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We are developing an educational tablet-app for our customer. The app is required to show fullscreen videos of university style lectures In-App. After a short introductory phase, where the lecturer is introducing himself and the topic, only powerpoint slides are shown, with oral commentary by the lecturer.

Since we have to use MP4 videos, I'm looking for advice, be it scientifically evident or experience based, on which resolution the videos should have to make sure, that the text in it can be read properly on modern 10 inch tablets.

I've already looked around a bit and only found vague advice like "one level of screen-resolution below the tablets native screen-resolution", but I'd be interested in more elaborate answers towards that topic.

EDIT:

To answer some question that came up:

  • Do you have control over content strategy / production? -> Sadly not. We are getting the content directly by the lecturers and these guys are very stubborn when it comes to external advice.
  • Are there bandwidth/storage limitations on your side? -> Not directly on "our" side, but client-side there are the storage limitations of the tablet model that will be used. Since it'll almost certainly be a device with 32GB capacity, I think we are safe on this.
  • If you are using a custom player, are you able to provide multiple asset resolutions to handle different user bandwidths a la YouTube? -> That won't be possible, because the source material will only be existing in one format/size. (i.e. MP4/720p)

Thanks for the great feedback so far.

  • Are the videos streamed or stored locally? – Milo Oct 22 '14 at 7:21
  • @Milo They are stored locally. – plocks Oct 22 '14 at 7:22
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The 150 rule states that the ideal distance for reading text is 150 X the height of the font. So the source content will matter. If the source is not known, I would take best practices for power point font size and use a comfortable tablet viewing distance and base my content window size on this.

Ideally the computer video card producing the content will be set to the desired resolution on a dedicated output that is feeding the encoder. The pc should be set to extend displays. This should give the cleanest scaling.

A 10" tablet probably gives you a an angle (triangle between your eye ball and the top and bottom of a letter) similar to a 20" desktop monitor. So if the content looks good at 720p on a 1080p desktop monitor then it will probably look good at 720p on a 1080p native tablet... as an example.

I also agree with Danny in that viewing it first hand is the way to go.

  • Sadly the source content will differ (i.e. the font style and size) and we cannot manipulate it, but your rule of thumb seems to be a good point. I'm going to test that. – plocks Oct 22 '14 at 6:24
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Any resolution sufficiently high as to be able to render the text should be fine. People were successfully reading powerpoint presentations across a crowded hall using projectors in the mid 90s.

Using any modern HD resolution is more than sufficiently usable for your needs. I'd probably standardise on 720p, because you can guarantee that every current and last generation tablet will be able to view it correctly.

There are no UX implications at all to differentiate between using any of the various resolutions above 480p when all you're doing is displaying text and static pictures.

  • Yeah, it will almost only be text and pictures. Thanks for your feedback. – plocks Oct 21 '14 at 17:42
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I assume you're hosting your own videos and they will be streaming via a custom player (i.e. not using a service like YouTube or Vimeo embedded within a web-view)?

Some questions that come to mind are:

  • Do you have control over content strategy / production?
  • Are there bandwidth/storage limitations on your side?
  • If you are using a custom player, are you able to provide multiple asset resolutions to handle different user bandwidths a la YouTube?

From my experience, we've had to work through these types of questions from a tech perspective first to figure out what limitations we are working within, which then helps inform content strategy and design / production, which in turn allows us to iterate before implementation.

If you have the option for user testing with a target tablet and internet connection, seems like the best way would be to compress a sample video asset in a range of resolutions and test it on the lowest target screen resolution to find the lowest common denominator for the sweet spot between readability and a smooth video experience. I think seeing it first-hand will inform you better than any golden rule.

  • Thanks for your input, I've addressed your questions in mine :) – plocks Oct 22 '14 at 6:30
  • Great. For storage/bandwidth I was actually referring to the server hosting the files, not user-side with the tablet. If you are updating content frequently and they are all 1080p HD lectures that are 1 hour+ long videos, that's a huge amount of data to store and transmit. Given the subject matter, I'm assuming there isn't a limitless pool of funds lying around for hosting. Just mention it because it can definitely affect the user if the server gets backed up. – Danny F. Oct 22 '14 at 14:19
  • Also, re: multiple resolutions, if you're source content is 720p, then you can make multiple compressed versions from that source file to test on tablets and see where that "sweet spot" is between file size and text readability. – Danny F. Oct 22 '14 at 14:21
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Full HD (i.e. 1920x1080) should definitely be your standard. It is a current standard now for movies, TV shows, etc., lots of digital media is Full HD. It will offer a better viewing experience on high-resolution tablets (e.g. Retina iPads) which have almost double that resolution. The file sizes as you said most likely won't be an issue with MP4 and H.264 codec which can compress 1080p video very small. Any device made after 2005 can play 1080p without problems, and the OSes of the tablet will automatically downscale if needed. Full HD is a very popular standard and sometimes required for certain purposes. Full HD will also offer clear footage of the instructor at the beginning with no blurriness. I often find blurry videos to be often a sign of low-quality work. In addition, using compression techniques like MP4 will create visual artifacts (little blocks of random color) which when upscaled from a low resolution become more prominent, thus being annoying and distracting; 1080p will not completely eliminate those artifacts but it will not upscale as much and the artifacts will be much smaller.

Also it's a nice marketing scheme to slap "FULL HD!!!" on your ads.

  • I agree with your marketing idea ;-) – plocks Oct 22 '14 at 7:47

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