static int extract_rbsp(const uint8_t *src, int length,
                        HEVCNAL *nal)
{
    int i, si, di;
    uint8_t *dst;

#define STARTCODE_TEST                                                  \
        if (i + 2 < length && src[i + 1] == 0 && src[i + 2] <= 3) {     \
            if (src[i + 2] != 3) {                                      \
                /* startcode, so we must be past the end */             \
                length = i;                                             \
            }                                                           \
            break;                                                      \
        }
#if HAVE_FAST_UNALIGNED
#define FIND_FIRST_ZERO                                                 \
        if (i > 0 && !src[i])                                           \
            i--;                                                        \
        while (src[i])                                                  \
            i++
#if HAVE_FAST_64BIT
    for (i = 0; i + 1 < length; i += 9) {
        if (!((~AV_RN64A(src + i) &
               (AV_RN64A(src + i) - 0x0100010001000101ULL)) &
              0x8000800080008080ULL))
            continue;
        FIND_FIRST_ZERO;
        STARTCODE_TEST;
        i -= 7;
    }
#else
    for (i = 0; i + 1 < length; i += 5) {
        if (!((~AV_RN32A(src + i) &
               (AV_RN32A(src + i) - 0x01000101U)) &
              0x80008080U))
            continue;
        FIND_FIRST_ZERO;
        STARTCODE_TEST;
        i -= 3;
    }
#endif /* HAVE_FAST_64BIT */
#else
    for (i = 0; i + 1 < length; i += 2) {
        if (src[i])
            continue;
        if (i > 0 && src[i - 1] == 0)
            i--;
        STARTCODE_TEST;
    }
#endif /* HAVE_FAST_UNALIGNED */

    if (i >= length - 1) { // no escaped 0
        nal->data = src;
        nal->size = length;
        return length;
    }

    av_fast_malloc(&nal->rbsp_buffer, &nal->rbsp_buffer_size,
                   length + FF_INPUT_BUFFER_PADDING_SIZE);
    if (!nal->rbsp_buffer)
        return AVERROR(ENOMEM);

    dst = nal->rbsp_buffer;

    memcpy(dst, src, i);
    si = di = i;
    while (si + 2 < length) {
        // remove escapes (very rare 1:2^22)
        if (src[si + 2] > 3) {
            dst[di++] = src[si++];
            dst[di++] = src[si++];
        } else if (src[si] == 0 && src[si + 1] == 0) {
            if (src[si + 2] == 3) { // escape
                dst[di++] = 0;
                dst[di++] = 0;
                si       += 3;

                continue;
            } else // next start code
                goto nsc;
        }

        dst[di++] = src[si++];
    }
    while (si < length)
        dst[di++] = src[si++];

nsc:
    memset(dst + di, 0, FF_INPUT_BUFFER_PADDING_SIZE);

    nal->data = dst;
    nal->size = di;
    return si;
}
static int extract_rbsp(const uint8_t *src, int length,
                        HEVCNAL *nal)
{
    int i, si, di;
    uint8_t *dst;

#define STARTCODE_TEST                                                  \
        if (i + 2 < length && src[i + 1] == 0 && src[i + 2] <= 3) {     \
            if (src[i + 2] != 3) {                                      \
                              \
                length = i;                                             \
            }                                                           \
            break;                                                      \
        }
#if HAVE_FAST_UNALIGNED
#define FIND_FIRST_ZERO                                                 \
        if (i > 0 && !src[i])                                           \
            i--;                                                        \
        while (src[i])                                                  \
            i++
#if HAVE_FAST_64BIT
    for (i = 0; i + 1 < length; i += 9) {
        if (!((~AV_RN64A(src + i) &
               (AV_RN64A(src + i) - 0x0100010001000101ULL)) &
              0x8000800080008080ULL))
            continue;
        FIND_FIRST_ZERO;
        STARTCODE_TEST;
        i -= 7;
    }
#else
    for (i = 0; i + 1 < length; i += 5) {
        if (!((~AV_RN32A(src + i) &
               (AV_RN32A(src + i) - 0x01000101U)) &
              0x80008080U))
            continue;
        FIND_FIRST_ZERO;
        STARTCODE_TEST;
        i -= 3;
    }
#endif  
#else
    for (i = 0; i + 1 < length; i += 2) {
        if (src[i])
            continue;
        if (i > 0 && src[i - 1] == 0)
            i--;
        STARTCODE_TEST;
    }
#endif  

    if (i >= length - 1) {  
        nal->data = src;
        nal->size = length;
        return length;
    }

    av_fast_malloc(&nal->rbsp_buffer, &nal->rbsp_buffer_size,
                   length + FF_INPUT_BUFFER_PADDING_SIZE);
    if (!nal->rbsp_buffer)
        return AVERROR(ENOMEM);

    dst = nal->rbsp_buffer;

    memcpy(dst, src, i);
    si = di = i;
    while (si + 2 < length) {
         
        if (src[si + 2] > 3) {
            dst[di++] = src[si++];
            dst[di++] = src[si++];
        } else if (src[si] == 0 && src[si + 1] == 0) {
            if (src[si + 2] == 3) {  
                dst[di++] = 0;
                dst[di++] = 0;
                si       += 3;

                continue;
            } else  
                goto nsc;
        }

        dst[di++] = src[si++];
    }
    while (si < length)
        dst[di++] = src[si++];

nsc:
    memset(dst + di, 0, FF_INPUT_BUFFER_PADDING_SIZE);

    nal->data = dst;
    nal->size = di;
    return si;
}