HT2519: Download past purchasesLearn about Download past purchases
Currently Being ModeratedJun 24, 2013 6:12 AM (in response to jill146)
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The following articles may provide more information in relation to your question:
HD videos feature a higher-quality picture, but are designed to be played only on your iPhone 4 or later, iPod touch (4th generation), iPad, iPad 2, computer, or Apple TV. HD content is offered in either 720p or 1080p.
When you purchase an HD video on a supported device or computer, only HD video will be downloaded. To download the SD version, you need to download the video again from your Purchased page. Conversely, if you purchase an HD video on an unsupported device, the SD version will be downloaded. Then, you will need to download the HD version from your Purchased page.