It might be good to create a separate source files for the configuration object.
core.cpp keeps growing.

I understand the necessity to trim out the fat of core.cpp, but this better be done as a planned initiative, not ad-hoc.

Confirming the idea to have srt_create_config and srt_delete_config to create and delete an object, while srt_config_add adds entry to the object.
This looks aligned to the existing API:

• srt_setsockopt(..)
• srt_create_socket(..)

After the connection process only those objects should be deleted that weren't reset to NULL.

I think the deletion of the object should be done by the upstream app.
This is the mission of srt_delete_config(..).

The idea is that the configuration object should only be deleted in case when you decided that you don't need to make a connection. Don't forget that this is a C API and any simplification here will be welcome.

In short: you need to perform deletion only if this object has been created, but you are somehow unable to call the srt_connect_group function. If you know prematurely that you WILL pass this object to the structure passed to this function, you don't have to delete it at all. This function is simply provided for completion because we cannot leave a user with no possibility to delete an object and just sentenced to call the connect function anyway, or live with a leak.

Just as an additional help, pointers to objects that have been "eaten up" by the connection function are reset to NULL. So the user should simply fill the config field with the result of srt_create_config() directly, and call srt_delete_config() on all of them, if they aren't certain if they called srt_connect_group().

Usage example

SRT_SOCKGROUPCONFIG data [] = {
    srt_prepare_endpoint( ... 1 ... ),
    srt_perpare_endpoint( ... 2 ... )
};

data[0].config = srt_create_config(); 
srt_config_add(data[0].config, SRT_BINDTODEVICE, "eth0", 4);

data[1].config = srt_create_config();
srt_config_add(data[1].config, SRT_BINDTODEVICE, "eth1", 4);

size_t len = sizeof data;
srt_connect_group(grp, data, len);

// if srt_connect_group suceeded, then data[i].config will be nullptr
for (auto& d: data)
    srt_delete_config(d.config);

Sharing the same config is prohibited, and will cause a crash(?)

SRT_SOCKGROUPCONFIG data [] = {
    srt_prepare_endpoint( ... 1 ... ),
    srt_perpare_endpoint( ... 2 ... )
};

SRT_SOCKOPT_CONFIG* config = srt_create_config();
srt_config_add(config, SRT_BINDTODEVICE, "eth0", sizeof int);

data[0].config = config;
data[1].config = config;

size_t len = sizeof data;
// Crash on deleting already deleted obect
srt_connect_group(grp, data, len);

// if srt_connect_group suceeded, then data[i].config will be nullptr
for (auto& d: data)
    srt_delete_config(d.config);

In the current proposal, IF srt_connect_group was called (no matter if succeeded or failed), objects will be deleted. Manual deletion would be only necessary if - by some reason - you created the object, but you didn't call srt_connect_group.