static int matroska_probe(AVProbeData *p) { uint64_t total = 0; int len_mask = 0x80, size = 1, n = 1, i; /* EBML header? */ if (AV_RB32(p->buf) != EBML_ID_HEADER) return 0; /* length of header */ total = p->buf[4]; while (size <= 8 && !(total & len_mask)) { size++; len_mask >>= 1; } if (size > 8) return 0; total &= (len_mask - 1); while (n < size) total = (total << 8) | p->buf[4 + n++]; /* Does the probe data contain the whole header? */ if (p->buf_size < 4 + size + total) return 0; /* The header should contain a known document type. For now, * we don't parse the whole header but simply check for the * availability of that array of characters inside the header. * Not fully fool-proof, but good enough. */ for (i = 0; i < FF_ARRAY_ELEMS(matroska_doctypes); i++) { int probelen = strlen(matroska_doctypes[i]); for (n = 4+size; n <= 4+size+total-probelen; n++) if (!memcmp(p->buf+n, matroska_doctypes[i], probelen)) return AVPROBE_SCORE_MAX; } // probably valid EBML header but no recognized doctype return AVPROBE_SCORE_MAX/2; }