utils.c

    if (ic->iformat->flags & AVFMT_NOFILE) {
        file_size = 0;
    } else {
        file_size = avio_size(ic->pb);
        file_size = FFMAX(0, file_size);
    }

    if ((!strcmp(ic->iformat->name, "mpeg") ||
         !strcmp(ic->iformat->name, "mpegts")) &&
        file_size && ic->pb->seekable) {
        /* get accurate estimate from the PTSes */
        estimate_timings_from_pts(ic, old_offset);
    } else if (has_duration(ic)) {
        /* at least one component has timings - we use them for all
           the components */
        fill_all_stream_timings(ic);
    } else {
        av_log(ic, AV_LOG_WARNING, "Estimating duration from bitrate, this may be inaccurate\n");
        /* less precise: use bitrate info */
        estimate_timings_from_bit_rate(ic);
    }
    update_stream_timings(ic);

    {
        int i;
        AVStream av_unused *st;
        for(i = 0;i < ic->nb_streams; i++) {
            st = ic->streams[i];
            av_dlog(ic, "%d: start_time: %0.3f duration: %0.3f\n", i,
                    (double) st->start_time / AV_TIME_BASE,
                    (double) st->duration   / AV_TIME_BASE);
        }
        av_dlog(ic, "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);
    }
}

static int has_codec_parameters(AVStream *st)
{
    AVCodecContext *avctx = st->codec;
    int val;
    switch (avctx->codec_type) {
    case AVMEDIA_TYPE_AUDIO:
        val = avctx->sample_rate && avctx->channels;
        if (st->info->found_decoder >= 0 && avctx->sample_fmt == AV_SAMPLE_FMT_NONE)
            return 0;
        break;
    case AVMEDIA_TYPE_VIDEO:
        val = avctx->width;
        if (st->info->found_decoder >= 0 && avctx->pix_fmt == PIX_FMT_NONE)
            return 0;
        break;
    default:
        val = 1;
        break;
    }
    return avctx->codec_id != CODEC_ID_NONE && val != 0;
}

static int has_decode_delay_been_guessed(AVStream *st)
{
    return st->codec->codec_id != CODEC_ID_H264 ||
        st->info->nb_decoded_frames >= 6;
}

/* returns 1 or 0 if or if not decoded data was returned, or a negative error */
static int try_decode_frame(AVStream *st, AVPacket *avpkt, AVDictionary **options)
{
    AVCodec *codec;
    int got_picture = 1, ret = 0;
    AVFrame picture;
    AVPacket pkt = *avpkt;

    if (!avcodec_is_open(st->codec) && !st->info->found_decoder) {
        AVDictionary *thread_opt = NULL;

        codec = st->codec->codec ? st->codec->codec :
                                   avcodec_find_decoder(st->codec->codec_id);

        if (!codec) {
            st->info->found_decoder = -1;
            return -1;
        }

        /* force thread count to 1 since the h264 decoder will not extract SPS
         *  and PPS to extradata during multi-threaded decoding */
        av_dict_set(options ? options : &thread_opt, "threads", "1", 0);
        ret = avcodec_open2(st->codec, codec, options ? options : &thread_opt);
        if (!options)
            av_dict_free(&thread_opt);
        if (ret < 0) {
            st->info->found_decoder = -1;
            return ret;
        }
        st->info->found_decoder = 1;
    } else if (!st->info->found_decoder)
        st->info->found_decoder = 1;

    if (st->info->found_decoder < 0)
        return -1;

    while ((pkt.size > 0 || (!pkt.data && got_picture)) &&
           ret >= 0 &&
           (!has_codec_parameters(st)         ||
           !has_decode_delay_been_guessed(st) ||
           (!st->codec_info_nb_frames && st->codec->codec->capabilities & CODEC_CAP_CHANNEL_CONF))) {
        got_picture = 0;
        avcodec_get_frame_defaults(&picture);
        switch(st->codec->codec_type) {
        case AVMEDIA_TYPE_VIDEO:
            ret = avcodec_decode_video2(st->codec, &picture,
                                        &got_picture, &pkt);
            break;
        case AVMEDIA_TYPE_AUDIO:
            ret = avcodec_decode_audio4(st->codec, &picture, &got_picture, &pkt);
            break;
        default:
            break;
        }
        if (ret >= 0) {
            if (got_picture)
                st->info->nb_decoded_frames++;
            pkt.data += ret;
            pkt.size -= ret;
            ret       = got_picture;
        }
    }
    return ret;
}

unsigned int ff_codec_get_tag(const AVCodecTag *tags, enum CodecID id)
{
    while (tags->id != CODEC_ID_NONE) {
        if (tags->id == id)
            return tags->tag;
        tags++;
    }
    return 0;
}

enum CodecID ff_codec_get_id(const AVCodecTag *tags, unsigned int tag)
{
    int i;
    for(i=0; tags[i].id != CODEC_ID_NONE;i++) {
        if(tag == tags[i].tag)
            return tags[i].id;
    }
    for(i=0; tags[i].id != CODEC_ID_NONE; i++) {
        if (avpriv_toupper4(tag) == avpriv_toupper4(tags[i].tag))
            return tags[i].id;
    }
    return CODEC_ID_NONE;
}

unsigned int av_codec_get_tag(const AVCodecTag * const *tags, enum CodecID id)
{
    int i;
    for(i=0; tags && tags[i]; i++){
        int tag= ff_codec_get_tag(tags[i], id);
        if(tag) return tag;
    }
    return 0;
}

enum CodecID av_codec_get_id(const AVCodecTag * const *tags, unsigned int tag)
{
    int i;
    for(i=0; tags && tags[i]; i++){
        enum CodecID id= ff_codec_get_id(tags[i], tag);
        if(id!=CODEC_ID_NONE) return id;
    }
    return CODEC_ID_NONE;
}

static void compute_chapters_end(AVFormatContext *s)
{
    unsigned int i, j;
    int64_t max_time = s->duration + ((s->start_time == AV_NOPTS_VALUE) ? 0 : s->start_time);

    for (i = 0; i < s->nb_chapters; i++)
        if (s->chapters[i]->end == AV_NOPTS_VALUE) {
            AVChapter *ch = s->chapters[i];
            int64_t   end = max_time ? av_rescale_q(max_time, AV_TIME_BASE_Q, ch->time_base)
                                     : INT64_MAX;

            for (j = 0; j < s->nb_chapters; j++) {
                AVChapter *ch1 = s->chapters[j];
                int64_t next_start = av_rescale_q(ch1->start, ch1->time_base, ch->time_base);
                if (j != i && next_start > ch->start && next_start < end)
                    end = next_start;
            }
            ch->end = (end == INT64_MAX) ? ch->start : end;
        }
}

static int get_std_framerate(int i){
    if(i<60*12) return i*1001;
    else        return ((const int[]){24,30,60,12,15})[i-60*12]*1000*12;
}

/*
 * Is the time base unreliable.
 * This is a heuristic to balance between quick acceptance of the values in
 * the headers vs. some extra checks.
 * Old DivX and Xvid often have nonsense timebases like 1fps or 2fps.
 * MPEG-2 commonly misuses field repeat flags to store different framerates.
 * And there are "variable" fps files this needs to detect as well.
 */
static int tb_unreliable(AVCodecContext *c){
    if(   c->time_base.den >= 101L*c->time_base.num
       || c->time_base.den <    5L*c->time_base.num
/*       || c->codec_tag == AV_RL32("DIVX")
       || c->codec_tag == AV_RL32("XVID")*/
       || c->codec_id == CODEC_ID_MPEG2VIDEO
       || c->codec_id == CODEC_ID_H264
       )
        return 1;
    return 0;
}

int avformat_find_stream_info(AVFormatContext *ic, AVDictionary **options)
{
    int i, count, ret, read_size, j;
    AVStream *st;
    AVPacket pkt1, *pkt;
    int64_t old_offset = avio_tell(ic->pb);
    int orig_nb_streams = ic->nb_streams;        // new streams might appear, no options for those

    for(i=0;i<ic->nb_streams;i++) {
        AVCodec *codec;
        AVDictionary *thread_opt = NULL;
        st = ic->streams[i];

        //only for the split stuff
        if (!st->parser && !(ic->flags & AVFMT_FLAG_NOPARSE)) {
            st->parser = av_parser_init(st->codec->codec_id);
            if(st->need_parsing == AVSTREAM_PARSE_HEADERS && st->parser){
                st->parser->flags |= PARSER_FLAG_COMPLETE_FRAMES;
            }
        }
        codec = st->codec->codec ? st->codec->codec :
                                   avcodec_find_decoder(st->codec->codec_id);

        /* force thread count to 1 since the h264 decoder will not extract SPS
         *  and PPS to extradata during multi-threaded decoding */
        av_dict_set(options ? &options[i] : &thread_opt, "threads", "1", 0);

        /* Ensure that subtitle_header is properly set. */
        if (st->codec->codec_type == AVMEDIA_TYPE_SUBTITLE
            && codec && !st->codec->codec)
            avcodec_open2(st->codec, codec, options ? &options[i]
                              : &thread_opt);

        //try to just open decoders, in case this is enough to get parameters
        if (!has_codec_parameters(st)) {
            if (codec && !st->codec->codec)
                avcodec_open2(st->codec, codec, options ? &options[i]
                              : &thread_opt);
        }
        if (!options)
            av_dict_free(&thread_opt);
    }

    for (i=0; i<ic->nb_streams; i++) {
        ic->streams[i]->info->last_dts = AV_NOPTS_VALUE;
    }

    count = 0;
    read_size = 0;
    for(;;) {
        if (ff_check_interrupt(&ic->interrupt_callback)){
            ret= AVERROR_EXIT;
            av_log(ic, AV_LOG_DEBUG, "interrupted\n");
            break;
        }

        /* check if one codec still needs to be handled */
        for(i=0;i<ic->nb_streams;i++) {
            int fps_analyze_framecount = 20;

            st = ic->streams[i];
            if (!has_codec_parameters(st))
                break;
            /* if the timebase is coarse (like the usual millisecond precision
               of mkv), we need to analyze more frames to reliably arrive at
               the correct fps */
            if (av_q2d(st->time_base) > 0.0005)
                fps_analyze_framecount *= 2;
            if (ic->fps_probe_size >= 0)
                fps_analyze_framecount = ic->fps_probe_size;
            /* variable fps and no guess at the real fps */
            if(   tb_unreliable(st->codec) && !(st->r_frame_rate.num && st->avg_frame_rate.num)
               && st->info->duration_count < fps_analyze_framecount
               && st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
                break;
            if(st->parser && st->parser->parser->split && !st->codec->extradata)
                break;
            if(st->first_dts == AV_NOPTS_VALUE)
                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;
                av_log(ic, AV_LOG_DEBUG, "All info found\n");
                break;
            }
        }
        /* we did not get all the codec info, but we read too much data */
        if (read_size >= ic->probesize) {
            ret = count;
            av_log(ic, AV_LOG_DEBUG, "Probe buffer size limit %d reached\n", ic->probesize);
            break;
        }

        /* NOTE: a new stream can be added there if no header in file
           (AVFMTCTX_NOHEADER) */
        ret = read_frame_internal(ic, &pkt1);
        if (ret == AVERROR(EAGAIN))
            continue;

        if (ret < 0) {
            /* EOF or error*/
            AVPacket empty_pkt = { 0 };
            int err = 0;
            av_init_packet(&empty_pkt);

            ret = -1; /* we could not have all the codec parameters before EOF */
            for(i=0;i<ic->nb_streams;i++) {
                st = ic->streams[i];

                /* flush the decoders */
                if (st->info->found_decoder == 1) {
                    do {
                        err = try_decode_frame(st, &empty_pkt,
                                               (options && i < orig_nb_streams) ?
                                               &options[i] : NULL);
                    } while (err > 0 && !has_codec_parameters(st));
                }

                if (err < 0) {
                    av_log(ic, AV_LOG_WARNING,
                           "decoding for stream %d failed\n", st->index);
                } else if (!has_codec_parameters(st)) {
                    char buf[256];
                    avcodec_string(buf, sizeof(buf), st->codec, 0);
                    av_log(ic, AV_LOG_WARNING,
                           "Could not find codec parameters (%s)\n", buf);
                } else {
                    ret = 0;
                }
            }
            break;
        }

        pkt= add_to_pktbuf(&ic->packet_buffer, &pkt1, &ic->packet_buffer_end);
        if ((ret = av_dup_packet(pkt)) < 0)
            goto find_stream_info_err;

        read_size += pkt->size;

        st = ic->streams[pkt->stream_index];
        if (st->codec_info_nb_frames>1) {
            if (av_rescale_q(st->info->codec_info_duration, st->time_base, AV_TIME_BASE_Q) >= ic->max_analyze_duration) {
                av_log(ic, AV_LOG_WARNING, "max_analyze_duration reached\n");
                break;
            }
            st->info->codec_info_duration += pkt->duration;
        }
        {
            int64_t last = st->info->last_dts;

            if(pkt->dts != AV_NOPTS_VALUE && last != AV_NOPTS_VALUE && pkt->dts > last){
                int64_t duration= pkt->dts - last;
                double dur= duration * av_q2d(st->time_base);

//                if(st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
//                    av_log(NULL, AV_LOG_ERROR, "%f\n", dur);
                if (st->info->duration_count < 2)
                    memset(st->info->duration_error, 0, sizeof(st->info->duration_error));
                for (i=1; i<FF_ARRAY_ELEMS(st->info->duration_error); i++) {
                    int framerate= get_std_framerate(i);
                    int ticks= lrintf(dur*framerate/(1001*12));
                    double error = dur - (double)ticks*1001*12 / framerate;
                    st->info->duration_error[i] += error*error;
                }
                st->info->duration_count++;
                // ignore the first 4 values, they might have some random jitter
                if (st->info->duration_count > 3)
                    st->info->duration_gcd = av_gcd(st->info->duration_gcd, duration);
            }
            if (last == AV_NOPTS_VALUE || st->info->duration_count <= 1)
                st->info->last_dts = pkt->dts;
        }
        if(st->parser && st->parser->parser->split && !st->codec->extradata){
            int i= st->parser->parser->split(st->codec, pkt->data, pkt->size);
            if (i > 0 && i < FF_MAX_EXTRADATA_SIZE) {
                st->codec->extradata_size= i;
                st->codec->extradata= av_malloc(st->codec->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
                if (!st->codec->extradata)
                    return AVERROR(ENOMEM);
                memcpy(st->codec->extradata, pkt->data, st->codec->extradata_size);
                memset(st->codec->extradata + i, 0, FF_INPUT_BUFFER_PADDING_SIZE);
            }
        }

        /* 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 MPEG-4, we need to
           decompress for QuickTime.

           If CODEC_CAP_CHANNEL_CONF is set this will force decoding of at
           least one frame of codec data, this makes sure the codec initializes
           the channel configuration and does not only trust the values from the container.
        */
        try_decode_frame(st, pkt, (options && i < orig_nb_streams ) ? &options[i] : NULL);

        st->codec_info_nb_frames++;
        count++;
    }

    // close codecs which were opened in try_decode_frame()
    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        avcodec_close(st->codec);
    }
    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
            if (st->codec_info_nb_frames>2 && !st->avg_frame_rate.num && st->info->codec_info_duration)
                av_reduce(&st->avg_frame_rate.num, &st->avg_frame_rate.den,
                          (st->codec_info_nb_frames-2)*(int64_t)st->time_base.den,
                          st->info->codec_info_duration*(int64_t)st->time_base.num, 60000);
            // the check for tb_unreliable() is not completely correct, since this is not about handling
            // a unreliable/inexact time base, but a time base that is finer than necessary, as e.g.
            // ipmovie.c produces.
            if (tb_unreliable(st->codec) && st->info->duration_count > 15 && st->info->duration_gcd > 1 && !st->r_frame_rate.num)
                av_reduce(&st->r_frame_rate.num, &st->r_frame_rate.den, st->time_base.den, st->time_base.num * st->info->duration_gcd, INT_MAX);
            if (st->info->duration_count && !st->r_frame_rate.num
               && tb_unreliable(st->codec) /*&&
               //FIXME we should not special-case MPEG-2, but this needs testing with non-MPEG-2 ...
               st->time_base.num*duration_sum[i]/st->info->duration_count*101LL > st->time_base.den*/){
                int num = 0;
                double best_error= 2*av_q2d(st->time_base);
                best_error = best_error*best_error*st->info->duration_count*1000*12*30;

                for (j=1; j<FF_ARRAY_ELEMS(st->info->duration_error); j++) {
                    double error = st->info->duration_error[j] * get_std_framerate(j);
//                    if(st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
//                        av_log(NULL, AV_LOG_ERROR, "%f %f\n", get_std_framerate(j) / 12.0/1001, error);
                    if(error < best_error){
                        best_error= error;
                        num = get_std_framerate(j);
                    }
                }
                // do not increase frame rate by more than 1 % in order to match a standard rate.
                if (num && (!st->r_frame_rate.num || (double)num/(12*1001) < 1.01 * av_q2d(st->r_frame_rate)))
                    av_reduce(&st->r_frame_rate.num, &st->r_frame_rate.den, num, 12*1001, INT_MAX);
            }
        }else if(st->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
            if(!st->codec->bits_per_coded_sample)
                st->codec->bits_per_coded_sample= av_get_bits_per_sample(st->codec->codec_id);
            // set stream disposition based on audio service type
            switch (st->codec->audio_service_type) {
            case AV_AUDIO_SERVICE_TYPE_EFFECTS:
                st->disposition = AV_DISPOSITION_CLEAN_EFFECTS;    break;
            case AV_AUDIO_SERVICE_TYPE_VISUALLY_IMPAIRED:
                st->disposition = AV_DISPOSITION_VISUAL_IMPAIRED;  break;
            case AV_AUDIO_SERVICE_TYPE_HEARING_IMPAIRED:
                st->disposition = AV_DISPOSITION_HEARING_IMPAIRED; break;
            case AV_AUDIO_SERVICE_TYPE_COMMENTARY:
                st->disposition = AV_DISPOSITION_COMMENT;          break;
            case AV_AUDIO_SERVICE_TYPE_KARAOKE:
                st->disposition = AV_DISPOSITION_KARAOKE;          break;
            }
        }
    }

    estimate_timings(ic, old_offset);

    compute_chapters_end(ic);

 find_stream_info_err:
    for (i=0; i < ic->nb_streams; i++) {
        if (ic->streams[i]->codec)
            ic->streams[i]->codec->thread_count = 0;
        av_freep(&ic->streams[i]->info);
    }
    return ret;
}

static AVProgram *find_program_from_stream(AVFormatContext *ic, int s)
{
    int i, j;

    for (i = 0; i < ic->nb_programs; i++)
        for (j = 0; j < ic->programs[i]->nb_stream_indexes; j++)
            if (ic->programs[i]->stream_index[j] == s)
                return ic->programs[i];
    return NULL;
}

int av_find_best_stream(AVFormatContext *ic,
                        enum AVMediaType type,
                        int wanted_stream_nb,
                        int related_stream,
                        AVCodec **decoder_ret,
                        int flags)
{
    int i, nb_streams = ic->nb_streams;
    int ret = AVERROR_STREAM_NOT_FOUND, best_count = -1;
    unsigned *program = NULL;
    AVCodec *decoder = NULL, *best_decoder = NULL;

    if (related_stream >= 0 && wanted_stream_nb < 0) {
        AVProgram *p = find_program_from_stream(ic, related_stream);
        if (p) {
            program = p->stream_index;
            nb_streams = p->nb_stream_indexes;
        }
    }
    for (i = 0; i < nb_streams; i++) {
        int real_stream_index = program ? program[i] : i;
        AVStream *st = ic->streams[real_stream_index];
        AVCodecContext *avctx = st->codec;
        if (avctx->codec_type != type)
            continue;
        if (wanted_stream_nb >= 0 && real_stream_index != wanted_stream_nb)
            continue;
        if (st->disposition & (AV_DISPOSITION_HEARING_IMPAIRED|AV_DISPOSITION_VISUAL_IMPAIRED))
            continue;
        if (decoder_ret) {
            decoder = avcodec_find_decoder(st->codec->codec_id);
            if (!decoder) {
                if (ret < 0)
                    ret = AVERROR_DECODER_NOT_FOUND;
                continue;
            }
        }
        if (best_count >= st->codec_info_nb_frames)
            continue;
        best_count = st->codec_info_nb_frames;
        ret = real_stream_index;
        best_decoder = decoder;
        if (program && i == nb_streams - 1 && ret < 0) {
            program = NULL;
            nb_streams = ic->nb_streams;
            i = 0; /* no related stream found, try again with everything */
        }
    }
    if (decoder_ret)
        *decoder_ret = best_decoder;
    return ret;
}

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

int av_read_play(AVFormatContext *s)
{
    if (s->iformat->read_play)
        return s->iformat->read_play(s);
    if (s->pb)
        return avio_pause(s->pb, 0);
    return AVERROR(ENOSYS);
}

int av_read_pause(AVFormatContext *s)
{
    if (s->iformat->read_pause)
        return s->iformat->read_pause(s);
    if (s->pb)
        return avio_pause(s->pb, 1);
    return AVERROR(ENOSYS);
}

void avformat_free_context(AVFormatContext *s)
{
    int i;
    AVStream *st;

    av_opt_free(s);
    if (s->iformat && s->iformat->priv_class && s->priv_data)
        av_opt_free(s->priv_data);

    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);
        }
        if (st->attached_pic.data)
            av_free_packet(&st->attached_pic);
        av_dict_free(&st->metadata);
        av_free(st->index_entries);
        av_free(st->codec->extradata);
        av_free(st->codec->subtitle_header);
        av_free(st->codec);
        av_free(st->priv_data);
        av_free(st->info);
        av_free(st);
    }
    for(i=s->nb_programs-1; i>=0; i--) {
        av_dict_free(&s->programs[i]->metadata);
        av_freep(&s->programs[i]->stream_index);
        av_freep(&s->programs[i]);
    }
    av_freep(&s->programs);
    av_freep(&s->priv_data);
    while(s->nb_chapters--) {
        av_dict_free(&s->chapters[s->nb_chapters]->metadata);
        av_free(s->chapters[s->nb_chapters]);
    }
    av_freep(&s->chapters);
    av_dict_free(&s->metadata);
    av_freep(&s->streams);
    av_free(s);
}

#if FF_API_CLOSE_INPUT_FILE
void av_close_input_file(AVFormatContext *s)
{
    avformat_close_input(&s);
}
#endif

void avformat_close_input(AVFormatContext **ps)
{
    AVFormatContext *s = *ps;
    AVIOContext *pb = (s->iformat->flags & AVFMT_NOFILE) || (s->flags & AVFMT_FLAG_CUSTOM_IO) ?
                       NULL : s->pb;
    flush_packet_queue(s);
    if (s->iformat->read_close)
        s->iformat->read_close(s);
    avformat_free_context(s);
    *ps = NULL;
    if (pb)
        avio_close(pb);
}

AVStream *avformat_new_stream(AVFormatContext *s, AVCodec *c)
{
    AVStream *st;
    int i;
    AVStream **streams;

    if (s->nb_streams >= INT_MAX/sizeof(*streams))
        return NULL;
    streams = av_realloc(s->streams, (s->nb_streams + 1) * sizeof(*streams));
    if (!streams)
        return NULL;
    s->streams = streams;

    st = av_mallocz(sizeof(AVStream));
    if (!st)
        return NULL;
    if (!(st->info = av_mallocz(sizeof(*st->info)))) {
        av_free(st);
        return NULL;
    }

    st->codec = avcodec_alloc_context3(c);
    if (s->iformat) {
        /* no default bitrate if decoding */
        st->codec->bit_rate = 0;
    }
    st->index = s->nb_streams;
    st->start_time = AV_NOPTS_VALUE;
    st->duration = AV_NOPTS_VALUE;
        /* we set the current DTS to 0 so that formats without any timestamps
           but durations get some timestamps, formats with some unknown
           timestamps have their first few packets buffered and the
           timestamps corrected before they are returned to the user */
    st->cur_dts = 0;
    st->first_dts = AV_NOPTS_VALUE;
    st->probe_packets = MAX_PROBE_PACKETS;

    /* default pts setting is MPEG-like */
    avpriv_set_pts_info(st, 33, 1, 90000);
    st->last_IP_pts = AV_NOPTS_VALUE;
    for(i=0; i<MAX_REORDER_DELAY+1; i++)
        st->pts_buffer[i]= AV_NOPTS_VALUE;
    st->reference_dts = AV_NOPTS_VALUE;

    st->sample_aspect_ratio = (AVRational){0,1};

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

AVProgram *av_new_program(AVFormatContext *ac, int id)
{
    AVProgram *program=NULL;
    int i;

    av_dlog(ac, "new_program: id=0x%04x\n", id);

    for(i=0; i<ac->nb_programs; i++)
        if(ac->programs[i]->id == id)
            program = ac->programs[i];

    if(!program){
        program = av_mallocz(sizeof(AVProgram));
        if (!program)
            return NULL;
        dynarray_add(&ac->programs, &ac->nb_programs, program);
        program->discard = AVDISCARD_NONE;
    }
    program->id = id;

    return program;
}

AVChapter *avpriv_new_chapter(AVFormatContext *s, int id, AVRational time_base, int64_t start, int64_t end, const char *title)
{
    AVChapter *chapter = NULL;
    int i;

    for(i=0; i<s->nb_chapters; i++)
        if(s->chapters[i]->id == id)
            chapter = s->chapters[i];

    if(!chapter){
        chapter= av_mallocz(sizeof(AVChapter));
        if(!chapter)
            return NULL;
        dynarray_add(&s->chapters, &s->nb_chapters, chapter);
    }
    av_dict_set(&chapter->metadata, "title", title, 0);
    chapter->id    = id;
    chapter->time_base= time_base;
    chapter->start = start;
    chapter->end   = end;

    return chapter;
}

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

static int validate_codec_tag(AVFormatContext *s, AVStream *st)
{
    const AVCodecTag *avctag;
    int n;
    enum CodecID id = CODEC_ID_NONE;
    unsigned int tag = 0;

    /**
     * Check that tag + id is in the table
     * If neither is in the table -> OK
     * If tag is in the table with another id -> FAIL
     * If id is in the table with another tag -> FAIL unless strict < normal
     */
    for (n = 0; s->oformat->codec_tag[n]; n++) {
        avctag = s->oformat->codec_tag[n];
        while (avctag->id != CODEC_ID_NONE) {
            if (avpriv_toupper4(avctag->tag) == avpriv_toupper4(st->codec->codec_tag)) {
                id = avctag->id;
                if (id == st->codec->codec_id)
                    return 1;
            }
            if (avctag->id == st->codec->codec_id)
                tag = avctag->tag;
            avctag++;
        }
    }
    if (id != CODEC_ID_NONE)
        return 0;
    if (tag && (st->codec->strict_std_compliance >= FF_COMPLIANCE_NORMAL))
        return 0;
    return 1;
}

int avformat_write_header(AVFormatContext *s, AVDictionary **options)
{
    int ret = 0, i;
    AVStream *st;
    AVDictionary *tmp = NULL;

    if (options)
        av_dict_copy(&tmp, *options, 0);
    if ((ret = av_opt_set_dict(s, &tmp)) < 0)
        goto fail;

    // some sanity checks
    if (s->nb_streams == 0 && !(s->oformat->flags & AVFMT_NOSTREAMS)) {
        av_log(s, AV_LOG_ERROR, "no streams\n");
        ret = AVERROR(EINVAL);
        goto fail;
    }

    for(i=0;i<s->nb_streams;i++) {
        st = s->streams[i];

        switch (st->codec->codec_type) {
        case AVMEDIA_TYPE_AUDIO:
            if(st->codec->sample_rate<=0){
                av_log(s, AV_LOG_ERROR, "sample rate not set\n");
                ret = AVERROR(EINVAL);
                goto fail;
            }
            if(!st->codec->block_align)
                st->codec->block_align = st->codec->channels *
                    av_get_bits_per_sample(st->codec->codec_id) >> 3;
            break;
        case AVMEDIA_TYPE_VIDEO:
            if(st->codec->time_base.num<=0 || st->codec->time_base.den<=0){ //FIXME audio too?
                av_log(s, AV_LOG_ERROR, "time base not set\n");
                ret = AVERROR(EINVAL);
                goto fail;
            }
            if((st->codec->width<=0 || st->codec->height<=0) && !(s->oformat->flags & AVFMT_NODIMENSIONS)){
                av_log(s, AV_LOG_ERROR, "dimensions not set\n");
                ret = AVERROR(EINVAL);
                goto fail;
            }
            if(av_cmp_q(st->sample_aspect_ratio, st->codec->sample_aspect_ratio)){
                av_log(s, AV_LOG_ERROR, "Aspect ratio mismatch between muxer "
                       "(%d/%d) and encoder layer (%d/%d)\n",
                       st->sample_aspect_ratio.num, st->sample_aspect_ratio.den,
                       st->codec->sample_aspect_ratio.num,
                       st->codec->sample_aspect_ratio.den);
                ret = AVERROR(EINVAL);
                goto fail;
            }
            break;
        }

        if(s->oformat->codec_tag){
            if(st->codec->codec_tag && st->codec->codec_id == CODEC_ID_RAWVIDEO && av_codec_get_tag(s->oformat->codec_tag, st->codec->codec_id) == 0 && !validate_codec_tag(s, st)){
                //the current rawvideo encoding system ends up setting the wrong codec_tag for avi, we override it here
                st->codec->codec_tag= 0;
            }
            if(st->codec->codec_tag){
                if (!validate_codec_tag(s, st)) {
                    char tagbuf[32];
                    av_get_codec_tag_string(tagbuf, sizeof(tagbuf), st->codec->codec_tag);
                    av_log(s, AV_LOG_ERROR,
                           "Tag %s/0x%08x incompatible with output codec id '%d'\n",
                           tagbuf, st->codec->codec_tag, st->codec->codec_id);
                    ret = AVERROR_INVALIDDATA;
                    goto fail;
                }
            }else
                st->codec->codec_tag= av_codec_get_tag(s->oformat->codec_tag, st->codec->codec_id);
        }

        if(s->oformat->flags & AVFMT_GLOBALHEADER &&
            !(st->codec->flags & CODEC_FLAG_GLOBAL_HEADER))
          av_log(s, AV_LOG_WARNING, "Codec for stream %d does not use global headers but container format requires global headers\n", i);
    }

    if (!s->priv_data && s->oformat->priv_data_size > 0) {
        s->priv_data = av_mallocz(s->oformat->priv_data_size);
        if (!s->priv_data) {
            ret = AVERROR(ENOMEM);
            goto fail;
        }
        if (s->oformat->priv_class) {
            *(const AVClass**)s->priv_data= s->oformat->priv_class;
            av_opt_set_defaults(s->priv_data);
            if ((ret = av_opt_set_dict(s->priv_data, &tmp)) < 0)
                goto fail;
        }
    }

    /* set muxer identification string */
    if (s->nb_streams && !(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {
        av_dict_set(&s->metadata, "encoder", LIBAVFORMAT_IDENT, 0);
    }

    if(s->oformat->write_header){
        ret = s->oformat->write_header(s);
        if (ret < 0)
            goto fail;
    }

    /* init PTS generation */
    for(i=0;i<s->nb_streams;i++) {
        int64_t den = AV_NOPTS_VALUE;
        st = s->streams[i];

        switch (st->codec->codec_type) {
        case AVMEDIA_TYPE_AUDIO:
            den = (int64_t)st->time_base.num * st->codec->sample_rate;
            break;
        case AVMEDIA_TYPE_VIDEO:
            den = (int64_t)st->time_base.num * st->codec->time_base.den;
            break;
        default:
            break;
        }
        if (den != AV_NOPTS_VALUE) {
            if (den <= 0) {
                ret = AVERROR_INVALIDDATA;
                goto fail;
            }
            frac_init(&st->pts, 0, 0, den);
        }
    }

    if (options) {
        av_dict_free(options);
        *options = tmp;
    }
    return 0;
fail:
    av_dict_free(&tmp);
    return ret;
}

//FIXME merge with compute_pkt_fields
static int compute_pkt_fields2(AVFormatContext *s, AVStream *st, AVPacket *pkt){
    int delay = FFMAX(st->codec->has_b_frames, !!st->codec->max_b_frames);
    int num, den, frame_size, i;

    av_dlog(s, "compute_pkt_fields2: pts:%"PRId64" dts:%"PRId64" cur_dts:%"PRId64" b:%d size:%d st:%d\n",
            pkt->pts, pkt->dts, st->cur_dts, delay, pkt->size, pkt->stream_index);

/*    if(pkt->pts == AV_NOPTS_VALUE && pkt->dts == AV_NOPTS_VALUE)
        return AVERROR(EINVAL);*/

    /* duration field */
    if (pkt->duration == 0) {
        compute_frame_duration(&num, &den, st, NULL, pkt);
        if (den && num) {
            pkt->duration = av_rescale(1, num * (int64_t)st->time_base.den * st->codec->ticks_per_frame, den * (int64_t)st->time_base.num);
        }
    }

    if(pkt->pts == AV_NOPTS_VALUE && pkt->dts != AV_NOPTS_VALUE && delay==0)
        pkt->pts= pkt->dts;

    //XXX/FIXME this is a temporary hack until all encoders output pts
    if((pkt->pts == 0 || pkt->pts == AV_NOPTS_VALUE) && pkt->dts == AV_NOPTS_VALUE && !delay){
        pkt->dts=
//        pkt->pts= st->cur_dts;
        pkt->pts= st->pts.val;
    }

    //calculate dts from pts
    if(pkt->pts != AV_NOPTS_VALUE && pkt->dts == AV_NOPTS_VALUE && delay <= MAX_REORDER_DELAY){
        st->pts_buffer[0]= pkt->pts;
        for(i=1; i<delay+1 && st->pts_buffer[i] == AV_NOPTS_VALUE; i++)
            st->pts_buffer[i]= pkt->pts + (i-delay-1) * pkt->duration;
        for(i=0; i<delay && st->pts_buffer[i] > st->pts_buffer[i+1]; i++)
            FFSWAP(int64_t, st->pts_buffer[i], st->pts_buffer[i+1]);

        pkt->dts= st->pts_buffer[0];
    }

    if(st->cur_dts && st->cur_dts != AV_NOPTS_VALUE && st->cur_dts >= pkt->dts){
        av_log(s, AV_LOG_ERROR,
               "Application provided invalid, non monotonically increasing dts to muxer in stream %d: %"PRId64" >= %"PRId64"\n",
               st->index, st->cur_dts, pkt->dts);
        return AVERROR(EINVAL);
    }
    if(pkt->dts != AV_NOPTS_VALUE && pkt->pts != AV_NOPTS_VALUE && pkt->pts < pkt->dts){
        av_log(s, AV_LOG_ERROR, "pts < dts in stream %d\n", st->index);
        return AVERROR(EINVAL);
    }

//    av_log(s, AV_LOG_DEBUG, "av_write_frame: pts2:%"PRId64" dts2:%"PRId64"\n", pkt->pts, pkt->dts);
    st->cur_dts= pkt->dts;
    st->pts.val= pkt->dts;

    /* update pts */
    switch (st->codec->codec_type) {
    case AVMEDIA_TYPE_AUDIO:
        frame_size = get_audio_frame_size(st->codec, pkt->size, 1);

        /* 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 && (pkt->size || st->pts.num!=st->pts.den>>1 || st->pts.val)) {
            frac_add(&st->pts, (int64_t)st->time_base.den * frame_size);
        }
        break;
    case AVMEDIA_TYPE_VIDEO:
        frac_add(&st->pts, (int64_t)st->time_base.den * st->codec->time_base.num);
        break;
    default:
        break;
    }
    return 0;
}

int av_write_frame(AVFormatContext *s, AVPacket *pkt)
{
    int ret;

    if (!pkt) {
        if (s->oformat->flags & AVFMT_ALLOW_FLUSH)
            return s->oformat->write_packet(s, pkt);
        return 1;
    }