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

    if ((!strcmp(ic->iformat->name, "mpeg") ||
         !strcmp(ic->iformat->name, "mpegts")) &&
        file_size && !ic->pb.is_streamed) {
        /* get accurate estimate from the PTSes */
        av_estimate_timings_from_pts(ic, old_offset);
    } else if (av_has_duration(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 && enc->pix_fmt != PIX_FMT_NONE;
        break;
    default:
        val = 1;
        break;
    }
    return (enc->codec_id != CODEC_ID_NONE && val != 0);
}

static int try_decode_frame(AVStream *st, const uint8_t *data, int size)
{
    int16_t *samples;
    AVCodec *codec;
    int got_picture, data_size, ret=0;
    AVFrame picture;

  if(!st->codec->codec){
    codec = avcodec_find_decoder(st->codec->codec_id);
    if (!codec)
        return -1;
    ret = avcodec_open(st->codec, codec);
    if (ret < 0)
        return ret;
  }

  if(!has_codec_parameters(st->codec)){
    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:
        data_size = FFMAX(size, AVCODEC_MAX_AUDIO_FRAME_SIZE);
        samples = av_malloc(data_size);
        if (!samples)
            goto fail;
        ret = avcodec_decode_audio2(st->codec, samples,
                                    &data_size, (uint8_t *)data, size);
        av_free(samples);
        break;
    default:
        break;
    }
  }
 fail:
    return ret;
}

static int set_codec_from_probe_data(AVStream *st, AVProbeData *pd, int score)
{
    AVInputFormat *fmt;
    fmt = av_probe_input_format2(pd, 1, &score);

    if (fmt) {
        if (strncmp(fmt->name, "mp3", 3) == 0)
            st->codec->codec_id = CODEC_ID_MP3;
        else if (strncmp(fmt->name, "ac3", 3) == 0)
            st->codec->codec_id = CODEC_ID_AC3;
    }
    return !!fmt;
}

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

enum CodecID 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(   toupper((tag >> 0)&0xFF) == toupper((tags[i].tag >> 0)&0xFF)
           && toupper((tag >> 8)&0xFF) == toupper((tags[i].tag >> 8)&0xFF)
           && toupper((tag >>16)&0xFF) == toupper((tags[i].tag >>16)&0xFF)
           && toupper((tag >>24)&0xFF) == toupper((tags[i].tag >>24)&0xFF))
            return tags[i].id;
    }
    return CODEC_ID_NONE;
}

unsigned int av_codec_get_tag(const AVCodecTag *tags[4], enum CodecID id)
{
    int i;
    for(i=0; tags && tags[i]; i++){
        int tag= codec_get_tag(tags[i], id);
        if(tag) return tag;
    }
    return 0;
}

enum CodecID av_codec_get_id(const AVCodecTag *tags[4], unsigned int tag)
{
    int i;
    for(i=0; tags && tags[i]; i++){
        enum CodecID id= codec_get_id(tags[i], tag);
        if(id!=CODEC_ID_NONE) return id;
    }
    return CODEC_ID_NONE;
}

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

#define MAX_STD_TIMEBASES (60*12+5)
static int get_std_framerate(int i){
    if(i<60*12) return i*1001;
    else        return ((int[]){24,30,60,12,15})[i-60*12]*1000*12;
}

int av_find_stream_info(AVFormatContext *ic)
{
    int i, count, ret, read_size, j;
    AVStream *st;
    AVPacket pkt1, *pkt;
    int64_t last_dts[MAX_STREAMS];
    int duration_count[MAX_STREAMS]={0};
    double (*duration_error)[MAX_STD_TIMEBASES];
    offset_t old_offset = url_ftell(&ic->pb);
    int64_t codec_info_duration[MAX_STREAMS]={0};
    int codec_info_nb_frames[MAX_STREAMS]={0};
    AVProbeData probe_data[MAX_STREAMS];
    int codec_identified[MAX_STREAMS]={0};

    duration_error = av_mallocz(MAX_STREAMS * sizeof(*duration_error));
    if (!duration_error) return AVERROR(ENOMEM);

    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if(st->codec->codec_type == CODEC_TYPE_VIDEO){
/*            if(!st->time_base.num)
                st->time_base= */
            if(!st->codec->time_base.num)
                st->codec->time_base= st->time_base;
        }
        //only for the split stuff
        if (!st->parser) {
            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;
            }
        }
    }

    for(i=0;i<MAX_STREAMS;i++){
        last_dts[i]= AV_NOPTS_VALUE;
    }

    memset(probe_data, 0, sizeof(probe_data));
    count = 0;
    read_size = 0;
    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;
            /* variable fps and no guess at the real fps */
            if(   (st->codec->time_base.den >= 101LL*st->codec->time_base.num || st->codec->codec_id == CODEC_ID_MPEG2VIDEO)
               && duration_count[i]<20 && st->codec->codec_type == CODEC_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;
                break;
            }
        }
        /* 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 */
            for(i=0;i<ic->nb_streams;i++) {
                st = ic->streams[i];
                if (!has_codec_parameters(st->codec)){
                    char buf[256];
                    avcodec_string(buf, sizeof(buf), st->codec, 0);
                    av_log(ic, AV_LOG_INFO, "Could not find codec parameters (%s)\n", buf);
                } else {
                    ret = 0;
                }
            }
            break;
        }

        pkt= add_to_pktbuf(ic, &pkt1);
        if(av_dup_packet(pkt) < 0)
            return AVERROR(ENOMEM);

        read_size += pkt->size;

        st = ic->streams[pkt->stream_index];
        if(codec_info_nb_frames[st->index]>1)
            codec_info_duration[st->index] += pkt->duration;
        if (pkt->duration != 0)
            codec_info_nb_frames[st->index]++;

        {
            int index= pkt->stream_index;
            int64_t last= last_dts[index];
            int64_t duration= pkt->dts - last;

            if(pkt->dts != AV_NOPTS_VALUE && last != AV_NOPTS_VALUE && duration>0){
                double dur= duration * av_q2d(st->time_base);

//                if(st->codec->codec_type == CODEC_TYPE_VIDEO)
//                    av_log(NULL, AV_LOG_ERROR, "%f\n", dur);
                if(duration_count[index] < 2)
                    memset(duration_error, 0, MAX_STREAMS * sizeof(*duration_error));
                for(i=1; i<MAX_STD_TIMEBASES; i++){
                    int framerate= get_std_framerate(i);
                    int ticks= lrintf(dur*framerate/(1001*12));
                    double error= dur - ticks*1001*12/(double)framerate;
                    duration_error[index][i] += error*error;
                }
                duration_count[index]++;
            }
            if(last == AV_NOPTS_VALUE || duration_count[index]<=1)
                last_dts[pkt->stream_index]= pkt->dts;

            if (st->codec->codec_id == CODEC_ID_NONE) {
                AVProbeData *pd = &(probe_data[st->index]);
                pd->buf = av_realloc(pd->buf, pd->buf_size+pkt->size+AVPROBE_PADDING_SIZE);
                memcpy(pd->buf+pd->buf_size, pkt->data, pkt->size);
                pd->buf_size += pkt->size;
                memset(pd->buf+pd->buf_size, 0, AVPROBE_PADDING_SIZE);
            }
        }
        if(st->parser && st->parser->parser->split && !st->codec->extradata){
            int i= st->parser->parser->split(st->codec, pkt->data, pkt->size);
            if(i){
                st->codec->extradata_size= i;
                st->codec->extradata= av_malloc(st->codec->extradata_size + FF_INPUT_BUFFER_PADDING_SIZE);
                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 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_H261 ||
             st->codec->codec_id == CODEC_ID_VORBIS ||
             st->codec->codec_id == CODEC_ID_MJPEG ||
             st->codec->codec_id == CODEC_ID_PNG ||
             st->codec->codec_id == CODEC_ID_PAM ||
             st->codec->codec_id == CODEC_ID_PGM ||
             st->codec->codec_id == CODEC_ID_PGMYUV ||
             st->codec->codec_id == CODEC_ID_PBM ||
             st->codec->codec_id == CODEC_ID_PPM ||
             st->codec->codec_id == CODEC_ID_SHORTEN ||
             (st->codec->codec_id == CODEC_ID_MPEG4 && !st->need_parsing))*/)
            try_decode_frame(st, pkt->data, pkt->size);

        if (st->time_base.den > 0 && av_rescale_q(codec_info_duration[st->index], st->time_base, AV_TIME_BASE_Q) >= ic->max_analyze_duration) {
            break;
        }
        count++;
    }

    // close codecs which where opened in try_decode_frame()
    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if(st->codec->codec)
            avcodec_close(st->codec);
    }
    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if (st->codec->codec_type == CODEC_TYPE_VIDEO) {
            if(st->codec->codec_id == CODEC_ID_RAWVIDEO && !st->codec->codec_tag && !st->codec->bits_per_sample)
                st->codec->codec_tag= avcodec_pix_fmt_to_codec_tag(st->codec->pix_fmt);

            if(duration_count[i]
               && (st->codec->time_base.num*101LL <= st->codec->time_base.den || st->codec->codec_id == CODEC_ID_MPEG2VIDEO) /*&&
               //FIXME we should not special case mpeg2, but this needs testing with non mpeg2 ...
               st->time_base.num*duration_sum[i]/duration_count[i]*101LL > st->time_base.den*/){
                double best_error= 2*av_q2d(st->time_base);
                best_error= best_error*best_error*duration_count[i]*1000*12*30;

                for(j=1; j<MAX_STD_TIMEBASES; j++){
                    double error= duration_error[i][j] * get_std_framerate(j);
//                    if(st->codec->codec_type == CODEC_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;
                        av_reduce(&st->r_frame_rate.num, &st->r_frame_rate.den, get_std_framerate(j), 12*1001, INT_MAX);
                    }
                }
            }

            if (!st->r_frame_rate.num){
                if(    st->codec->time_base.den * (int64_t)st->time_base.num
                    <= st->codec->time_base.num * (int64_t)st->time_base.den){
                    st->r_frame_rate.num = st->codec->time_base.den;
                    st->r_frame_rate.den = st->codec->time_base.num;
                }else{
                    st->r_frame_rate.num = st->time_base.den;
                    st->r_frame_rate.den = st->time_base.num;
                }
            }
        }else if(st->codec->codec_type == CODEC_TYPE_AUDIO) {
            if (st->codec->codec_id == CODEC_ID_NONE && probe_data[st->index].buf_size > 0) {
                codec_identified[st->index] = set_codec_from_probe_data(st, &(probe_data[st->index]), 1);
                if (codec_identified[st->index]) {
                    st->need_parsing = AVSTREAM_PARSE_FULL;
                }
            }
            if(!st->codec->bits_per_sample)
                st->codec->bits_per_sample= av_get_bits_per_sample(st->codec->codec_id);
        }
    }

    av_estimate_timings(ic, old_offset);

    for(i=0;i<ic->nb_streams;i++) {
        st = ic->streams[i];
        if (codec_identified[st->index])
            break;
    }
    //FIXME this is a mess
    if(i!=ic->nb_streams){
        av_read_frame_flush(ic);
        for(i=0;i<ic->nb_streams;i++) {
            st = ic->streams[i];
            if (codec_identified[st->index]) {
                av_seek_frame(ic, st->index, 0.0, 0);