HDX is a hi-definition (HD) format developed by Vudu that allows streaming video at a better quality than HD streams from other providers like Amazon Instant Video, Google Play and iTunes. HDX video is streamed at 1080p and 24 frames per second. While Amazon, Google, Apple and Vudu HD all deliver HD streams at 1080p resolution, HDX offers better video quality because:
- HDX encodes video at a higher bitrate (almost twice that of the HD version) – on average around 9.5 Mbps, and as high as 20 Mbps for complex scenes.
- HDX preserves a film's native 24 frames per second
- HDX uses 5.1 Dolby Digital Plus Surround Sound for audio
- HDX uses TruFilm, a set of Vudu's proprietary video encoding techniques that use the H.264 standard but optimizes for subjective video quality and minimizing compression artifacts by using techniques such as:
- Psychovisual Processing: Certain types of scenes — e.g., dark skies, water bodies, fast action —are more prone to pixelation and compression artifacting. HDX uses algorithms to detect such scenes and re-encode them so that the video quality that humans perceive is higher.
- Variable Bitrates: Not all scenes in a film contain the same level of detail, animation or motion. HDX uses a higher bitrate — as high as 20Mbit/s — for scenes with a high level of detail and high motion/fast action segments of the film. Slower sequences use bit rates as low as 2 Mbit/s. This process of using variable bit rates allows for the highest possible video quality streaming over a broadband Internet connection.
- Color Gradient Processing: An algorithmic approach for tuning the picture — which may have been encoded for older CRT televisions — for best results on modern LCD and plasma television displays.
Caveats and Disadvantages
The biggest disadvantage of HDX is the amount of time it takes to download a full-length movie, if downloading it as opposed to streaming. For streaming, a fast broadband Internet connection is required, with bandwidth of over 4.5mbps for HDX, and over 2.25mbps for regular HD. Vudu offers a speed test page where users can check their Internet connection bandwidth, which can vary by day of week and time of day.
Another caveat is device capabilities. If your TV is only capable of 720p, or if the display cannot handle 24 frames per second, then you will not notice any difference in quality between the HDX and HD versions of the same video. If your display can't accept 1080p/24 at all, you may have to choose the 1080i output instead.
Vudu's FAQ page also lists bandwidth and system requirements to watch videos in HD and HDX.
HDX vs UHD
Vudu also offers a UHD — aka Ultra HD or 4K — format that offers even better video quality, a much higher resolution (to the order of 4,000 pixels), Dolby Vision (basically Dolby's version of HDR), and commercial theater grade Dolby Atmos surround sound.
Some users have reported that there is no noticeable difference in the video quality of UHD vs. HDX on Vudu streams. However, that is because not all devices are capable of streaming Vudu's UHD content. This infographic shows what devices currently support Dolby Vision (for video) and Dolby Atmos (for audio), and are therefore capable of playing 4K UHD content from Vudu.
- Demystifying Online Movie Rentals - Wall Street Journal
- Vudu's HDX upgrade delivers the best downloadable video quality to date - CNet
- Vudu’s New HDX Format Offers 1080p/24 Video with ‘Virtually No Artifacts’ - CEPro
- VUDU's HDX titles compare to Blu-ray's picture quality - Engadget
- FAQ on Vudu
- Streaming video quality comparison of Vudu HDX vs. Amazon HD vs. Hulu Plus - YouTube