ffm.c

ffmpeg源码分析

    pos_min = 0;
    pos_max = ffm->file_size - 2 * FFM_PACKET_SIZE;

    pts_start = get_pts(s, pos_min);

    pts = get_pts(s, pos_max);

    if (pts - 100000 > pts_start)
        goto end;

    ffm->write_index = FFM_PACKET_SIZE;

    pts_start = get_pts(s, pos_min);

    pts = get_pts(s, pos_max);

    if (pts - 100000 <= pts_start) {
        while (1) {
            offset_t newpos;
            int64_t newpts;

            newpos = ((pos_max + pos_min) / (2 * FFM_PACKET_SIZE)) * FFM_PACKET_SIZE;

            if (newpos == pos_min)
                break;

            newpts = get_pts(s, newpos);

            if (newpts - 100000 <= pts) {
                pos_max = newpos;
                pts = newpts;
            } else {
                pos_min = newpos;
            }
        }
        ffm->write_index += pos_max;
    }

    //printf("Adjusted write index from %lld to %lld: pts=%0.6f\n", orig_write_index, ffm->write_index, pts / 1000000.);
    //printf("pts range %0.6f - %0.6f\n", get_pts(s, 0) / 1000000. , get_pts(s, ffm->file_size - 2 * FFM_PACKET_SIZE) / 1000000. );

 end:
    url_fseek(pb, ptr, SEEK_SET);
}


static int ffm_read_header(AVFormatContext *s, AVFormatParameters *ap)
{
    FFMContext *ffm = s->priv_data;
    AVStream *st;
    FFMStream *fst;
    ByteIOContext *pb = &s->pb;
    AVCodecContext *codec;
    int i, nb_streams;
    uint32_t tag;

    /* header */
    tag = get_le32(pb);
    if (tag != MKTAG('F', 'F', 'M', '1'))
        goto fail;
    ffm->packet_size = get_be32(pb);
    if (ffm->packet_size != FFM_PACKET_SIZE)
        goto fail;
    ffm->write_index = get_be64(pb);
    /* get also filesize */
    if (!url_is_streamed(pb)) {
        ffm->file_size = url_fsize(pb);
        adjust_write_index(s);
    } else {
        ffm->file_size = (uint64_t_C(1) << 63) - 1;
    }

    nb_streams = get_be32(pb);
    get_be32(pb); /* total bitrate */
    /* read each stream */
    for(i=0;i<nb_streams;i++) {
        char rc_eq_buf[128];

        st = av_new_stream(s, 0);
        if (!st)
            goto fail;
        fst = av_mallocz(sizeof(FFMStream));
        if (!fst)
            goto fail;
        s->streams[i] = st;

        av_set_pts_info(st, 64, 1, 1000000);

        st->priv_data = fst;

        codec = st->codec;
        /* generic info */
        codec->codec_id = get_be32(pb);
        codec->codec_type = get_byte(pb); /* codec_type */
        codec->bit_rate = get_be32(pb);
        st->quality = get_be32(pb);
        codec->flags = get_be32(pb);
        codec->flags2 = get_be32(pb);
        codec->debug = get_be32(pb);
        /* specific info */
        switch(codec->codec_type) {
        case CODEC_TYPE_VIDEO:
            codec->time_base.num = get_be32(pb);
            codec->time_base.den = get_be32(pb);
            codec->width = get_be16(pb);
            codec->height = get_be16(pb);
            codec->gop_size = get_be16(pb);
            codec->pix_fmt = get_be32(pb);
            codec->qmin = get_byte(pb);
            codec->qmax = get_byte(pb);
            codec->max_qdiff = get_byte(pb);
            codec->qcompress = get_be16(pb) / 10000.0;
            codec->qblur = get_be16(pb) / 10000.0;
            codec->bit_rate_tolerance = get_be32(pb);
            codec->rc_eq = av_strdup(get_strz(pb, rc_eq_buf, sizeof(rc_eq_buf)));
            codec->rc_max_rate = get_be32(pb);
            codec->rc_min_rate = get_be32(pb);
            codec->rc_buffer_size = get_be32(pb);
            codec->i_quant_factor = av_int2dbl(get_be64(pb));
            codec->b_quant_factor = av_int2dbl(get_be64(pb));
            codec->i_quant_offset = av_int2dbl(get_be64(pb));
            codec->b_quant_offset = av_int2dbl(get_be64(pb));
            codec->dct_algo = get_be32(pb);
            codec->strict_std_compliance = get_be32(pb);
            codec->max_b_frames = get_be32(pb);
            codec->luma_elim_threshold = get_be32(pb);
            codec->chroma_elim_threshold = get_be32(pb);
            codec->mpeg_quant = get_be32(pb);
            codec->intra_dc_precision = get_be32(pb);
            codec->me_method = get_be32(pb);
            codec->mb_decision = get_be32(pb);
            codec->nsse_weight = get_be32(pb);
            codec->frame_skip_cmp = get_be32(pb);
            codec->rc_buffer_aggressivity = av_int2dbl(get_be64(pb));
            break;
        case CODEC_TYPE_AUDIO:
            codec->sample_rate = get_be32(pb);
            codec->channels = get_le16(pb);
            codec->frame_size = get_le16(pb);
            break;
        default:
            goto fail;
        }

    }

    /* get until end of block reached */
    while ((url_ftell(pb) % ffm->packet_size) != 0)
        get_byte(pb);

    /* init packet demux */
    ffm->packet_ptr = ffm->packet;
    ffm->packet_end = ffm->packet;
    ffm->frame_offset = 0;
    ffm->pts = 0;
    ffm->read_state = READ_HEADER;
    ffm->first_packet = 1;
    return 0;
 fail:
    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];
        if (st) {
            av_freep(&st->priv_data);
            av_free(st);
        }
    }
    return -1;
}

/* return < 0 if eof */
static int ffm_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    int size;
    FFMContext *ffm = s->priv_data;
    int duration;

    switch(ffm->read_state) {
    case READ_HEADER:
        if (!ffm_is_avail_data(s, FRAME_HEADER_SIZE)) {
            return -EAGAIN;
        }
#if 0
        printf("pos=%08Lx spos=%Lx, write_index=%Lx size=%Lx\n",
               url_ftell(&s->pb), s->pb.pos, ffm->write_index, ffm->file_size);
#endif
        if (ffm_read_data(s, ffm->header, FRAME_HEADER_SIZE, 1) !=
            FRAME_HEADER_SIZE)
            return -EAGAIN;
#if 0
        {
            int i;
            for(i=0;i<FRAME_HEADER_SIZE;i++)
                printf("%02x ", ffm->header[i]);
            printf("\n");
        }
#endif
        ffm->read_state = READ_DATA;
        /* fall thru */
    case READ_DATA:
        size = (ffm->header[2] << 16) | (ffm->header[3] << 8) | ffm->header[4];
        if (!ffm_is_avail_data(s, size)) {
            return -EAGAIN;
        }

        duration = (ffm->header[5] << 16) | (ffm->header[6] << 8) | ffm->header[7];

        av_new_packet(pkt, size);
        pkt->stream_index = ffm->header[0];
        pkt->pos = url_ftell(&s->pb);
        if (ffm->header[1] & FLAG_KEY_FRAME)
            pkt->flags |= PKT_FLAG_KEY;

        ffm->read_state = READ_HEADER;
        if (ffm_read_data(s, pkt->data, size, 0) != size) {
            /* bad case: desynchronized packet. we cancel all the packet loading */
            av_free_packet(pkt);
            return -EAGAIN;
        }
        if (ffm->first_frame_in_packet)
        {
            pkt->pts = ffm->pts;
            ffm->first_frame_in_packet = 0;
        }
        pkt->duration = duration;
        break;
    }
    return 0;
}

//#define DEBUG_SEEK

/* pos is between 0 and file_size - FFM_PACKET_SIZE. It is translated
   by the write position inside this function */
static void ffm_seek1(AVFormatContext *s, offset_t pos1)
{
    FFMContext *ffm = s->priv_data;
    ByteIOContext *pb = &s->pb;
    offset_t pos;

    pos = pos1 + ffm->write_index;
    if (pos >= ffm->file_size)
        pos -= (ffm->file_size - FFM_PACKET_SIZE);
#ifdef DEBUG_SEEK
    printf("seek to %Lx -> %Lx\n", pos1, pos);
#endif
    url_fseek(pb, pos, SEEK_SET);
}

static int64_t get_pts(AVFormatContext *s, offset_t pos)
{
    ByteIOContext *pb = &s->pb;
    int64_t pts;

    ffm_seek1(s, pos);
    url_fskip(pb, 4);
    pts = get_be64(pb);
#ifdef DEBUG_SEEK
    printf("pts=%0.6f\n", pts / 1000000.0);
#endif
    return pts;
}

/* seek to a given time in the file. The file read pointer is
   positionned at or before pts. XXX: the following code is quite
   approximative */
static int ffm_seek(AVFormatContext *s, int stream_index, int64_t wanted_pts, int flags)
{
    FFMContext *ffm = s->priv_data;
    offset_t pos_min, pos_max, pos;
    int64_t pts_min, pts_max, pts;
    double pos1;

#ifdef DEBUG_SEEK
    printf("wanted_pts=%0.6f\n", wanted_pts / 1000000.0);
#endif
    /* find the position using linear interpolation (better than
       dichotomy in typical cases) */
    pos_min = 0;
    pos_max = ffm->file_size - 2 * FFM_PACKET_SIZE;
    while (pos_min <= pos_max) {
        pts_min = get_pts(s, pos_min);
        pts_max = get_pts(s, pos_max);
        /* linear interpolation */
        pos1 = (double)(pos_max - pos_min) * (double)(wanted_pts - pts_min) /
            (double)(pts_max - pts_min);
        pos = (((int64_t)pos1) / FFM_PACKET_SIZE) * FFM_PACKET_SIZE;
        if (pos <= pos_min)
            pos = pos_min;
        else if (pos >= pos_max)
            pos = pos_max;
        pts = get_pts(s, pos);
        /* check if we are lucky */
        if (pts == wanted_pts) {
            goto found;
        } else if (pts > wanted_pts) {
            pos_max = pos - FFM_PACKET_SIZE;
        } else {
            pos_min = pos + FFM_PACKET_SIZE;
        }
    }
    pos = (flags & AVSEEK_FLAG_BACKWARD) ? pos_min : pos_max;
    if (pos > 0)
        pos -= FFM_PACKET_SIZE;
 found:
    ffm_seek1(s, pos);
    return 0;
}

#ifdef CONFIG_FFSERVER
offset_t ffm_read_write_index(int fd)
{
    uint8_t buf[8];
    offset_t pos;
    int i;

    lseek(fd, 8, SEEK_SET);
    read(fd, buf, 8);
    pos = 0;
    for(i=0;i<8;i++)
        pos |= (int64_t)buf[i] << (56 - i * 8);
    return pos;
}

void ffm_write_write_index(int fd, offset_t pos)
{
    uint8_t buf[8];
    int i;

    for(i=0;i<8;i++)
        buf[i] = (pos >> (56 - i * 8)) & 0xff;
    lseek(fd, 8, SEEK_SET);
    write(fd, buf, 8);
}

void ffm_set_write_index(AVFormatContext *s, offset_t pos, offset_t file_size)
{
    FFMContext *ffm = s->priv_data;
    ffm->write_index = pos;
    ffm->file_size = file_size;
}
#endif // CONFIG_FFSERVER

static int ffm_read_close(AVFormatContext *s)
{
    AVStream *st;
    int i;

    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];
        av_freep(&st->priv_data);
    }
    return 0;
}

static int ffm_probe(AVProbeData *p)
{
    if (p->buf_size >= 4 &&
        p->buf[0] == 'F' && p->buf[1] == 'F' && p->buf[2] == 'M' &&
        p->buf[3] == '1')
        return AVPROBE_SCORE_MAX + 1;
    return 0;
}

static AVInputFormat ffm_iformat = {
    "ffm",
    "ffm format",
    sizeof(FFMContext),
    ffm_probe,
    ffm_read_header,
    ffm_read_packet,
    ffm_read_close,
    ffm_seek,
};

#ifdef CONFIG_MUXERS
static AVOutputFormat ffm_oformat = {
    "ffm",
    "ffm format",
    "",
    "ffm",
    sizeof(FFMContext),
    /* not really used */
    CODEC_ID_MP2,
    CODEC_ID_MPEG1VIDEO,
    ffm_write_header,
    ffm_write_packet,
    ffm_write_trailer,
};
#endif //CONFIG_MUXERS

int ffm_init(void)
{
    av_register_input_format(&ffm_iformat);
#ifdef CONFIG_MUXERS
    av_register_output_format(&ffm_oformat);
#endif //CONFIG_MUXERS
    return 0;
}