utils.c

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                index++; //index points to next instead of previous entry, maybe nonexistant
                ie= &st->index_entries[index];
            }else
                assert(index==0);
                
            if(index != st->nb_index_entries){
                assert(index < st->nb_index_entries);
                memmove(entries + index + 1, entries + index, sizeof(AVIndexEntry)*(st->nb_index_entries - index));
            }
            st->nb_index_entries++;
        }else{
            if(ie->pos == pos && distance < ie->min_distance) //dont reduce the distance
                distance= ie->min_distance;
        }
    }else{
        index= st->nb_index_entries++;
        ie= &entries[index];
    }
    
    ie->pos = pos;
    ie->timestamp = timestamp;
    ie->min_distance= distance;
    ie->flags = flags;
    
    return index;
}

/* build an index for raw streams using a parser */
static void av_build_index_raw(AVFormatContext *s)
{
    AVPacket pkt1, *pkt = &pkt1;
    int ret;
    AVStream *st;

    st = s->streams[0];
    av_read_frame_flush(s);
    url_fseek(&s->pb, s->data_offset, SEEK_SET);

    for(;;) {
        ret = av_read_frame(s, pkt);
        if (ret < 0)
            break;
        if (pkt->stream_index == 0 && st->parser &&
            (pkt->flags & PKT_FLAG_KEY)) {
            int64_t dts= av_rescale(pkt->dts, st->time_base.den, AV_TIME_BASE*(int64_t)st->time_base.num);
            av_add_index_entry(st, st->parser->frame_offset, dts, 
                            0, AVINDEX_KEYFRAME);
        }
        av_free_packet(pkt);
    }
}

/* return TRUE if we deal with a raw stream (raw codec data and
   parsing needed) */
static int is_raw_stream(AVFormatContext *s)
{
    AVStream *st;

    if (s->nb_streams != 1)
        return 0;
    st = s->streams[0];
    if (!st->need_parsing)
        return 0;
    return 1;
}

/* return the largest index entry whose timestamp is <=
   wanted_timestamp */
int av_index_search_timestamp(AVStream *st, int wanted_timestamp)
{
    AVIndexEntry *entries= st->index_entries;
    int nb_entries= st->nb_index_entries;
    int a, b, m;
    int64_t timestamp;

    if (nb_entries <= 0)
        return -1;
    
    a = 0;
    b = nb_entries - 1;

    while (a < b) {
        m = (a + b + 1) >> 1;
        timestamp = entries[m].timestamp;
        if (timestamp > wanted_timestamp) {
            b = m - 1;
        } else {
            a = m;
        }
    }
    return a;
}

#define DEBUG_SEEK

/**
 * Does a binary search using av_index_search_timestamp() and AVCodec.read_timestamp().
 * this isnt supposed to be called directly by a user application, but by demuxers
 * @param target_ts target timestamp in the time base of the given stream
 * @param stream_index stream number
 */
int av_seek_frame_binary(AVFormatContext *s, int stream_index, int64_t target_ts){
    AVInputFormat *avif= s->iformat;
    int64_t pos_min, pos_max, pos, pos_limit;
    int64_t ts_min, ts_max, ts;
    int64_t start_pos;
    int index, no_change, i;
    AVStream *st;

    if (stream_index < 0)
        return -1;
    
#ifdef DEBUG_SEEK
    av_log(s, AV_LOG_DEBUG, "read_seek: %d %lld\n", stream_index, target_ts);
#endif

    ts_max=
    ts_min= AV_NOPTS_VALUE;
    pos_limit= -1; //gcc falsely says it may be uninitalized

    st= s->streams[stream_index];
    if(st->index_entries){
        AVIndexEntry *e;

        index= av_index_search_timestamp(st, target_ts);
        e= &st->index_entries[index];

        if(e->timestamp <= target_ts || e->pos == e->min_distance){
            pos_min= e->pos;
            ts_min= e->timestamp;
#ifdef DEBUG_SEEK
        av_log(s, AV_LOG_DEBUG, "using cached pos_min=0x%llx dts_min=%lld\n", 
               pos_min,ts_min);
#endif
        }else{
            assert(index==0);
        }
        index++;
        if(index < st->nb_index_entries){
            e= &st->index_entries[index];
            assert(e->timestamp >= target_ts);
            pos_max= e->pos;
            ts_max= e->timestamp;
            pos_limit= pos_max - e->min_distance;
#ifdef DEBUG_SEEK
        av_log(s, AV_LOG_DEBUG, "using cached pos_max=0x%llx pos_limit=0x%llx dts_max=%lld\n", 
               pos_max,pos_limit, ts_max);
#endif
        }
    }

    if(ts_min == AV_NOPTS_VALUE){
        pos_min = s->data_offset;
        ts_min = avif->read_timestamp(s, stream_index, &pos_min, INT64_MAX);
        if (ts_min == AV_NOPTS_VALUE)
            return -1;
    }

    if(ts_max == AV_NOPTS_VALUE){
        int step= 1024;
        pos_max = url_filesize(url_fileno(&s->pb)) - 1;
        do{
            pos_max -= step;
            ts_max = avif->read_timestamp(s, stream_index, &pos_max, pos_max + step);
            step += step;
        }while(ts_max == AV_NOPTS_VALUE && pos_max >= step);
        if (ts_max == AV_NOPTS_VALUE)
            return -1;
        
        for(;;){
            int64_t tmp_pos= pos_max + 1;
            int64_t tmp_ts= avif->read_timestamp(s, stream_index, &tmp_pos, INT64_MAX);
            if(tmp_ts == AV_NOPTS_VALUE)
                break;
            ts_max= tmp_ts;
            pos_max= tmp_pos;
        }
        pos_limit= pos_max;
    }

    no_change=0;
    while (pos_min < pos_limit) {
#ifdef DEBUG_SEEK
        av_log(s, AV_LOG_DEBUG, "pos_min=0x%llx pos_max=0x%llx dts_min=%lld dts_max=%lld\n", 
               pos_min, pos_max,
               ts_min, ts_max);
#endif
        assert(pos_limit <= pos_max);

        if(no_change==0){
            int64_t approximate_keyframe_distance= pos_max - pos_limit;
            // interpolate position (better than dichotomy)
            pos = (int64_t)((double)(pos_max - pos_min) *
                            (double)(target_ts - ts_min) /
                            (double)(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 = avif->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, "%Ld %Ld %Ld / %Ld %Ld %Ld target:%Ld limit:%Ld start:%Ld noc:%d\n", pos_min, pos, pos_max, ts_min, ts, ts_max, target_ts, pos_limit, start_pos, no_change);
#endif
        assert(ts != AV_NOPTS_VALUE);
        if (target_ts < ts) {
            pos_limit = start_pos - 1;
            pos_max = pos;
            ts_max = ts;
        } else {
            pos_min = pos;
            ts_min = ts;
            /* check if we are lucky */
            if (target_ts == ts)
                break;
        }
    }
    
    pos = pos_min;
#ifdef DEBUG_SEEK
    pos_min = pos;
    ts_min = avif->read_timestamp(s, stream_index, &pos_min, INT64_MAX);
    pos_min++;
    ts_max = avif->read_timestamp(s, stream_index, &pos_min, INT64_MAX);
    av_log(s, AV_LOG_DEBUG, "pos=0x%llx %lld<=%lld<=%lld\n", 
           pos, ts_min, target_ts, ts_max);
#endif
    /* do the seek */
    url_fseek(&s->pb, pos, SEEK_SET);

    ts= av_rescale(ts_min, AV_TIME_BASE*(int64_t)st->time_base.num, st->time_base.den);
    for(i = 0; i < s->nb_streams; i++) {
        st = s->streams[i];

        st->cur_dts = av_rescale(ts, st->time_base.den, AV_TIME_BASE*(int64_t)st->time_base.num);
    }

    return 0;
}

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

    if (!s->index_built) {
        if (is_raw_stream(s)) {
            av_build_index_raw(s);
        } else {
            return -1;
        }
        s->index_built = 1;
    }

    st = s->streams[stream_index];
    index = av_index_search_timestamp(st, timestamp);
    if (index < 0)
        return -1;

    /* now we have found the index, we can seek */
    ie = &st->index_entries[index];
    av_read_frame_flush(s);
    url_fseek(&s->pb, ie->pos, SEEK_SET);
    
    timestamp= av_rescale(ie->timestamp, AV_TIME_BASE*(int64_t)st->time_base.num, st->time_base.den);
    for(i = 0; i < s->nb_streams; i++) {
        st = s->streams[i];

        st->cur_dts = av_rescale(timestamp, st->time_base.den, AV_TIME_BASE*(int64_t)st->time_base.num);
    }

    return 0;
}

/**
 * Seek to the key frame just before the frame at timestamp
 * 'timestamp' in 'stream_index'.
 * @param stream_index If stream_index is (-1), a default
 * stream is selected
 * @param timestamp timestamp in AV_TIME_BASE units
 * @return >= 0 on success
 */
int av_seek_frame(AVFormatContext *s, int stream_index, int64_t timestamp)
{
    int ret;
    AVStream *st;
    
    av_read_frame_flush(s);
    
    if(stream_index < 0){
        stream_index= av_find_default_stream_index(s);
        if(stream_index < 0)
            return -1;
    }
    st= s->streams[stream_index];

    timestamp = av_rescale(timestamp, st->time_base.den, AV_TIME_BASE * (int64_t)st->time_base.num);

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

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

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

/* return TRUE if the stream has accurate timings for at least one component */
static int av_has_timings(AVFormatContext *ic)
{
    int i;
    AVStream *st;

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

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

    start_time = MAXINT64;
    end_time = MININT64;
    for(i = 0;i < ic->nb_streams; i++) {
        st = ic->streams[i];
        if (st->start_time != AV_NOPTS_VALUE) {
            if (st->start_time < start_time)
                start_time = st->start_time;
            if (st->duration != AV_NOPTS_VALUE) {
                end_time1 = st->start_time + st->duration;
                if (end_time1 > end_time)
                    end_time = end_time1;
            }
        }
    }
    if (start_time != MAXINT64) {
        ic->start_time = start_time;
        if (end_time != MAXINT64) {
            ic->duration = end_time - start_time;
            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) {
            st->start_time = ic->start_time;
            st->duration = ic->duration;
        }
    }
}

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) {
            duration = (int64_t)((8 * AV_TIME_BASE * (double)filesize) / (double)ic->bit_rate);
            for(i = 0; i < ic->nb_streams; i++) {
                st = ic->streams[i];
                if (st->start_time == AV_NOPTS_VALUE ||
                    st->duration == AV_NOPTS_VALUE) {
                    st->start_time = 0;
                    st->duration = duration;
                }
            }
        }
    }
}

#define DURATION_MAX_READ_SIZE 250000

/* only usable for MPEG-PS streams */
static void av_estimate_timings_from_pts(AVFormatContext *ic)
{
    AVPacket pkt1, *pkt = &pkt1;
    AVStream *st;
    int read_size, i, ret;
    int64_t start_time, end_time, end_time1;
    int64_t filesize, offset, duration;