一 ffmpeg几乎是万能的,很多人会用ffmpeg用来做流媒体协议解析。接口统一,调用非常方便
调用示例:
av_register_all();
avformat_network_init();//注册网络流格式
avformat_network_init();//注册网络流格式
avformat_alloc_context();//申请流格式上下文
avformat_find_stream_info(ctx, 0)
dump_stream_format(ctx);//dump 流信息
av_read_frame(ctx,AVPacket);
一般打开慢是在 avformat_find_stream_info(ctx, 0) 函数调用。
看看ffmpeg的具体实现
for (i = 0; i < ic->nb_streams; i++) {
const AVCodec *codec;
AVDictionary *thread_opt = NULL;
st = ic->streams[i];
avctx = st->internal->avctx;
}
const AVCodec *codec;
AVDictionary *thread_opt = NULL;
st = ic->streams[i];
avctx = st->internal->avctx;
for (i = 0; i < ic->nb_streams; i++) {
int fps_analyze_framecount = 20;
st = ic->streams[i];
if (!has_codec_parameters(st, NULL))
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;//一般我们设置的是这个时间基,40帧
if (!tb_unreliable(st->internal->avctx))
fps_analyze_framecount = 0;
if (ic->fps_probe_size >= 0)
fps_analyze_framecount = ic->fps_probe_size;
if (st->disposition & AV_DISPOSITION_ATTACHED_PIC)
fps_analyze_framecount = 0;
/* variable fps and no guess at the real fps */
if (!(st->r_frame_rate.num && st->avg_frame_rate.num) &&
st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
int count = (ic->iformat->flags & AVFMT_NOTIMESTAMPS) ?
st->info->codec_info_duration_fields/2 :
st->info->duration_count;
if (count < fps_analyze_framecount)
break;
}
if (st->parser && st->parser->parser->split &&
!st->internal->avctx->extradata)
break;
if (st->first_dts == AV_NOPTS_VALUE &&
!(ic->iformat->flags & AVFMT_NOTIMESTAMPS) &&
st->codec_info_nb_frames < ((st->disposition & AV_DISPOSITION_ATTACHED_PIC) ? 1 : ic->max_ts_probe) &&
(st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO))
break;
}
analyzed_all_streams = 0;
if (!missing_streams || !*missing_streams)
if (i == ic->nb_streams) {
analyzed_all_streams = 1;
/* 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");
flush_codecs = 0;
break;
}
int fps_analyze_framecount = 20;
st = ic->streams[i];
if (!has_codec_parameters(st, NULL))
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;//一般我们设置的是这个时间基,40帧
if (!tb_unreliable(st->internal->avctx))
fps_analyze_framecount = 0;
if (ic->fps_probe_size >= 0)
fps_analyze_framecount = ic->fps_probe_size;
if (st->disposition & AV_DISPOSITION_ATTACHED_PIC)
fps_analyze_framecount = 0;
/* variable fps and no guess at the real fps */
if (!(st->r_frame_rate.num && st->avg_frame_rate.num) &&
st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {
int count = (ic->iformat->flags & AVFMT_NOTIMESTAMPS) ?
st->info->codec_info_duration_fields/2 :
st->info->duration_count;
if (count < fps_analyze_framecount)
break;
}
if (st->parser && st->parser->parser->split &&
!st->internal->avctx->extradata)
break;
if (st->first_dts == AV_NOPTS_VALUE &&
!(ic->iformat->flags & AVFMT_NOTIMESTAMPS) &&
st->codec_info_nb_frames < ((st->disposition & AV_DISPOSITION_ATTACHED_PIC) ? 1 : ic->max_ts_probe) &&
(st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO))
break;
}
analyzed_all_streams = 0;
if (!missing_streams || !*missing_streams)
if (i == ic->nb_streams) {
analyzed_all_streams = 1;
/* 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");
flush_codecs = 0;
break;
}
从代码可以看出来,在没有音频帧的情况下,需要读取40帧才会返回。
很多安防设备没有音频,所以这里可以自行解析数据以快速得到画面。