Video playback system and image display device

A video playback system comprising

• an image supply device configured to transmit video data;
• an image display device configured to receive the video data and play a video according to the video data;
• a first acquirer configured to acquire first specification information indicating video playback performance of the image display device;
• a second acquirer configured to acquire second specification information indicating video creating performance of the image supply device;
• a determiner configured to determine, based. on the first specification information and the second specification information, either the image display device or the image supply device to be a device satisfying a playback condition;
• and
• a controller configured to cause a converter of either the image display device or the image supply device determined to be the device satisfying the playback condition by the determiner to convert the video data into video data satisfying the playback condition, wherein
• when the playback condition is changed to a new playback condition while the image display device is playing a video, the controller causes the converter of the image display device to convert the video data into video data satisfying the new playback condition until the image display device receives video data where the new playback condition is reflected from the image supply device.