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Shortly before the start of SMPTE 2017 Technical Conference & Exhibition, TV Technology spoke with Thierry Fautier, vice president of video strategy, Harmonic, about his Thursday session “State-of-the-Art Virtual Reality Streaming: Solutions for Reducing Bandwidth & Improving Video Quality.”
TV TECHNOLOGY: Tiling seems like an interesting solution to the bandwidth problem VR streaming faces. Could you describe the problem and how VR tiling offers a solution?
THIERRY FAUTIER: First let us look at the limitations of a classical system, where a 4K video is sent to an HMD after stitching and only 1/10 can be watched and therefore creates a fuzziness effect on HMD.
Tiling is solving two problems:
· Increases the resolution of VR video as the sent video is the native resolution of the HMD, vs. 1/10 is watched in classical method
· Decreases the bitrate of the transmitted video, as only the viewport of the watched video is sent, resulting in a saving of up to 80 percent, we have measured 50-75 percent in our experiments
We show the system diagram of a tiling system to HMD.
TVT: How can tiling anticipate which way a VR viewer will look in order to make sure the correct image information is present to enable a seamless experience?
FAUTIER: There areltiple techniques used: mu
· First, the full viewport video is sent in lower resolution in case the tiles are not refreshed instantly
· Second, the client can request a larger window than the one watched (pre fetch)
· Last, we can do some prediction of where the user will move it head next, this works well for Live video. Of course for VoD we can also build analytics.
TVT: Is VR tiling strictly a solution for head-mounted displays, or is it appropriate for tablet and smartphone use regardless is whether the device is swiped or used in magic window mode?
FAUTIER: At IBC, we were showing how tiling is used on a tablet. The same principle applies vs HMD for any 2D device (phone, tablet, PC, TV, etc.)
We show the system diagram of a tiling system to 2D device.
TVT: What about 4K and 8K VR? Do these present a more difficult challenge for VR tiling given the larger amount of data required?
FAUTIER: There are two approaches:
· By saving, in that case we encode in tiling 4K, transmit HD and therefore get a similar quality as legacy at 50-75 percent bitrate saving
· Quality increase, in that case we encode in tiling 8K, transmit 4K and therefore get a much better quality than legacy same at the same bitrate
One very important aspect: 8K VR tiling works on legacy devices. This is a key feature of tiling.
See diagram and measurements.
