WebRTC: Support stereo in SDP answer for players

[superyhee]

Note: Please read FAQ before file an issue, see #2716

Description

Please description your issue here

1. SRS Version: v5.0-a4
2. SRS Log:

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3. SRS Config:

   rtc { enabled on;

   @see https://github.com/ossrs/srs/wiki/v4_CN_WebRTC#rtmp-to-rtc

   rtmp_to_rtc on;
   # @see https://github.com/ossrs/srs/wiki/v4_CN_WebRTC#rtc-to-rtmp
   rtc_to_rtmp on;
   keep_bframe off; 

   } `

Expect

通过rtc使用音乐文件推流，用rtc拉流或者rtc2rtmp拉流，音频不是立体声，需要在sdp的a=ftmp这一行中加入stereo=1代表双声道，stereo=0代表单声道 a=fmtp:111 minptime=10;useinbandfec=1; stereo=1; maxaveragebitrate=192000 我在客户端使用了下面的方式 async function run() { const offer = await peerConnection.createOffer(); offer.sdp = offer.sdp.replace('useinbandfec=1', 'useinbandfec=1; stereo=1; sprop-stereo=1;stereo=1; maxaveragebitrate=192000') await peerConnection.setLocalDescription(offer) 服务器端是否可以通过配置来支持stereo=1？

[winlinvip]

This is a feature, please update your issue and describe more details about the backgroud and use scenarios, or we will delete it.

[superyhee]

主要的使用场景是用rtc来实现网页直播，需要在直播中播放高质量的音乐，比如直播中播放立体声音乐，目前srs用rtc或者rtc2rtmp播放不是立体声