You refer to the documentation and say new streammux can’t accept different resolutions.
In the documentation it is said:
New nvstreammux do not transform/scale batched buffers to a single color-format/resolution unlike the default nvstreammux. A batch can have buffers from different streams of different resolutions and formats.
Also:
When we have plugins that could transform the input buffers (example: change resolution or color format of video buffers in the batch) between nvstreammux and nvstreamdemux, we need to ensure nvstreammux output is homogeneous (meaning buffers from all sources in the batch shall have same resolution and color format). This is a limitation in the new nvstreammux and shall be addressed in upcoming releases.
I am not using nvstreamdemux, so the documentation is not clear at all.