请以json格式回答：尼康D750和佳能5D Mark IV的主要功能差异是什么？
user
```json
{
  "CameraModels": [
    {
      "Model": "Nikon D750",
      "Sensor": "24.3 MP Full-frame CMOS",
      "Processor": "EXPEED 4",
      "VideoResolution": "1080p up to 60 fps",
      "ISO": "100-12800 (expandable to 50-51200)",
      "AutofocusSystem": "51-point AF system"
    },
    {
      "Model": "Canon 5D Mark IV",
      "Sensor": "30.4 MP Full-frame CMOS",
      "Processor": "DIGIC 6+",
      "VideoResolution": "4K up to 30 fps",
      "ISO": "100-32000 (expandable to 50-102400)",
      "AutofocusSystem": "61-point AF system"
    }
  ],
  "Differences": [
    {
      "Category": "Sensor Resolution",
      "Nikon D750": "24.3 MP",
      "Canon 5D Mark IV": "30.4 MP"
    },
    {
      "Category": "Processor",
      "Nikon D750": "EXPEED 4",
      "Canon 5D Mark IV": "DIGIC 6+"
    },
    {
      "Category": "Video Resolution",
      "Nikon D750": "1080p up to 60 fps",
      "Canon 5D Mark IV": "4K up to 30 fps"
    },
    {
      "Category": "ISO Range",
      "Nikon D750": "100-12800 (expandable to 50-51200)",
      "Canon 5D Mark IV": "100-32000 (expandable to 50-102400)"
    },
    {
      "Category": "Autofocus System",
      "Nikon D750": "51-point AF system",
      "Canon 5D Mark IV": "61-point AF system"
    }
  ]
}
```
assistant