The crew on tech forum Geekzone have recently been wondering if Spark Sport has dropped its frame rate, making its video look worse on some devices.
One member, Richard Fewtrell, said: "It's not a popular move. I have an Apple TV 4 and the Spark Sport picture quality looks terrible."
The Herald asked Spark Sport to confirm or deny a lowered frame rate.
A spokeswoman confirmed the streaming services frame rate has been lowered but said it was to provide a smoother stream that would behave well on more devices.
Regardless, the move gives Sky Sport a bragging point as it prepares to relaunch its Fanpass app on August 14.
The upgraded Fanpass - which is being rebranded Sky Sport Now to reflect it and which will now carry all of the channels in the expanded Sky Sport lineup - will offer 50 frames per second (fps) video at 1080p HD (it's previously topped out at 720p).
"We did recently change the framerate from 50/60fps to 25/30fps," the Spark Sport spokeswoman said.
"This decision was taken to ensure that we were able to launch on a wide variety of devices and ensure accessibility to the Rugby World Cup in as many New Zealanders' homes as possible. While some devices were playing 50/60fps successfully, other devices wouldn't have performed well if we had launched them at 50/60fps.
"While this change has meant reduced quality for some customers, it has delivered service improvements for other customers, such as people with older laptops or Chromecast – their stream is much more stable at 25/30fps and delivers a better viewing experience."
Spark has promoted Google's Chromecast - a $69 widget for wirelessly streaming video from a laptop, tablet or smartphone to a TV - as one of the primary ways for viewing Spark Sport on a regular telly.
But only the latest Chromecast, which has been on the market for less than a year, supports a framerate of up to 60fps at the 1080p high-definition (HD) video offered by Spark Sport.
The first and second generation Chromecasts (first released in 2013 and 2015 respectively) only support up to 30fps at 1080p. (Sky says its Sky Sport Now app will automatically adjust its quality for older Chromecasts).
The Spark Sport spokeswoman added, "25/30fps is standard for most online sports providers - and all of the sporting content that we are showing on Spark Sport is only provided by the sporting body at 25/30fps. So we are not limiting the stream quality from what's being provided to us."
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She continued, "That said, we have noticed some minor changes to quality and we're actively looking at a variety of options for improving picture quality prior to the tournament starting. Frame rate is only one of a whole raft of technical levers that we can pull that affect the viewing experience across the wide range of devices that we support.
"Our aspiration to return to 50/60fps for some devices in future where it is compatible and improves image quality. However, this won't be feasible before the Rugby World Cup as we are focused on reducing operational complexity to ensure a great experience for all RWC viewers."
The frame rate debate comes just days before Spark Sport starts streaming the first games in the 2019/20 English Premier League season in what will be the platform's biggest test before the RWC.
Spark Sport is already offering preview content and pre-season friendlies on-demand. Lowered frame rate or not, the Herald has found the video quality on a par with HDTV, with the movement of the ball (a bugbear with previous EPL streamers) easy to follow.
In another safety-first measure, Spark earlier decided not to offer a Spark Sport stream in 4K or Ultra HD, which offers four times the picture quality of 1080p HD.
The company says 4K streaming is supported by its platform, however, and it will look at adding it in future.
Netflix and Amazon's Prime Video offer 4K, but local broadcasters and services do not.