gxf.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

                           i * (uint64_t)fields_per_map + 1, 0, 0, 0);
    url_fskip(pb, pkt_len);
}

static int gxf_header(AVFormatContext *s, AVFormatParameters *ap) {
    ByteIOContext *pb = &s->pb;
    pkt_type_t pkt_type;
    int map_len;
    int len;
    AVRational main_timebase = {0, 0};
    st_info_t si;
    int i;
    if (!parse_packet_header(pb, &pkt_type, &map_len) || pkt_type != PKT_MAP) {
        av_log(s, AV_LOG_ERROR, "GXF: map packet not found\n");
        return 0;
    }
    map_len -= 2;
    if (get_byte(pb) != 0x0e0 || get_byte(pb) != 0xff) {
        av_log(s, AV_LOG_ERROR, "GXF: unknown version or invalid map preamble\n");
        return 0;
    }
    map_len -= 2;
    len = get_be16(pb); // length of material data section
    if (len > map_len) {
        av_log(s, AV_LOG_ERROR, "GXF: material data longer than map data\n");
        return 0;
    }
    map_len -= len;
    gxf_material_tags(pb, &len, &si);
    url_fskip(pb, len);
    map_len -= 2;
    len = get_be16(pb); // length of track description
    if (len > map_len) {
        av_log(s, AV_LOG_ERROR, "GXF: track description longer than map data\n");
        return 0;
    }
    map_len -= len;
    while (len > 0) {
        int track_type, track_id, track_len;
        AVStream *st;
        int idx;
        len -= 4;
        track_type = get_byte(pb);
        track_id = get_byte(pb);
        track_len = get_be16(pb);
        len -= track_len;
        gxf_track_tags(pb, &track_len, &si);
        url_fskip(pb, track_len);
        if (!(track_type & 0x80)) {
           av_log(s, AV_LOG_ERROR, "GXF: invalid track type %x\n", track_type);
           continue;
        }
        track_type &= 0x7f;
        if ((track_id & 0xc0) != 0xc0) {
           av_log(s, AV_LOG_ERROR, "GXF: invalid track id %x\n", track_id);
           continue;
        }
        track_id &= 0x3f;
        idx = get_sindex(s, track_id, track_type);
        if (idx < 0) continue;
        st = s->streams[idx];
        if (!main_timebase.num || !main_timebase.den) {
            main_timebase.num = si.frames_per_second.den;
            main_timebase.den = si.frames_per_second.num * si.fields_per_frame;
        }
        st->start_time = si.first_field;
        if (si.first_field != AV_NOPTS_VALUE && si.last_field != AV_NOPTS_VALUE)
            st->duration = si.last_field - si.first_field;
    }
    if (len < 0)
        av_log(s, AV_LOG_ERROR, "GXF: invalid track description length specified\n");
    if (map_len)
        url_fskip(pb, map_len);
    if (!parse_packet_header(pb, &pkt_type, &len)) {
        av_log(s, AV_LOG_ERROR, "GXF: sync lost in header\n");
        return -1;
    }
    if (pkt_type == PKT_FLT) {
        gxf_read_index(s, len);
        if (!parse_packet_header(pb, &pkt_type, &len)) {
            av_log(s, AV_LOG_ERROR, "GXF: sync lost in header\n");
            return -1;
        }
    }
    if (pkt_type == PKT_UMF) {
        if (len >= 0x39) {
            AVRational fps;
            len -= 0x39;
            url_fskip(pb, 5); // preamble
            url_fskip(pb, 0x30); // payload description
            fps = fps_umf2avr(get_le32(pb));
            if (!main_timebase.num || !main_timebase.den) {
                // this may not always be correct, but simply the best we can get
                main_timebase.num = fps.den;
                main_timebase.den = fps.num;
            }
        } else
            av_log(s, AV_LOG_INFO, "GXF: UMF packet too short\n");
    } else
        av_log(s, AV_LOG_INFO, "GXF: UMF packet missing\n");
    url_fskip(pb, len);
    if (!main_timebase.num || !main_timebase.den)
        main_timebase = (AVRational){1, 50}; // set some arbitrary fallback
    for (i = 0; i < s->nb_streams; i++) {
        AVStream *st = s->streams[i];
        av_set_pts_info(st, 32, main_timebase.num, main_timebase.den);
    }
    return 0;
}

#define READ_ONE() \
    { \
        if (!max_interval-- || url_feof(pb)) \
            goto out; \
        tmp = tmp << 8 | get_byte(pb); \
    }

/**
 * \brief resync the stream on the next media packet with specified properties
 * \param max_interval how many bytes to search for matching packet at most
 * \param track track id the media packet must belong to, -1 for any
 * \param timestamp minimum timestamp (== field number) the packet must have, -1 for any
 * \return timestamp of packet found
 */
static int64_t gxf_resync_media(AVFormatContext *s, uint64_t max_interval, int track, int timestamp) {
    uint32_t tmp;
    uint64_t last_pos;
    uint64_t last_found_pos = 0;
    int cur_track;
    int64_t cur_timestamp = AV_NOPTS_VALUE;
    int len;
    ByteIOContext *pb = &s->pb;
    pkt_type_t type;
    tmp = get_be32(pb);
start:
    while (tmp)
        READ_ONE();
    READ_ONE();
    if (tmp != 1)
        goto start;
    last_pos = url_ftell(pb);
    url_fseek(pb, -5, SEEK_CUR);
    if (!parse_packet_header(pb, &type, &len) || type != PKT_MEDIA) {
        url_fseek(pb, last_pos, SEEK_SET);
        goto start;
    }
    get_byte(pb);
    cur_track = get_byte(pb);
    cur_timestamp = get_be32(pb);
    last_found_pos = url_ftell(pb) - 16 - 6;
    if ((track >= 0 && track != cur_track) || (timestamp >= 0 && timestamp > cur_timestamp)) {
        url_fseek(pb, last_pos, SEEK_SET);
        goto start;
    }
out:
    if (last_found_pos)
        url_fseek(pb, last_found_pos, SEEK_SET);
    return cur_timestamp;
}

static int gxf_packet(AVFormatContext *s, AVPacket *pkt) {
    ByteIOContext *pb = &s->pb;
    pkt_type_t pkt_type;
    int pkt_len;
    while (!url_feof(pb)) {
        int track_type, track_id, ret;
        int field_nr;
        if (!parse_packet_header(pb, &pkt_type, &pkt_len)) {
            if (!url_feof(pb))
                av_log(s, AV_LOG_ERROR, "GXF: sync lost\n");
            return -1;
        }
        if (pkt_type == PKT_FLT) {
            gxf_read_index(s, pkt_len);
            continue;
        }
        if (pkt_type != PKT_MEDIA) {
            url_fskip(pb, pkt_len);
            continue;
        }
        if (pkt_len < 16) {
            av_log(s, AV_LOG_ERROR, "GXF: invalid media packet length\n");
            continue;
        }
        pkt_len -= 16;
        track_type = get_byte(pb);
        track_id = get_byte(pb);
        field_nr = get_be32(pb);
        get_be32(pb); // field information
        get_be32(pb); // "timeline" field number
        get_byte(pb); // flags
        get_byte(pb); // reserved
        // NOTE: there is also data length information in the
        // field information, it might be better to take this into account
        // as well.
        ret = av_get_packet(pb, pkt, pkt_len);
        pkt->stream_index = get_sindex(s, track_id, track_type);
        pkt->dts = field_nr;
        return ret;
    }
    return AVERROR(EIO);
}

static int gxf_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags) {
    uint64_t pos;
    uint64_t maxlen = 100 * 1024 * 1024;
    AVStream *st = s->streams[0];
    int64_t start_time = s->streams[stream_index]->start_time;
    int64_t found;
    int idx;
    if (timestamp < start_time) timestamp = start_time;
    idx = av_index_search_timestamp(st, timestamp - start_time,
                                    AVSEEK_FLAG_ANY | AVSEEK_FLAG_BACKWARD);
    if (idx < 0)
        return -1;
    pos = st->index_entries[idx].pos;
    if (idx < st->nb_index_entries - 2)
        maxlen = st->index_entries[idx + 2].pos - pos;
    maxlen = FFMAX(maxlen, 200 * 1024);
    url_fseek(&s->pb, pos, SEEK_SET);
    found = gxf_resync_media(s, maxlen, -1, timestamp);
    if (FFABS(found - timestamp) > 4)
        return -1;
    return 0;
}

static int64_t gxf_read_timestamp(AVFormatContext *s, int stream_index,
                                  int64_t *pos, int64_t pos_limit) {
    ByteIOContext *pb = &s->pb;
    int64_t res;
    url_fseek(pb, *pos, SEEK_SET);
    res = gxf_resync_media(s, pos_limit - *pos, -1, -1);
    *pos = url_ftell(pb);
    return res;
}

AVInputFormat gxf_demuxer = {
    "gxf",
    "GXF format",
    0,
    gxf_probe,
    gxf_header,
    gxf_packet,
    NULL,
    gxf_seek,
    gxf_read_timestamp,
};