secondary channel format

secondary channel format

reversed by omarroth on #invidious. his message:
The channel you sent me uses a different format. YouTube uses:
```json
{
  "80226972:0:embedded": {
    "2:0:string": "UC6Om9kAkl32dWlDSNlDS9Iw",
    "3:1:base64": {
      "2:0:string": "videos",
      "3:1:varint": 3,
      "4:2:varint": 0,
      "6:3:varint": 1,
      "7:4:varint": 1,
      "61:5:base64": {
        "1:0:embedded": {
          "2:1:embedded": {
            "1:0:base64": {
              "1:0:varint": 120
            }
          }
        }
      }
    }
  }
}
```

where `"1:0:varint": 120` is the offset into the channel.