# Video quality question **URL:** \ **Category:** General Discussions\ **Created:** [February 4, 2019, 2:46am UTC](https://forums.plex.tv/t/video-quality-question/371335 "2019-02-04T02:46:42Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Brodieman37](https://sea1.discourse-cdn.com/plex/user_avatar/forums.plex.tv/brodieman37/32/271974_2.png) [@Brodieman37](https://forums.plex.tv/u/Brodieman37)\ **Post date:** [February 4, 2019, 2:46am UTC](https://forums.plex.tv/t/video-quality-question/371335/1 "2019-02-04T02:46:42Z")
Starting to build a 4k library. Hoping to get some help with what to look for in a good quality 4k video. Example below, which is better? Why? They are the same movie, one is 15GB and one is 30GB. Why is one twice the size? Thanks for any advice! 15gb Format : HEVC Format/Info : High Efficiency Video Coding Format profile : Main 10@L5.1@High Codec ID : V\_MPEGH/ISO/HEVC Duration : 2 h 17 min Bit rate : 10.5 Mb/s Width : 3 840 pixels Height : 1 600 pixels Display aspect ratio : 2.40:1 Frame rate mode : Constant Frame rate : 23.976 (24000/1001) FPS Color space : YUV Chroma subsampling : 4:2:0 (Type 2) Bit depth : 10 bits Bits/(Pixel\*Frame) : 0.072 Stream size : 10.1 GiB (67%) 30gb Format : HEVC Format/Info : High Efficiency Video Coding Format profile : Main 10@L5.1@High Codec ID : V\_MPEGH/ISO/HEVC Duration : 2 h 17 min Bit rate : 24.4 Mb/s Width : 3 840 pixels Height : 1 612 pixels Display aspect ratio : 2.40:1 Frame rate mode : Constant Frame rate : 23.976 (24000/1001) FPS Color space : YUV Chroma subsampling : 4:2:0 Bit depth : 10 bits Bits/(Pixel\*Frame) : 0.165 Stream size : 23.4 GiB (77%) ---
**Author:** ![Dan\_123](https://sea1.discourse-cdn.com/plex/user_avatar/forums.plex.tv/dan_123/32/87738_2.png) [@Dan\_123](https://forums.plex.tv/u/Dan_123)\ **Post date:** [February 4, 2019, 11:06am UTC](https://forums.plex.tv/t/video-quality-question/371335/2 "2019-02-04T11:06:00Z")
All modern video compression is ‘lossy’, meaning that some amount of information (quality) is destroyed by compression. For all modern compression methods (in this case x.265 / HEVC) the amount of compression is adjustable as a trade-off between quality and encoding speed (and to a lesser extent CPU required to decode). So the quick answer is that the large file contains more information, so it’s higher quality - BUT the big caveat is that when compressing the video, the amount of CPU effort expended to compress the video matters. It’s possible to carefully analyze the video (at the expense of encode speed) and find a very efficient (small size) encoding with a very high quality, whereas if someone wants to shrink a file in a hurry, the CPU analysis isn’t as good so either the file is bigger or the quality is worse (or both). The only real answer is to watch them (at least a few scenes) and see if you can tell the difference. If you can’t see the difference the smaller is fine, sometimes it will even be better quality to your eyes. If you’ve got the HDD space, just store the video streams without re-encoding them, the quality will never improve by re-compressing. (Blu-ray are mostly x.264/AVC native and UHD is x.265/HEVC, with exceptions). Also, a movie is more than video, it’s also audio. Pay attention to the audio quality, especially to extra audio-tracks. If you don’t want all the languages, they just take up space. ---
**Author:** ![Brodieman37](https://sea1.discourse-cdn.com/plex/user_avatar/forums.plex.tv/brodieman37/32/271974_2.png) [@Brodieman37](https://forums.plex.tv/u/Brodieman37)\ **Post date:** [February 4, 2019, 1:52pm UTC](https://forums.plex.tv/t/video-quality-question/371335/3 "2019-02-04T13:52:32Z")
Thanks for the tips. I’ll give each a watch. I wasn’t sure if there was somethings in the stats that tells you “This one is way better because of this”. ---
**Author:** ![Dan\_123](https://sea1.discourse-cdn.com/plex/user_avatar/forums.plex.tv/dan_123/32/87738_2.png) [@Dan\_123](https://forums.plex.tv/u/Dan_123)\ **Post date:** [February 5, 2019, 2:17pm UTC](https://forums.plex.tv/t/video-quality-question/371335/4 "2019-02-05T14:17:35Z")
Visual quality is highly subjective, so no easy stat can tell you quality, but given the choice between two well-done encodes the higher the bitrate (large size) generally means higher quality. Remember though, that you can turn the bit-rate up but not get good quality, especially if you start with poor source material. If you encode, then re-encode, it’s like a photocopy of a copy, each time it gets worse, and nothing can make a source better than it was (for example, you’ll never turn a DVD into a 4k UHD). Also, Codec does make a big difference. In your example they were both the same format and codec (x.265/HEVC), but if they’d been different that could be a tell toward quality. MPEG-2 (DVD format) is not very efficient (large files) but is very easy on the CPU, it was made when embedded CPUs for DVD players had minimal processing power. x.264 (AVC) was a big jump in efficiency, but requires more CPU power to encode and play-back. Nowadays most any CPU can handle it, but real-time transcoding on an embedded device (like a NAS) is problematic. But as an example, an MPEG-2 DVD is around 4-5 GB, whereas the same video at roughly the same quality is only around 1 GB when encoded with x.264. The same is true again for the new x.265. Even a decent modern processor will be pressed to do real-time transcoding of x.265 source material, especially 4k, but the advantage is smaller files - typically only about half the file size is needed to achieve similar quality to x.264. ---
**Author:** ![AmazingRando24](https://sea1.discourse-cdn.com/plex/user_avatar/forums.plex.tv/amazingrando24/32/351517_2.png) [@AmazingRando24](https://forums.plex.tv/u/AmazingRando24)\ **Post date:** [February 5, 2019, 2:21pm UTC](https://forums.plex.tv/t/video-quality-question/371335/5 "2019-02-05T14:21:10Z")
> [@Dan\_123](#): > > Visual quality is highly subjective The biggest truth in the Plex forum. ---
**Author:** ![Brodieman37](https://sea1.discourse-cdn.com/plex/user_avatar/forums.plex.tv/brodieman37/32/271974_2.png) [@Brodieman37](https://forums.plex.tv/u/Brodieman37)\ **Post date:** [February 5, 2019, 5:20pm UTC](https://forums.plex.tv/t/video-quality-question/371335/6 "2019-02-05T17:20:48Z")
Thanks again Dan! ---
**Author:** ![system](https://global.discourse-cdn.com/plex/original/3X/2/a/2acb9765406f63293d357b4ec509ec39aa28f2ad.png) [@system](https://forums.plex.tv/u/system)\ **Post date:** [May 6, 2019, 5:20pm UTC](https://forums.plex.tv/t/video-quality-question/371335/7 "2019-05-06T17:20:51Z")
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