utils.c

}

#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, "unsing 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, "unsing 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 = ts;
    }

    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 = timestamp;
    }

    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;
    
    /* 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);
    

    /* 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 = av_rescale(pkt->pts, st->time_base.num * (int64_t)AV_TIME_BASE, st->time_base.den);
        }
        av_free_packet(pkt);
    }

    /* we compute the minimum start_time and use it as default */
    start_time = MAXINT64;
    for(i = 0; i < ic->nb_streams; i++) {
        st = ic->streams[i];
        if (st->start_time != AV_NOPTS_VALUE &&
            st->start_time < start_time)
            start_time = st->start_time;
    }
    if (start_time != MAXINT64)
        ic->start_time = start_time;
    
    /* 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;
        /* if all info is available, we can stop */
        for(i = 0;i < ic->nb_streams; i++) {
            st = ic->streams[i];
            if (st->duration == 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) {
            end_time = av_rescale(pkt->pts, st->time_base.num * (int64_t)AV_TIME_BASE, st->time_base.den);
            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);
    }
    
    /* estimate total duration */
    end_time = MININT64;
    for(i = 0;i < ic->nb_streams; i++) {
        st = ic->streams[i];
        if (st->duration != AV_NOPTS_VALUE) {
            end_time1 = st->start_time + st->duration;
            if (end_time1 > end_time)
                end_time = end_time1;
        }
    }
    
    /* update start_time (new stream may have been created, so we do
       it at the end */
    if (ic->start_time != AV_NOPTS_VALUE) {
        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;
        }
    }

    if (end_time != MININT64) {
        /* put dummy values for duration if needed */
        for(i = 0;i < ic->nb_streams; i++) {
            st = ic->streams[i];
            if (st->duration == AV_NOPTS_VALUE && 
                st->start_time != AV_NOPTS_VALUE)
                st->duration = end_time - st->start_time;
        }
        ic->duration = end_time - ic->start_time;
    }

    url_fseek(&ic->pb, 0, SEEK_SET);
}

static void av_estimate_timings(AVFormatContext *ic)
{
    URLContext *h;
    int64_t file_size;

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

    if (ic->iformat == &mpegps_demux) {
        /* get accurate estimate from the PTSes */
        av_estimate_timings_from_pts(ic);
    } else if (av_has_timings(ic)) {
        /* at least one components has timings - we use them for all
           the components */
        fill_all_stream_timings(ic);
    } else {
        /* less precise: use bit rate info */
        av_estimate_timings_from_bit_rate(ic);
    }
    av_update_stream_timings(ic);

#if 0
    {
        int i;
        AVStream *st;
        for(i = 0;i < ic->nb_streams; i++) {
            st = ic->streams[i];
        printf("%d: start_time: %0.3f duration: %0.3f\n", 
               i, (double)st->start_time / AV_TIME_BASE, 
               (double)st->duration / AV_TIME_BASE);
        }
        printf("stream: start_time: %0.3f duration: %0.3f bitrate=%d kb/s\n", 
               (double)ic->start_time / AV_TIME_BASE, 
               (double)ic->duration / AV_TIME_BASE,
               ic->bit_rate / 1000);
    }
#endif
}

static int has_codec_parameters(AVCodecContext *enc)
{
    int val;
    switch(enc->codec_type) {
    case CODEC_TYPE_AUDIO:
        val = enc->sample_rate;
        break;
    case CODEC_TYPE_VIDEO:
        val = enc->width;
        break;
    default:
        val = 1;
        break;
    }
    return (val != 0);
}

static int try_decode_frame(AVStream *st, const uint8_t *data, int size)
{
    int16_t *samples;
    AVCodec *codec;
    int got_picture, ret;
    AVFrame picture;
    
    codec = avcodec_find_decoder(st->codec.codec_id);
    if (!codec)
        return -1;
    ret = avcodec_open(&st->codec, codec);
    if (ret < 0)
        return ret;
    switch(st->codec.codec_type) {
    case CODEC_TYPE_VIDEO:
        ret = avcodec_decode_video(&st->codec, &picture, 
                                   &got_picture, (uint8_t *)data, size);
        break;
    case CODEC_TYPE_AUDIO:
        samples = av_malloc(AVCODEC_MAX_AUDIO_FRAME_SIZE);
        if (!samples)
            goto fail;
        ret = avcodec_decode_audio(&st->codec, samples, 
                                   &got_picture, (uint8_t *)data, size);
        av_free(samples);
        break;
    default:
        break;
    }
 fail:
    avcodec_close(&st->codec);
    return ret;
}

/* absolute maximum size we read until we abort */
#define MAX_READ_SIZE        5000000

/* maximum duration until we stop analysing the stream */
#define MAX_STREAM_DURATION  ((int)(AV_TIME_BASE * 1.0))

/**
 * Read the beginning of a media file to get stream information. This
 * is useful for file formats with no headers such as MPEG. This
 * function also compute the real frame rate in case of mpeg2 repeat
 * frame mode.
 *
 * @param ic media file handle
 * @return >=0 if OK. AVERROR_xxx if error.  
 */
int av_find_stream_info(AVFormatContext *ic)
{
    int i, count, ret, read_size;
    AVStream *st;
    AVPacket pkt1, *pkt;
    AVPacketList *pktl=NULL, **ppktl;

    count = 0;
    read_size = 0;
    ppktl = &ic->packet_buffer;
    for(;;) {
        /* check if one codec still needs to be handled */
        for(i=0;i<ic->nb_streams;i++) {
            st = ic->streams[i];
            if (!has_codec_parameters(&st->codec))
                break;
        }
        if (i == ic->nb_streams) {
            /* NOTE: if the format has no header, then we need to read
               some packets to get most of the streams, so we cannot
               stop here */
            if (!(ic->ctx_flags & AVFMTCTX_NOHEADER)) {
                /* if we found the info for all the codecs, we can stop */
                ret = count;
                break;
            }
        } else {
            /* we did not get all the codec info, but we read too much data */
            if (read_size >= MAX_READ_SIZE) {
                ret = count;
                break;
            }
        }

        /* NOTE: a new stream can be added there if no header in file
           (AVFMTCTX_NOHEADER) */
        ret = av_read_frame_internal(ic, &pkt1);
        if (ret < 0) {
            /* EOF or error */
            ret = -1; /* we could not have all the codec parameters before EOF */
            if ((ic->ctx_flags & AVFMTCTX_NOHEADER) &&
                i == ic->nb_streams)
                ret = 0;
            break;
        }

        pktl = av_mallocz(sizeof(AVPacketList));
        if (!pktl) {
            ret = AVERROR_NOMEM;
            break;
        }

        /* add the packet in the buffered packet list */
        *ppktl = pktl;
        ppktl = &pktl->next;

        pkt = &pktl->pkt;
        *pkt = pkt1;
        
        /* duplicate the packet */
        if (av_dup_packet(pkt) < 0) {
                ret = AVERROR_NOMEM;
                break;
        }

        read_size += pkt->size;

        st = ic->streams[pkt->stream_index];
        st->codec_info_duration += pkt->duration;
        if (pkt->duration != 0)
            st->codec_info_nb_frames++;

        /* if still no information, we try to open the codec and to
           decompress the frame. We try to avoid that in most cases as
           it takes longer and uses more memory. For MPEG4, we need to
           decompress for Quicktime. */
        if (!has_codec_parameters(&st->codec) &&
            (st->codec.codec_id == CODEC_ID_FLV1 ||
             st->codec.codec_id == CODEC_ID_H264 ||
             st->codec.codec_id == CODEC_ID_H263 ||
             st->codec.codec_id == CODEC_ID_VORBIS ||
             (st->codec.codec_id == CODEC_ID_MPEG4 && !st->need_parsing)))
            try_decode_frame(st, pkt->data, pkt->size);
        
        if (st->codec_info_duration >= MAX_STREAM_DURATION) {
            break;
        }
        count++;
    }

    /* set real frame rate info */
    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if (st->codec.codec_type == CODEC_TYPE_VIDEO) {
            /* compute the real frame rate for telecine */
            if ((st->codec.codec_id == CODEC_ID_MPEG1VIDEO ||
                 st->codec.codec_id == CODEC_ID_MPEG2VIDEO) &&
                st->codec.sub_id == 2) {
                if (st->codec_info_nb_frames >= 20) {
                    float coded_frame_rate, est_frame_rate;
                    est_frame_rate = ((double)st->codec_info_nb_frames * AV_TIME_BASE) / 
                        (double)st->codec_info_duration ;
                    coded_frame_rate = (double)st->codec.frame_rate /
                        (double)st->codec.frame_rate_base;
#if 0
                    printf("telecine: coded_frame_rate=%0.3f est_frame_rate=%0.3f\n", 
                           coded_frame_rate, est_frame_rate);
#endif
                    /* if we detect that it could be a telecine, we
                       signal it. It would be better to do it at a
                       higher level as it can change in a film */
                    if (coded_frame_rate >= 24.97 && 
                        (est_frame_rate >= 23.5 && est_frame_rate < 24.5)) {
                        st->r_frame_rate = 24024;
                        st->r_frame_rate_base = 1001;
                    }
                }
            }
            /* if no real frame rate, use the codec one */
            if (!st->r_frame_rate){
                st->r_frame_rate      = st->codec.frame_rate;
                st->r_frame_rate_base = st->codec.frame_rate_base;
            }
        }
    }

    av_estimate_timings(ic);
    return ret;
}

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

/**
 * start playing a network based stream (e.g. RTSP stream) at the
 * current position 
 */
int av_read_play(AVFormatContext *s)
{
    if (!s->iformat->read_play)
        return AVERROR_NOTSUPP;
    return s->iformat->read_play(s);
}

/**
 * pause a network based stream (e.g. RTSP stream). Use av_read_play()
 * to resume it.
 */
int av_read_pause(AVFormatContext *s)
{
    if (!s->iformat->read_pause)
        return AVERROR_NOTSUPP;
    return s->iformat->read_pause(s);
}

/**
 * Close a media file (but not its codecs)
 *
 * @param s media file handle
 */
void av_close_input_file(AVFormatContext *s)
{
    int i, must_open_file;
    AVStream *st;

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

    if (s->iformat->read_close)
        s->iformat->read_close(s);
    for(i=0;i<s->nb_streams;i++) {
        /* free all data in a stream component */
        st = s->streams[i];
        if (st->parser) {
            av_parser_close(st->parser);
        }
        av_free(st->index_entries);
        av_free(st);
    }
    flush_packet_queue(s);
    must_open_file = 1;
    if (s->iformat->flags & AVFMT_NOFILE) {
        must_open_file = 0;
    }
    if (must_open_file) {
        url_fclose(&s->pb);
    }
    av_freep(&s->priv_data);
    av_free(s);
}

/**
 * Add a new stream to a media file. Can only be called in the
 * read_header function. If the flag AVFMTCTX_NOHEADER is in the
 * format context, then new streams can be added in read_packet too.
 *
 *
 * @param s media file handle
 * @param id file format dependent stream id 
 */
AVStream *av_new_stream(AVFormatContext *s, int id)
{
    AVStream *st;

    if (s->nb_streams >= MAX_STREAMS)
        return NULL;

    st = av_mallocz(sizeof(AVStream));
    if (!st)
        return NULL;
    avcodec_get_context_defaults(&st->codec);
    if (s->iformat) {
        /* no default bitrate if decoding */
        st->codec.bit_rate = 0;
    }
    st->index = s->nb_streams;
    st->id = id;
    st->start_time = AV_NOPTS_VALUE;
    st->duration = AV_NOPTS_VALUE;

    /* default pts settings is MPEG like */
    av_set_pts_info(st, 33, 1, 90000);
    st->last_pkt_pts = AV_NOPTS_VALUE;
    st->last_pkt_dts = AV_NOPTS_VALUE;
    st->last_pkt_stream_pts = AV_NOPTS_VALUE;
    st->last_pkt_stream_dts = AV_NOPTS_VALUE;

    s->streams[s->nb_streams++] = st;
    return st;
}

/************************************************************/
/* output media file */

int av_set_parameters(AVFormatContext *s, AVFormatParameters *ap)
{
    int ret;
    
    if (s->oformat->priv_data_size > 0) {
        s->priv_data = av_mallocz(s->oformat->priv_data_size);
        if (!s->priv_data)
            return AVERROR_NOMEM;
    } else
        s->priv_data = NULL;
	
    if (s->oformat->set_parameters) {
        ret = s->oformat->set_parameters(s, ap);
        if (ret < 0)
            return ret;
    }
    return 0;
}

/**
 * allocate the stream private data and write the stream header to an
 * output media file
 *
 * @param s media file handle
 * @return 0 if OK. AVERROR_xxx if error.  
 */
int av_write_header(AVFormatContext *s)
{
    int ret, i;
    AVStream *st;

    ret = s->oformat->write_header(s);
    if (ret < 0)
        return ret;

    /* init PTS generation */
    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];

        switch (st->codec.codec_type) {
        case CODEC_TYPE_AUDIO:
            av_frac_init(&st->pts, 0, 0, 
                         (int64_t)st->time_base.num * st->codec.sample_rate);
            break;
        case CODEC_TYPE_VIDEO:
            av_frac_init(&st->pts, 0, 0, 
                         (int64_t)st->time_base.num * st->codec.frame_rate);
            break;
        default:
            break;
        }
    }
    return 0;
}

/**
 * Write a packet to an output media file. The packet shall contain
 * one audio or video frame.
 *
 * @param s media file handle
 * @param stream_index stream index
 * @param buf buffer containing the frame data
 * @param size size of buffer
 * @return < 0 if error, = 0 if OK, 1 if end of stream wanted.
 */
int av_write_frame(AVFormatContext *s, int stream_index, const uint8_t *buf, 
                   int size)
{
    AVStream *st;
    int64_t pts_mask;
    int ret, frame_size;

    st = s->streams[stream_index];
    pts_mask = (1LL << st->pts_wrap_bits) - 1;

    /* HACK/FIXME we skip all zero size audio packets so a encoder can pass pts by outputing zero size packets */
    if(st->codec.codec_type==CODEC_TYPE_AUDIO && size==0)
        ret = 0;
    else
        ret = s->oformat->write_packet(s, stream_index, buf, size, 
                                       st->pts.val & pts_mask);
    
    if (ret < 0)
        return ret;

    /* update pts */
    switch (st->codec.codec_type) {
    case CODEC_TYPE_AUDIO:
        frame_size = get_audio_frame_size(&st->codec, size);

        /* HACK/FIXME, we skip the initial 0-size packets as they are most likely equal to the encoder delay,
           but it would be better if we had the real timestamps from the encoder */
        if (frame_size >= 0 && (size || st->pts.num!=st->pts.den>>1 || st->pts.val)) {
            av_frac_add(&st->pts, (int64_t)st->time_base.den * frame_size);
        }
        break;
    case CODEC_TYPE_VIDEO:
        av_frac_add(&st->pts, (int64_t)st->time_base.den * st->codec.frame_rate_base);
        break;
    default:
        break;
    }
    return ret;
}

/**
 * write the stream trailer to an output media file and and free the
 * file private data.
 *
 * @param s media file handle
 * @return 0 if OK. AVERROR_xxx if error.  */
int av_write_trailer(AVFormatContext *s)
{
    int ret;
    ret = s->oformat->write_trailer(s);
    av_freep(&s->priv_data);
    return ret;
}

/* "user interface" functions */

void dump_format(AVFormatContext *ic,
                 int index, 
                 const char *url,
                 int is_output)
{
    int i, flags;
    char buf[256];

    av_log(NULL, AV_LOG_DEBUG, "%s #%d, %s, %s '%s':\n", 
            is_output ? "Output" : "Input",
            index, 
            is_output ? ic->oformat->name : ic->iformat->name, 
            is_output ? "to" : "from", url);
    if (!is_output) {
        av_log(NULL, AV_LOG_DEBUG, "  Duration: ");
        if (ic->duration != AV_NOPTS_VALUE) {
            int hours, mins, secs, us;
            secs = ic->duration / AV_TIME_BASE;
            us = ic->duration % AV_TIME_BASE;
            mins = secs / 60;
            secs %= 60;
            hours = mins / 60;
            mins %= 60;
            av_log(NULL, AV_LOG_DEBUG, "%02d:%02d:%02d.%01d", hours, mins, secs, 
                   (10 * us) / AV_TIME_BASE);
        } else {
            av_log(NULL, AV_LOG_DEBUG, "N/A");
        }
        av_log(NULL, AV_LOG_DEBUG, ", bitrate: ");
        if (ic->bit_rate) {
            av_log(NULL, AV_LOG_DEBUG,"%d kb/s", ic->bit_rate / 1000);
        } else {
            av_log(NULL, AV_LOG_DEBUG, "N/A");
        }
        av_log(NULL, AV_LOG_DEBUG, "\n");
    }
    for(i=0;i<ic->nb_streams;i++) {
        AVStream *st = ic->streams[i];
        avcodec_string(buf, sizeof(buf), &st->codec, is_output);
        av_log(NULL, AV_LOG_DEBUG, "  Stream #%d.%d", index, i);
        /* the pid is an important information, so we display it */
        /* XXX: add a generic system */
        if (is_output)
            flags = ic->oformat->flags;
        else
            flags = ic->iformat->flags;
        if (flags & AVFMT_SHOW_IDS) {
            av_log(NULL, AV_LOG_DEBUG, "[0x%x]", st->id);
        }
        av_log(NULL, AV_LOG_DEBUG, ": %s\n", buf);
    }
}

typedef struct {
    const char *abv;
    int width, height;
    int frame_rate, frame_rate_base;
} AbvEntry;

static AbvEntry frame_abvs[] = {
    { "ntsc",      720, 480, 30000, 1001 },