static int asf_read_header(AVFormatContext *s)
{
    ASFContext *asf = s->priv_data;
    ff_asf_guid g;
    AVIOContext *pb = s->pb;
    int i;
    int64_t gsize;

    ff_get_guid(pb, &g);
    if (ff_guidcmp(&g, &ff_asf_header))
        return AVERROR_INVALIDDATA;
    avio_rl64(pb);
    avio_rl32(pb);
    avio_r8(pb);
    avio_r8(pb);
    memset(&asf->asfid2avid, -1, sizeof(asf->asfid2avid));

    for (i = 0; i<128; i++)
        asf->streams[i].stream_language_index = 128; // invalid stream index means no language info

    for (;;) {
        uint64_t gpos = avio_tell(pb);
        int ret = 0;
        ff_get_guid(pb, &g);
        gsize = avio_rl64(pb);
        print_guid(&g);
        if (!ff_guidcmp(&g, &ff_asf_data_header)) {
            asf->data_object_offset = avio_tell(pb);
            /* If not streaming, gsize is not unlimited (how?),
             * and there is enough space in the file.. */
            if (!(asf->hdr.flags & 0x01) && gsize >= 100)
                asf->data_object_size = gsize - 24;
            else
                asf->data_object_size = (uint64_t)-1;
            break;
        }
        if (gsize < 24)
            return AVERROR_INVALIDDATA;
        if (!ff_guidcmp(&g, &ff_asf_file_header)) {
            ret = asf_read_file_properties(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_stream_header)) {
            ret = asf_read_stream_properties(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_comment_header)) {
            asf_read_content_desc(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_language_guid)) {
            asf_read_language_list(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_extended_content_header)) {
            asf_read_ext_content_desc(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_metadata_header)) {
            asf_read_metadata(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_metadata_library_header)) {
            asf_read_metadata(s, gsize);
        } else if (!ff_guidcmp(&g, &ff_asf_ext_stream_header)) {
            asf_read_ext_stream_properties(s, gsize);

            // there could be an optional stream properties object to follow
            // if so the next iteration will pick it up
            continue;
        } else if (!ff_guidcmp(&g, &ff_asf_head1_guid)) {
            ff_get_guid(pb, &g);
            avio_skip(pb, 6);
            continue;
        } else if (!ff_guidcmp(&g, &ff_asf_marker_header)) {
            asf_read_marker(s, gsize);
        } else if (avio_feof(pb)) {
            return AVERROR_EOF;
        } else {
            if (!s->keylen) {
                if (!ff_guidcmp(&g, &ff_asf_content_encryption)) {
                    unsigned int len;
                    AVPacket pkt;
                    av_log(s, AV_LOG_WARNING,
                           "DRM protected stream detected, decoding will likely fail!\n");
                    len= avio_rl32(pb);
                    av_log(s, AV_LOG_DEBUG, "Secret data:\n");

                    if ((ret = av_get_packet(pb, &pkt, len)) < 0)
                        return ret;
                    av_hex_dump_log(s, AV_LOG_DEBUG, pkt.data, pkt.size);
                    av_packet_unref(&pkt);
                    len= avio_rl32(pb);
                    get_tag(s, "ASF_Protection_Type", -1, len, 32);
                    len= avio_rl32(pb);
                    get_tag(s, "ASF_Key_ID", -1, len, 32);
                    len= avio_rl32(pb);
                    get_tag(s, "ASF_License_URL", -1, len, 32);
                } else if (!ff_guidcmp(&g, &ff_asf_ext_content_encryption)) {
                    av_log(s, AV_LOG_WARNING,
                           "Ext DRM protected stream detected, decoding will likely fail!\n");
                    av_dict_set(&s->metadata, "encryption", "ASF Extended Content Encryption", 0);
                } else if (!ff_guidcmp(&g, &ff_asf_digital_signature)) {
                    av_log(s, AV_LOG_INFO, "Digital signature detected!\n");
                }
            }
        }
        if (ret < 0)
            return ret;

        if (avio_tell(pb) != gpos + gsize)
            av_log(s, AV_LOG_DEBUG,
                   "gpos mismatch our pos=%"PRIu64", end=%"PRId64"\n",
                   avio_tell(pb) - gpos, gsize);
        avio_seek(pb, gpos + gsize, SEEK_SET);
    }
    ff_get_guid(pb, &g);
    avio_rl64(pb);
    avio_r8(pb);
    avio_r8(pb);
    if (avio_feof(pb))
        return AVERROR_EOF;
    asf->data_offset      = avio_tell(pb);
    asf->packet_size_left = 0;

    for (i = 0; i < 128; i++) {
        int stream_num = asf->asfid2avid[i];
        if (stream_num >= 0) {
            AVStream *st = s->streams[stream_num];
            if (!st->codecpar->bit_rate)
                st->codecpar->bit_rate = asf->stream_bitrates[i];
            if (asf->dar[i].num > 0 && asf->dar[i].den > 0) {
                av_reduce(&st->sample_aspect_ratio.num,
                          &st->sample_aspect_ratio.den,
                          asf->dar[i].num, asf->dar[i].den, INT_MAX);
            } else if ((asf->dar[0].num > 0) && (asf->dar[0].den > 0) &&
                       // Use ASF container value if the stream doesn't set AR.
                       (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO))
                av_reduce(&st->sample_aspect_ratio.num,
                          &st->sample_aspect_ratio.den,
                          asf->dar[0].num, asf->dar[0].den, INT_MAX);

            av_log(s, AV_LOG_TRACE, "i=%d, st->codecpar->codec_type:%d, asf->dar %d:%d sar=%d:%d\n",
                    i, st->codecpar->codec_type, asf->dar[i].num, asf->dar[i].den,
                    st->sample_aspect_ratio.num, st->sample_aspect_ratio.den);

            // copy and convert language codes to the frontend
            if (asf->streams[i].stream_language_index < 128) {
                const char *rfc1766 = asf->stream_languages[asf->streams[i].stream_language_index];
                if (rfc1766 && strlen(rfc1766) > 1) {
                    const char primary_tag[3] = { rfc1766[0], rfc1766[1], '\0' }; // ignore country code if any
                    const char *iso6392       = ff_convert_lang_to(primary_tag,
                                                                   AV_LANG_ISO639_2_BIBL);
                    if (iso6392)
                        av_dict_set(&st->metadata, "language", iso6392, 0);
                }
            }
        }
    }

    ff_metadata_conv(&s->metadata, NULL, ff_asf_metadata_conv);

    return 0;
}