To generate the patch for the given code slice with a CWE-401 (Memory Leak) vulnerability, we can follow these reasoning steps:

### Step 1: Root Cause Analysis

- 1: Identify the Resource:
  - The code is dealing with `RTSPStream` objects, which are stored in the `rt->rtsp_streams` array.
  - Each `RTSPStream` object is dynamically allocated and needs to be freed when it's no longer needed.

- 2: Resource Allocation and Deallocation:
  - The `RTSPStream` objects are allocated dynamically, but there's no clear indication of when they are freed.
  - The `av_free(rt->rtsp_streams)` call at line 18 frees the array itself, but not the individual `RTSPStream` objects it contains.

- 3: Potential Vulnerability:
  - The vulnerability arises because the `RTSPStream` objects are not being freed individually.
  - This results in a memory leak, as the memory allocated for each `RTSPStream` object is not being released back to the system.

### Conclusion:
The vulnerable behavior in this code is a memory leak. It occurs because the `RTSPStream` objects are not being freed individually, leading to memory not being released back to the system. To fix this, we need to ensure that each `RTSPStream` object is freed when it's no longer needed.

### Step 2: Fixing Strategy

- A common fixing strategy for memory leaks is to ensure that every dynamically allocated resource is freed when it's no longer needed.
- In this case, we need to add a call to `av_free` for each `RTSPStream` object after it's been processed.
- This can be done by adding the following lines of code after the `if (rtsp_st)` block:
  ```c
av_free(rtsp_st);
```
- This ensures that each `RTSPStream` object is freed individually, preventing the memory leak.

The resulting patch is:
```c
<             }
<         }
---
>             }
>             av_free(rtsp_st);
>         }
```
This patch fixes the memory leak by freeing each `RTSPStream` object individually, ensuring that the memory allocated for these objects is released back to the system.