如果直接给std::vector<Struct> 定义时就赋值，出现：
error: could not convert ‘{{"audio", "audio/opus", 0, 48000}}’ from ‘<brace-enclosed initializer list>’ to ‘std::vector<RtpCodecCapability>’

例如下代码：

#include <vector>
#include <string>
#include <iostream>

struct RtpCodecCapability {
    std::string kind;
    std::string mimeType;
    int preferredPayloadType = 0;
    int clockRate = 0;
};

struct RtpCapabilities {
    std::vector<RtpCodecCapability> codecs;
};

const RtpCapabilities supportedRtpCapabilities = {
    // codecs
    {
        {
            "audio",        // kind
            "audio/opus",   // mimeType
            0,              // preferredPayloadType
            48000,          // clockRate
        },
        {
            "audio",        // kind
            "audio/opus",   // mimeType
            0,              // preferredPayloadType
            48000,          // clockRate
        },
        {
            "audio",        // kind
            "audio/opus",   // mimeType
            0,              // preferredPayloadType
            48000,          // clockRate
        },
    },
};

int main() {
    std::cout << "codes size " << supportedRtpCapabilities.codecs.size()  << std::endl;
    return 0;
}

编译选项：g++ -std=c++11 -o main main.cpp
解决办法：
调整为c++14可以通过，g++ -std=c++14 -o main main.cpp