播放器系列之ffplay源码分析（三）

这里开始调用解码线程audio_thread()、video_thread()、subtitle_thread()

/* open a given stream. Return 0 if OK */
static int stream_component_open(VideoState *is, int stream_index)
{
    AVFormatContext *ic = is->ic;
    AVCodecContext *avctx;
    AVCodec *codec;
    const char *forced_codec_name = NULL;
    AVDictionary *opts = NULL;
    AVDictionaryEntry *t = NULL;
    int sample_rate, nb_channels;
    int64_t channel_layout;
    int ret = 0;
    int stream_lowres = lowres;

    if (stream_index < 0 || stream_index >= ic->nb_streams)
        return -1;

    avctx = avcodec_alloc_context3(NULL);
    if (!avctx)
        return AVERROR(ENOMEM);

    ret = avcodec_parameters_to_context(avctx, ic->streams[stream_index]->codecpar);
    if (ret < 0)
        goto fail;
    avctx->pkt_timebase = ic->streams[stream_index]->time_base;

    codec = avcodec_find_decoder(avctx->codec_id);

    switch(avctx->codec_type){
        case AVMEDIA_TYPE_AUDIO   : is->last_audio_stream    = stream_index; forced_codec_name =    audio_codec_name; break;
        case AVMEDIA_TYPE_SUBTITLE: is->last_subtitle_stream = stream_index; forced_codec_name = subtitle_codec_name; break;
        case AVMEDIA_TYPE_VIDEO   : is->last_video_stream    = stream_index; forced_codec_name =    video_codec_name; break;
    }
    if (forced_codec_name)
        codec = avcodec_find_decoder_by_name(forced_codec_name);
    if (!codec) {
        if (forced_codec_name) av_log(NULL, AV_LOG_WARNING,
                                      "No codec could be found with name '%s'\n", forced_codec_name);
        else                   av_log(NULL, AV_LOG_WARNING,
                                      "No decoder could be found for codec %s\n", avcodec_get_name(avctx->codec_id));
        ret = AVERROR(EINVAL);
        goto fail;
    }

    avctx->codec_id = codec->id;
    if (stream_lowres > codec->max_lowres) {
        av_log(avctx, AV_LOG_WARNING, "The maximum value for lowres supported by the decoder is %d\n",
                codec->max_lowres);
        stream_lowres = codec->max_lowres;
    }
    avctx->lowres = stream_lowres;

    if (fast)
        avctx->flags2 |= AV_CODEC_FLAG2_FAST;

    opts = filter_codec_opts(codec_opts, avctx->codec_id, ic, ic->streams[stream_index], codec);
    if (!av_dict_get(opts, "threads", NULL, 0))
        av_dict_set(&opts, "threads", "auto", 0);
    if (stream_lowres)
        av_dict_set_int(&opts, "lowres", stream_lowres, 0);
    if (avctx->codec_type == AVMEDIA_TYPE_VIDEO || avctx->codec_type == AVMEDIA_TYPE_AUDIO)
        av_dict_set(&opts, "refcounted_frames", "1", 0);
    if ((ret = avcodec_open2(avctx, codec, &opts)) < 0) {
        goto fail;
    }
    if ((t = av_dict_get(opts, "", NULL, AV_DICT_IGNORE_SUFFIX))) {
        av_log(NULL, AV_LOG_ERROR, "Option %s not found.\n", t->key);
        ret =  AVERROR_OPTION_NOT_FOUND;
        goto fail;
    }

    is->eof = 0;
    ic->streams[stream_index]->discard = AVDISCARD_DEFAULT;
    switch (avctx->codec_type) {
    case AVMEDIA_TYPE_AUDIO:
#if CONFIG_AVFILTER
        {
            AVFilterContext *sink;

            is->audio_filter_src.freq           = avctx->sample_rate;
            is->audio_filter_src.channels       = avctx->channels;
            is->audio_filter_src.channel_layout = get_valid_channel_layout(avctx->channel_layout, avctx->channels);
            is->audio_filter_src.fmt            = avctx->sample_fmt;
            if ((ret = configure_audio_filters(is, afilters, 0)) < 0)
                goto fail;
            sink = is->out_audio_filter;
            sample_rate    = av_buffersink_get_sample_rate(sink);
            nb_channels    = av_buffersink_get_channels(sink);
            channel_layout = av_buffersink_get_channel_layout(sink);
        }
#else
        sample_rate    = avctx->sample_rate;
        nb_channels    = avctx->channels;
        channel_layout = avctx->channel_layout;
#endif

        /* prepare audio output */
        if ((ret = audio_open(is, channel_layout, nb_channels, sample_rate, &is->audio_tgt)) < 0)
            goto fail;
        is->audio_hw_buf_size = ret;
        is->audio_src = is->audio_tgt;
        is->audio_buf_size  = 0;
        is->audio_buf_index = 0;

        /* init averaging filter */
        is->audio_diff_avg_coef  = exp(log(0.01) / AUDIO_DIFF_AVG_NB);
        is->audio_diff_avg_count = 0;
        /* since we do not have a precise anough audio FIFO fullness,
           we correct audio sync only if larger than this threshold */
        is->audio_diff_threshold = (double)(is->audio_hw_buf_size) / is->audio_tgt.bytes_per_sec;

        is->audio_stream = stream_index;
        is->audio_st = ic->streams[stream_index];

        decoder_init(&is->auddec, avctx, &is->audioq, is->continue_read_thread);
        if ((is->ic->iformat->flags & (AVFMT_NOBINSEARCH | AVFMT_NOGENSEARCH | AVFMT_NO_BYTE_SEEK)) && !is->ic->iformat->read_seek) {
            is->auddec.start_pts = is->audio_st->start_time;
            is->auddec.start_pts_tb = is->audio_st->time_base;
        }
        if ((ret = decoder_start(&is->auddec, audio_thread, is)) < 0)
            goto out;
        SDL_PauseAudioDevice(audio_dev, 0);
        break;
    case AVMEDIA_TYPE_VIDEO:
        is->video_stream = stream_index;
        is->video_st = ic->streams[stream_index];

        decoder_init(&is->viddec, avctx, &is->videoq, is->continue_read_thread);
        if ((ret = decoder_start(&is->viddec, video_thread, is)) < 0)
            goto out;
        is->queue_attachments_req = 1;
        break;
    case AVMEDIA_TYPE_SUBTITLE:
        is->subtitle_stream = stream_index;
        is->subtitle_st = ic->streams[stream_index];

        decoder_init(&is->subdec, avctx, &is->subtitleq, is->continue_read_thread);
        if ((ret = decoder_start(&is->subdec, subtitle_thread, is)) < 0)
            goto out;
        break;
    default:
        break;
    }
    goto out;

fail:
    avcodec_free_context(&avctx);
out:
    av_dict_free(&opts);

    return ret;
}