utils.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

        assert(pos_limit <= pos_max);

        if(no_change==0){
            int64_t approximate_keyframe_distance= pos_max - pos_limit;
            // interpolate position (better than dichotomy)
            pos = av_rescale(target_ts - ts_min, pos_max - pos_min, ts_max - ts_min)
                + pos_min - approximate_keyframe_distance;
        }else if(no_change==1){
            // bisection, if interpolation failed to change min or max pos last time
            pos = (pos_min + pos_limit)>>1;
        }else{
            // linear search if bisection failed, can only happen if there are very few or no keframes between min/max
            pos=pos_min;
        }
        if(pos <= pos_min)
            pos= pos_min + 1;
        else if(pos > pos_limit)
            pos= pos_limit;
        start_pos= pos;

        ts = read_timestamp(s, stream_index, &pos, INT64_MAX); //may pass pos_limit instead of -1
        if(pos == pos_max)
            no_change++;
        else
            no_change=0;
#ifdef DEBUG_SEEK
av_log(s, AV_LOG_DEBUG, "%"PRId64" %"PRId64" %"PRId64" / %"PRId64" %"PRId64" %"PRId64" target:%"PRId64" limit:%"PRId64" start:%"PRId64" noc:%d\n", pos_min, pos, pos_max, ts_min, ts, ts_max, target_ts, pos_limit, start_pos, no_change);
#endif
        if(ts == AV_NOPTS_VALUE){
            av_log(s, AV_LOG_ERROR, "read_timestamp() failed in the middle\n");
            return -1;
        }
        assert(ts != AV_NOPTS_VALUE);
        if (target_ts <= ts) {
            pos_limit = start_pos - 1;
            pos_max = pos;
            ts_max = ts;
        }
        if (target_ts >= ts) {
            pos_min = pos;
            ts_min = ts;
        }
    }

    pos = (flags & AVSEEK_FLAG_BACKWARD) ? pos_min : pos_max;
    ts  = (flags & AVSEEK_FLAG_BACKWARD) ?  ts_min :  ts_max;
#ifdef DEBUG_SEEK
    pos_min = pos;
    ts_min = read_timestamp(s, stream_index, &pos_min, INT64_MAX);
    pos_min++;
    ts_max = read_timestamp(s, stream_index, &pos_min, INT64_MAX);
    av_log(s, AV_LOG_DEBUG, "pos=0x%"PRIx64" %"PRId64"<=%"PRId64"<=%"PRId64"\n",
           pos, ts_min, target_ts, ts_max);
#endif
    *ts_ret= ts;
    return pos;
}

static int av_seek_frame_byte(AVFormatContext *s, int stream_index, int64_t pos, int flags){
    int64_t pos_min, pos_max;
#if 0
    AVStream *st;

    if (stream_index < 0)
        return -1;

    st= s->streams[stream_index];
#endif

    pos_min = s->data_offset;
    pos_max = url_fsize(&s->pb) - 1;

    if     (pos < pos_min) pos= pos_min;
    else if(pos > pos_max) pos= pos_max;

    url_fseek(&s->pb, pos, SEEK_SET);

#if 0
    av_update_cur_dts(s, st, ts);
#endif
    return 0;
}

static int av_seek_frame_generic(AVFormatContext *s,
                                 int stream_index, int64_t timestamp, int flags)
{
    int index;
    AVStream *st;
    AVIndexEntry *ie;

    st = s->streams[stream_index];

    index = av_index_search_timestamp(st, timestamp, flags);

    if(index < 0 || index==st->nb_index_entries-1){
        int i;
        AVPacket pkt;

        if(st->index_entries && st->nb_index_entries){
            ie= &st->index_entries[st->nb_index_entries-1];
            url_fseek(&s->pb, ie->pos, SEEK_SET);
            av_update_cur_dts(s, st, ie->timestamp);
        }else
            url_fseek(&s->pb, 0, SEEK_SET);

        for(i=0;; i++) {
            int ret = av_read_frame(s, &pkt);
            if(ret<0)
                break;
            av_free_packet(&pkt);
            if(stream_index == pkt.stream_index){
                if((pkt.flags & PKT_FLAG_KEY) && pkt.dts > timestamp)
                    break;
            }
        }
        index = av_index_search_timestamp(st, timestamp, flags);
    }
    if (index < 0)
        return -1;

    av_read_frame_flush(s);
    if (s->iformat->read_seek){
        if(s->iformat->read_seek(s, stream_index, timestamp, flags) >= 0)
            return 0;
    }
    ie = &st->index_entries[index];
    url_fseek(&s->pb, ie->pos, SEEK_SET);

    av_update_cur_dts(s, st, ie->timestamp);

    return 0;
}

int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp, int flags)
{
    int ret;
    AVStream *st;

    av_read_frame_flush(s);

    if(flags & AVSEEK_FLAG_BYTE)
        return av_seek_frame_byte(s, stream_index, timestamp, flags);

    if(stream_index < 0){
        stream_index= av_find_default_stream_index(s);
        if(stream_index < 0)
            return -1;

        st= s->streams[stream_index];
       /* timestamp for default must be expressed in AV_TIME_BASE units */
        timestamp = av_rescale(timestamp, st->time_base.den, AV_TIME_BASE * (int64_t)st->time_base.num);
    }
    st= s->streams[stream_index];

    /* first, we try the format specific seek */
    if (s->iformat->read_seek)
        ret = s->iformat->read_seek(s, stream_index, timestamp, flags);
    else
        ret = -1;
    if (ret >= 0) {
        return 0;
    }

    if(s->iformat->read_timestamp)
        return av_seek_frame_binary(s, stream_index, timestamp, flags);
    else
        return av_seek_frame_generic(s, stream_index, timestamp, flags);
}

/*******************************************************/

/**
 * Returns TRUE if the stream has accurate duration in any stream.
 *
 * @return TRUE if the stream has accurate duration for at least one component.
 */
static int av_has_duration(AVFormatContext *ic)
{
    int i;
    AVStream *st;

    for(i = 0;i < ic->nb_streams; i++) {
        st = ic->streams[i];
        if (st->duration != AV_NOPTS_VALUE)
            return 1;
    }
    return 0;
}

/**
 * Estimate the stream timings from the one of each components.
 *
 * Also computes the global bitrate if possible.
 */
static void av_update_stream_timings(AVFormatContext *ic)
{
    int64_t start_time, start_time1, end_time, end_time1;
    int64_t duration, duration1;
    int i;
    AVStream *st;

    start_time = INT64_MAX;
    end_time = INT64_MIN;
    duration = INT64_MIN;
    for(i = 0;i < ic->nb_streams; i++) {
        st = ic->streams[i];
        if (st->start_time != AV_NOPTS_VALUE) {
            start_time1= av_rescale_q(st->start_time, st->time_base, AV_TIME_BASE_Q);
            if (start_time1 < start_time)
                start_time = start_time1;
            if (st->duration != AV_NOPTS_VALUE) {
                end_time1 = start_time1
                          + av_rescale_q(st->duration, st->time_base, AV_TIME_BASE_Q);
                if (end_time1 > end_time)
                    end_time = end_time1;
            }
        }
        if (st->duration != AV_NOPTS_VALUE) {
            duration1 = av_rescale_q(st->duration, st->time_base, AV_TIME_BASE_Q);
            if (duration1 > duration)
                duration = duration1;
        }
    }
    if (start_time != INT64_MAX) {
        ic->start_time = start_time;
        if (end_time != INT64_MIN) {
            if (end_time - start_time > duration)
                duration = end_time - start_time;
        }
    }
    if (duration != INT64_MIN) {
        ic->duration = duration;
        if (ic->file_size > 0) {
            /* compute the bit rate */
            ic->bit_rate = (double)ic->file_size * 8.0 * AV_TIME_BASE /
                (double)ic->duration;
        }
    }
}

static void fill_all_stream_timings(AVFormatContext *ic)
{
    int i;
    AVStream *st;

    av_update_stream_timings(ic);
    for(i = 0;i < ic->nb_streams; i++) {
        st = ic->streams[i];
        if (st->start_time == AV_NOPTS_VALUE) {
            if(ic->start_time != AV_NOPTS_VALUE)
                st->start_time = av_rescale_q(ic->start_time, AV_TIME_BASE_Q, st->time_base);
            if(ic->duration != AV_NOPTS_VALUE)
                st->duration = av_rescale_q(ic->duration, AV_TIME_BASE_Q, st->time_base);
        }
    }
}

static void av_estimate_timings_from_bit_rate(AVFormatContext *ic)
{
    int64_t filesize, duration;
    int bit_rate, i;
    AVStream *st;

    /* if bit_rate is already set, we believe it */
    if (ic->bit_rate == 0) {
        bit_rate = 0;
        for(i=0;i<ic->nb_streams;i++) {
            st = ic->streams[i];
            bit_rate += st->codec->bit_rate;
        }
        ic->bit_rate = bit_rate;
    }

    /* if duration is already set, we believe it */
    if (ic->duration == AV_NOPTS_VALUE &&
        ic->bit_rate != 0 &&
        ic->file_size != 0)  {
        filesize = ic->file_size;
        if (filesize > 0) {
            for(i = 0; i < ic->nb_streams; i++) {
                st = ic->streams[i];
                duration= av_rescale(8*filesize, st->time_base.den, ic->bit_rate*(int64_t)st->time_base.num);
                if (st->duration == AV_NOPTS_VALUE)
                    st->duration = duration;
            }
        }
    }
}

#define DURATION_MAX_READ_SIZE 250000

/* only usable for MPEG-PS streams */
static void av_estimate_timings_from_pts(AVFormatContext *ic, offset_t old_offset)
{
    AVPacket pkt1, *pkt = &pkt1;
    AVStream *st;
    int read_size, i, ret;
    int64_t end_time;
    int64_t filesize, offset, duration;

    /* free previous packet */
    if (ic->cur_st && ic->cur_st->parser)
        av_free_packet(&ic->cur_pkt);
    ic->cur_st = NULL;

    /* flush packet queue */
    flush_packet_queue(ic);

    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if (st->parser) {
            av_parser_close(st->parser);
            st->parser= NULL;
        }
    }

    /* we read the first packets to get the first PTS (not fully
       accurate, but it is enough now) */
    url_fseek(&ic->pb, 0, SEEK_SET);
    read_size = 0;
    for(;;) {
        if (read_size >= DURATION_MAX_READ_SIZE)
            break;
        /* if all info is available, we can stop */
        for(i = 0;i < ic->nb_streams; i++) {
            st = ic->streams[i];
            if (st->start_time == AV_NOPTS_VALUE)
                break;
        }
        if (i == ic->nb_streams)
            break;

        ret = av_read_packet(ic, pkt);
        if (ret != 0)
            break;
        read_size += pkt->size;
        st = ic->streams[pkt->stream_index];
        if (pkt->pts != AV_NOPTS_VALUE) {
            if (st->start_time == AV_NOPTS_VALUE)
                st->start_time = pkt->pts;
        }
        av_free_packet(pkt);
    }

    /* estimate the end time (duration) */
    /* XXX: may need to support wrapping */
    filesize = ic->file_size;
    offset = filesize - DURATION_MAX_READ_SIZE;
    if (offset < 0)
        offset = 0;

    url_fseek(&ic->pb, offset, SEEK_SET);
    read_size = 0;
    for(;;) {
        if (read_size >= DURATION_MAX_READ_SIZE)
            break;

        ret = av_read_packet(ic, pkt);
        if (ret != 0)
            break;
        read_size += pkt->size;
        st = ic->streams[pkt->stream_index];
        if (pkt->pts != AV_NOPTS_VALUE &&
            st->start_time != AV_NOPTS_VALUE) {
            end_time = pkt->pts;
            duration = end_time - st->start_time;
            if (duration > 0) {
                if (st->duration == AV_NOPTS_VALUE ||
                    st->duration < duration)
                    st->duration = duration;
            }
        }
        av_free_packet(pkt);
    }

    fill_all_stream_timings(ic);

    url_fseek(&ic->pb, old_offset, SEEK_SET);
    for(i=0; i<ic->nb_streams; i++){
        st= ic->streams[i];
        st->cur_dts= st->first_dts;
        st->last_IP_pts = AV_NOPTS_VALUE;
    }
}

static void av_estimate_timings(AVFormatContext *ic, offset_t old_offset)
{
    int64_t file_size;

    /* get the file size, if possible */
    if (ic->iformat->flags & AVFMT_NOFILE) {
        file_size = 0;
    } else {
        file_size = url_fsize(&ic->pb);
        if (file_size < 0)
            file_size = 0;
    }
    ic->file_size = file_size;