Transaction insertion and uniqueness constraints, is the latter inserter reporting an error or blocking?

There is such a table:

 CREATE TABLE `tiny_url` (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `user_id` int NOT NULL,
  `short_uuid` varchar(255) NOT NULL,
  `video_id` int NOT NULL,
  `created_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  `updated_at` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
  PRIMARY KEY (`id`),
  UNIQUE KEY `tinyurl_short_uuid` (`short_uuid`),
  UNIQUE KEY `tinyurl_user_id_video_id` (`user_id`,`video_id`)
) ENGINE=InnoDB AUTO_INCREMENT=26 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

Operation 1: I use SQL in a transaction:
begin First opening is a transaction, then select insert:
insert into tiny_url (user_id,video_id,short_uuid) values (100,300,'ilikeyou')

Operation two: and use another SQL in another transaction: insert into tiny_url (user_id,video_id,short_uuid) values (100,300,'ilikeyou too')

Because there is a unique constraint UNIQUE KEY tinyurl_user_id_video_id ( user_id , video_id ) , so, do you think, will operate two error or jam?

The answer is blocking.

What happens if operation one is executing commit at this moment?
Answer: Operation 1 is successfully inserted, and operation 2 reports an error

What happens if operation one is executing rollback at this moment?
Answer: The first operation is rolled back successfully, and the second operation is inserted successfully