user21476: I want to encode many little 10s-videos in 720p. As I want to play them in a big matrix (6 by 6 videos) in chrome, I am wondering what codec / encoding to use so that the stress on my cpu/gpu is as low as possible when playing them back. I want playback to be as smooth as possible. I don't care for the specific format, audio or filesize.
4 by 4 plays back fine but at 6 by 6 it becomes a bit stuttering.

user1950: I'd say your encoding settings are going to be more crucial, given you're limited to the codecs that Chrome can play. Unless I'm wrong you can only use MP4 / h.264 and WebM / VP8 unless you install plugins. 
Try lowering the profile of your mp4, e.g. encode using baseline profile. That will mean less compression–so larger files for the same quality or lower quality at the same size–but it reduces the processing power needed to display it.
It is worth noting that there are more hardware decoders commonly available for h.264 encoded video than there are for vp8, meaning that it's more likely to be handled at the hardware level than vp8.

21476: <p>I want to encode many little 10s-videos in 720p. As I want to play them in a big matrix (6 by 6 videos) in chrome, I am wondering what codec / encoding to use so that the stress on my cpu/gpu is as low as possible when playing them back. I want playback to be as smooth as possible. I don't care for the specific format, audio or filesize.</p>

<p>4 by 4 plays back fine but at 6 by 6 it becomes a bit stuttering.</p>
 1950: <p>I'd say your encoding <em>settings</em> are going to be more crucial, given you're limited to the codecs that Chrome can play. Unless I'm wrong <a href="https://developers.google.com/cast/docs/media" rel="nofollow noreferrer">you can only use</a> MP4 / h.264 and WebM / VP8 unless you install plugins. </p>

<p>Try lowering the <a href="http://blog.mediacoderhq.com/h264-profiles-and-levels/" rel="nofollow noreferrer">profile</a> of your mp4, e.g. encode using baseline profile. That will mean less compression–so larger files for the same quality or lower quality at the same size–but it reduces the processing power needed to display it.</p>

<p>It is worth noting that there are more <a href="https://en.wikipedia.org/wiki/H.264/MPEG-4_AVC_products_and_implementations#Decoding" rel="nofollow noreferrer">hardware decoders</a> commonly available for h.264 encoded video than there are for <a href="https://en.wikipedia.org/wiki/VP8#Decoding" rel="nofollow noreferrer">vp8</a>, meaning that it's more likely to be handled at the hardware level than vp8.</p>
