,
    TsDescPid = 0x2,
    NitPid = 0x10,
    SdtPid = 0x11,
    EitPid = 0x12,
    NullPid = 0x1FFF
}