Something like:

```
./examples/heif-enc --params --encoder x265
```

should produce the list of parameters, but it produces a usage statement.

Instead, it needs the input file to get past the command line checks, even though it isn't using that file (and makes no output).
heif-enc requires input file to show parameters
This is a GitHub Issue
repo:libheif
owner:strukturag
Title : heif-enc requires input file to show parameters
Issue date:

--- start body ---
Something like:

```
./examples/heif-enc --params --encoder x265
```

should produce the list of parameters, but it produces a usage statement.

Instead, it needs the input file to get past the command line checks, even though it isn't using that file (and makes no output).
--- end body ---
