add custom output_params to export_to_video

[eyaler]

The export_to_video docstring mentions output_params: https://github.com/huggingface/diffusers/blob/v0.35.2/src/diffusers/utils/export_utils.py#L152, but this is not implemented, not allowing to pass custom params to ffmpeg.

[DN6]

Hi @eyaler I think that might be a mistake in the docstring. export_to_video is mostly a convenience utility function. If you need to access all of FFmpegs features, it would be better to save the individual frames as images and then use FFmpeg directly.

[eyaler]

@DN6 thanks! yes the docs can be fixed to elimante the mention, but there are some common useful options like movflags='faststart', pix_fmt='yuv420p' that I almost always want to use, so a generic **output_params could be convinient.