Issue with locked input fields in Sanity Studio and a solution involving adding a hidden field with a default value.

export default {
	name: 'project',
	title: 'Project',
	type: 'document',
	fields: [
		{
			name: 'video',
			title: 'Video (16:9)',
			type: 'object',
			validation: Rule => Rule.required(),
			fields: [
				{
					title: 'Video URL (16:9)',
					name: 'videoUrl',
					type: 'video',
				},
			],
		},
	],
};

export default {
	name: 'video',
	title: 'Video',
	icon: Icon,
	type: 'object',
	fields: [
		{
			name: 'title',
			title: 'Title',
			type: 'string',
		},
		{
			name: 'videoId',
			title: 'Video ID (Vimeo)',
			type: 'string',
			validation: Rule => Rule.required(),
		},
		{
			name: 'showControls',
			title: 'Show Controls?',
			type: 'boolean',
		},
	],
};