static const uint8_t *avc_mp4_find_startcode(const uint8_t *start, const uint8_t *end, int nal_length_size) { int res = 0; if (end - start < nal_length_size) return NULL; while (nal_length_size--) res = (res << 8) | *start++; if (start + res > end || res < 0 || start + res < start) return NULL; return start + res; }