How to open a file descriptor instead of AAsset in FFMpegExtractor?

[rafagan]

In examples, is available the class FFMpegExtractor, with callback methods int read(void *opaque, uint8_t *buf, int buf_size) and int64_t seek(void *opaque, int64_t offset, int whence). How can I replace the logic using AAsset to something more generic, like the std FILE type?