Potential memory leak in [ff_dmx.c](https://github.com/gpac/gpac/blob/master/src/filters/ff_dmx.c) line 1728 and 1736. Calling av_dict_set()  without calling av_dict_free() to free the memory will cause a memory leak. [Doc](https://ffmpeg.org/doxygen/trunk/group__lavu__dict.html#ga1bafd682b1fbb90e48a4cc3814b820f7) says "av_dict_free() Free all the memory allocated for an [AVDictionary](https://ffmpeg.org/doxygen/trunk/structAVDictionary.html) struct and all keys and values."
![image](https://user-images.githubusercontent.com/39425646/214519771-6f562018-702e-41ce-b83e-e5b4c0c0c158.png)

Potential memory leak in src/filters/ff_dmx.c
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Potential memory leak in src/filters/ff_dmx.c
Issue date:

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Potential memory leak in [ff_dmx.c](https://github.com/gpac/gpac/blob/master/src/filters/ff_dmx.c) line 1728 and 1736. Calling av_dict_set()  without calling av_dict_free() to free the memory will cause a memory leak. [Doc](https://ffmpeg.org/doxygen/trunk/group__lavu__dict.html#ga1bafd682b1fbb90e48a4cc3814b820f7) says "av_dict_free() Free all the memory allocated for an [AVDictionary](https://ffmpeg.org/doxygen/trunk/structAVDictionary.html) struct and all keys and values."
![image](https://user-images.githubusercontent.com/39425646/214519771-6f562018-702e-41ce-b83e-e5b4c0c0c158.png)

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