Ffplay源码之read_thread解析(二)

ic->interrupt_callback.callback = 
decode_interrupt_cb;
    ic->interrupt_callback.opaque = is;

static int decode_interrupt_cb(void *ctx)
{
    VideoState *is = ctx;
    return is->abort_request;
}

#0  decode_interrupt_cb (ctx=0x7ffff7e36040) at fftools/ffplay.c:2715
#1  0x00000000007d99b7 in ff_check_interrupt (cb=0x7fffd40012f0) at libavformat/avio.c:667
#2  retry_transfer_wrapper (transfer_func=0x7dd950 <file_read>, size_min=1, size=32768, buf=0x7fffd4001540 "", h=0x7fffd40012c0) at libavformat/avio.c:374
#3  ffurl_read (h=0x7fffd40012c0, buf=0x7fffd4001540 "", size=32768) at libavformat/avio.c:411
#4  0x000000000068cd9c in read_packet_wrapper (size=<optimized out>, buf=<optimized out>, s=0x7fffd40095c0) at libavformat/aviobuf.c:535
#5  fill_buffer (s=0x7fffd40095c0) at libavformat/aviobuf.c:584
#6  avio_read (s=s@entry=0x7fffd40095c0, buf=0x7fffd40096d0 "@\225", size=size@entry=2048) at libavformat/aviobuf.c:677
#7  0x00000000006b7780 in av_probe_input_buffer2 (pb=0x7fffd40095c0, fmt=0x7fffd4000948, filename=filename@entry=0x36429b0 "../../share/2_audio.mp4", 
    logctx=logctx@entry=0x7fffd4000940, offset=offset@entry=0, max_probe_size=1048576) at libavformat/format.c:262
#8  0x00000000007b631d in init_input (options=0x7fffe19b6b50, filename=0x36429b0 "../../share/2_audio.mp4", s=0x7fffd4000940) at libavformat/utils.c:443
#9  avformat_open_input (ps=ps@entry=0x7fffe19b6bf8, filename=0x36429b0 "../../share/2_audio.mp4", fmt=<optimized out>, options=0x2e38450 <format_opts>)
    at libavformat/utils.c:573

//特定选项处理
 if (!av_dict_get(format_opts, "scan_all_pmts", NULL, AV_DICT_MATCH_CASE)) {
        av_dict_set(&format_opts, "scan_all_pmts", "1", AV_DICT_DONT_OVERWRITE);
        scan_all_pmts_set = 1;
    }
    err = avformat_open_input(&ic, is->filename, is->iformat, &format_opts);
    if (err < 0) {
        print_error(is->filename, err);
        ret = -1;
        goto fail;
    }
    
if (scan_all_pmts_set)
        av_dict_set(&format_opts, "scan_all_pmts", NULL, AV_DICT_MATCH_CASE);

    if ((t = av_dict_get(format_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;
    }    
    

/**
 * Open an input stream and read the header. The codecs are not opened.
 * The stream must be closed with avformat_close_input().
 *
 * @param ps Pointer to user-supplied AVFormatContext (allocated by avformat_alloc_context).
 *           May be a pointer to NULL, in which case an AVFormatContext is allocated by this
 *           function and written into ps.
 *           Note that a user-supplied AVFormatContext will be freed on failure.
 * @param url URL of the stream to open.
 * @param fmt If non-NULL, this parameter forces a specific input format.
 *            Otherwise the format is autodetected.
 * @param options  A dictionary filled with AVFormatContext and demuxer-private options.
 *                 On return this parameter will be destroyed and replaced with a dict containing
 *                 options that were not found. May be NULL.
 *
 * @return 0 on success, a negative AVERROR on failure.
 *
 * @note If you want to use custom IO, preallocate the format context and set its pb field.
 */
int avformat_open_input(AVFormatContext **ps, const char *url, ff_const59 AVInputFormat *fmt, AVDictionary **options);

  /*  检测是否指定播放起始时间 */
    if (start_time != AV_NOPTS_VALUE) {
        int64_t timestamp;

        timestamp = start_time;
        /* add the stream start time */
        if (ic->start_time != AV_NOPTS_VALUE)
            timestamp += ic->start_time;
        // seek的指定的位置开始播放
        ret = avformat_seek_file(ic, -1, INT64_MIN, timestamp, INT64_MAX, 0);
        if (ret < 0) {
            av_log(NULL, AV_LOG_WARNING, "%s: could not seek to position %0.3f\n",
                   is->filename, (double)timestamp / AV_TIME_BASE);
        }
    }

//从待处理流中获取相关参数，设置显示窗⼝的宽度、⾼度及宽⾼⽐
is->show_mode = show_mode;
    if (st_index[AVMEDIA_TYPE_VIDEO] >= 0) {
        AVStream *st = ic->streams[st_index[AVMEDIA_TYPE_VIDEO]];
        AVCodecParameters *codecpar = st->codecpar;
 //根据流和帧宽⾼⽐猜测帧的样本宽⾼⽐。
 //由于帧宽⾼⽐由解码器设置，但流宽⾼⽐由解复⽤器设置，因此这两者可能不相 等。
//此函数会尝试返回待显示帧应当使⽤的宽⾼⽐值。
//基本逻辑是优先使⽤流宽⾼⽐(前提是值是合理的)，其次使⽤帧宽⾼⽐。
//这样，流宽⾼⽐(容器设置，易于修改)可以覆盖帧宽⾼⽐
        AVRational sar = av_guess_sample_aspect_ratio(ic, st, NULL);
        if (codecpar->width)
        // 设置显示窗⼝的⼤⼩和宽⾼⽐
            set_default_window_size(codecpar->width, codecpar->height, sar);
    }

 /*  打开视频、音频解码器。在此会打开相应解码器，并创建相应的解码线程。 */
    if (st_index[AVMEDIA_TYPE_AUDIO] >= 0) {// 如果有音频流则打开音频流
        stream_component_open(is, st_index[AVMEDIA_TYPE_AUDIO]);
    }

    ret = -1;
    if (st_index[AVMEDIA_TYPE_VIDEO] >= 0) { // 如果有视频流则打开视频流
        ret = stream_component_open(is, st_index[AVMEDIA_TYPE_VIDEO]);
    }
    if (is->show_mode == SHOW_MODE_NONE) {
        //选择怎么显示，如果视频打开成功，就显示视频画面，否则，显示音频对应的频谱图
        is->show_mode = ret >= 0 ? SHOW_MODE_VIDEO : SHOW_MODE_RDFT;
    }

    if (st_index[AVMEDIA_TYPE_SUBTITLE] >= 0) { // 如果有字幕流则打开字幕流
        stream_component_open(is, st_index[AVMEDIA_TYPE_SUBTITLE]);
    }

    if (is->video_stream < 0 && is->audio_stream < 0) {
        av_log(NULL, AV_LOG_FATAL, "Failed to open file '%s' or configure filtergraph\n",
               is->filename);
        ret = -1;
        goto fail;
    }

a. 根据⽤户指定来查找流avformat_match_stream_specifier 
b. 使⽤av_find_best_stream查找流