WebRTC: Support publish with pure video or audio stream. How to only publish video or only publish audio.

[shinoi2]

Description'

Please ensure that the markdown structure is maintained.

Description of the issue encountered:
I hope to be able to push only video or only audio when using Webrtc for streaming.
SRS version: v4.0.95
SRS configuration (Config): rtc2rtmp.conf

Reproduction:

Steps to reproduce the bug:
For example, if I only have a microphone and no camera, I can choose to only transmit audio. Here is an example of only transmitting audio:

1. Comment out the camera-related code in srs.sdk.js.
2. Start SRS.

    self.constraints = {
        audio: true,
        // video: {
        //     width: {ideal: 320, max: 576}
        // }
    };
    // self.pc.addTransceiver("video", {direction: "sendonly"});
    // self.pc.addTransceiver("video", {direction: "recvonly"});

2. At this point, WebRTC can transmit only audio and play pure audio. However, the RTMP stream cannot be played, and the third-party WebRTC (jswebrtc) cannot play it either.

3. If audio is commented out and only video is transmitted, WebRTC can transmit only video and play pure video. However, the RTMP stream has a large playback delay (about 6 seconds), the third-party WebRTC (jswebrtc) cannot play it, and it causes the SRS service to crash.

Expected Behavior (Expect)

Can push only video or only audio normally, and can play normally.

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[shinoi2]

The reason for the error is that when webrtc only pushes audio, encoding fails when encountering NACK. It should be that NACK is not handled properly.

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[gyf19]

I also want to know if the app's Flutter version has this bug. Thank you.

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[winlinvip]

Welcome Patch.

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[strangemk2]

Can you only push audio to HLS? It seems like there is no logic for segmenting and generating AAC in the code.

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[SuperChrisliu]

Has this problem been resolved now? Test it out. Webrtc only pushes audio, rtmp pulling is possible, but it takes about 7 seconds for rtmp to receive data.

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[winlinvip]

Already fixed by #3964. To use this feature, should upgrade to latest SRS player, allowing user to select audio or video only.