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migrate_v4_CN_rtmp atc

winlin edited this page Jul 31, 2022 · 1 revision

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ATC支持HLS/HDS热备

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RTMP的热备怎么做?当边缘回源时,上层出现故障,可以切换到另外一个上层,所以RTMP热备只需要指定多个上层/源站就可以。边缘在故障切换时,会重新连接新服务器,客户端连接还没有断开,所以看起来就像是编码器重新推流了,画面最多抖动一下或者卡一下。

HLS热备怎么做?边缘从某个源站拿不到ts切片时,会去另外一个服务器拿。所以就要求两个上层的ts切片一样,当然如果上层服务器都从一个源站取片,是没有问题的。

如果HLS的源站需要做热备,怎么办?参考:Adobe: HDS/HLS热备,如下图所示:

                        +----------+        +----------+
               +--ATC->-+  server  +--ATC->-+ packager +-+   +---------+
+----------+   | RTMP   +----------+ RTMP   +----------+ |   | Reverse |    +-------+
| encoder  +->-+                                         +->-+  Proxy  +-->-+  CDN  +
+----------+   |        +----------+        +----------+ |   | (nginx) |    +-------+
               +--ATC->-+  server  +--ATC->-+ packager +-+   +---------+
                 RTMP   +----------+ RTMP   +----------+

实际上,adobe文中所说的是encoder输出的是ATC RTMP流,也没有packager直接server就打包了。如果你需要自己做打包,譬如基于ffmpeg写个工具,自定义HLS流的打包,编码器可以将ATC RTMP流推送到SRS,SRS会以ATC RTMP形式不修改时间戳分发给你的工具。

所以ATC RTMP说白了就是绝对时间,server需要能接入绝对时间,若切片在server上则根据绝对时间切片,若server和ReverseProxy之间还有切片工具,那server应该给切片工具绝对时间。

SRS配置ATC

SRS默认ATC是关闭,即给客户端的RTMP流永远从0开始。若工具需要SRS不修改时间戳(只将sequence header和metadata调整为第一个音视频包的时间戳),可以打开ATC配置:

vhost __defaultVhost__ {
    # for play client, both RTMP and other stream clients,
    # for instance, the HTTP FLV stream clients.
    play {
        # vhost for atc for hls/hds/rtmp backup.
        # generally, atc default to off, server delivery rtmp stream to client(flash) timestamp from 0.
        # when atc is on, server delivery rtmp stream by absolute time.
        # atc is used, for instance, encoder will copy stream to master and slave server,
        # server use atc to delivery stream to edge/client, where stream time from master/slave server
        # is always the same, client/tools can slice RTMP stream to HLS according to the same time,
        # if the time not the same, the HLS stream cannot slice to support system backup.
        # 
        # @see http://www.adobe.com/cn/devnet/adobe-media-server/articles/varnish-sample-for-failover.html
        # @see http://www.baidu.com/#wd=hds%20hls%20atc
        #
        # default: off
        atc             off;
    }
}

ATC和flash的兼容性

开启ATC之后,flash客户端播放SRS流时,流的起始时间不是0而是ATC时间。需要调整时间的包:

  • sequence header: 调整为第一个音视频包的时间。若有gop cache,则调整为gop cache中的第一个音视频包的时间。
  • metadata: 调整为第一个音视频包的时间。nginx-rtmp没有调整metadata包的时间(为0),所以平均每20次就有一次卡死。

经过测试,SRS打开和关闭ATC,flash播放器都能播放SRS的RTMP流。

ATC和编码器

编码器开启atc之后,若在metadata中自动写入"bravo_atc"="true",srs会自动的开启atc。

可以禁用这个功能:

vhost atc.srs.com {
    # for play client, both RTMP and other stream clients,
    # for instance, the HTTP FLV stream clients.
    play {
        # whether enable the auto atc,
        # if enabled, detect the bravo_atc="true" in onMetaData packet,
        # set atc to on if matched.
        # always ignore the onMetaData if atc_auto is off.
        # default: off
        atc_auto        off;
    }
}

将自动atc关闭即可。

Winlin 2014.3

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