Why a 4K portrait signage player shows a quarter of the layout

Why does only a quarter of the layout appear on a 4K portrait screen?

The signage app is drawing a 2160 x 3840 window into an internal graphics buffer of only 1080 x 1920. The panel can only receive the buffer's top-left corner: 2,073,600 of the 8,294,400 pixels the layout asks for.

A 4K-rated Android box does two separate jobs. The render buffer is the surface the signage app actually draws into. The output stage takes that surface and sends a signal down the HDMI cable. An HDMI 2.0 output carries a 3840 x 2160 signal at 60 Hz even when the buffer behind it is 1080p. Plenty of 4K-rated boxes work this way: they render at Full HD and let the output stage scale the picture up to the panel.

The quarter appears when a screen-dimensions override, an entry such as 0,0,2160,3840 in the player app's display settings, forces the layout window to the panel's full size. The layout is then twice as wide and twice as tall as the buffer (2160 / 1080 = 2, 3840 / 1920 = 2), and everything outside the buffer never reaches the panel. What is left is the top-left quadrant: 1080 x 1920 of 2160 x 3840, one quarter of the area. The files are innocent. A 4K PNG and a 4K H.264 clip fail the same way because the window, not the file, is oversize.

The basics of why a 4K-rated player ends up rendering at 1080p are in why your 4K signage player only renders at 1080p.

How do you tell a real 4K player from one that upscales?

Set the player's HDMI output to 4K, then read the resolution line on the signage app's status screen: 1080 x 1920 there means the box renders Full HD internally and scales the picture up on the way out.

Two numbers decide, and they live in two places. The output setting controls the signal: HDMI 2.0 carries 3840 x 2160 at 60 Hz to the panel. The status screen reports the surface the app renders into, and that is the number the content has to match. If the output reads 4K and the status line reads 1080 x 1920, the box upscales a Full HD render. No CMS setting, cable swap or TV menu change makes that buffer bigger. The device is the limit.

The status screen carries one more useful line here: which rendering method the app is using. Note it when video misbehaves in other ways; for this fault the resolution line decides.

Which symptom points to which cause?

Read what is missing: a missing three quarters points to a window forced past the buffer, a complete but soft picture points to an upscaled 1080p render, and stutter or refusal to play points to frame rate or codec.

• Top-left quarter of the layout, the rest black. A window forced past the buffer. Compare the screen-dimensions override in the app's display settings with the resolution on the status screen.
• A complete picture that looks softer than the panel should. The buffer is 1080 x 1920 and the output is scaling it up; nothing is clipped. Play a 1080 x 1920 layout: it should fill the panel and look right.
• 1080p layouts perfect in portrait and landscape, 4K layouts wrong in both. That is the buffer limit, and the cable and the TV are fine.
• 4K images fine, 4K video stuttering, dropping frames or refusing to start. Frame rate or codec. Read the file's frame rate first; 60 fps is the usual offender.
• Switching the app's rendering method changes nothing. The window was oversize, so the renderer was never the problem; remove the forced dimensions instead.

What is the fix?

Remove the forced screen dimensions, leave the HDMI output at 4K, and let the signage app detect the screen size; then build every layout at the resolution the status screen reports.

1. Delete the screen-dimensions override. The entry forcing 0,0,2160,3840 is what creates the quarter; with it gone, the app sizes its window from the buffer again.
2. Leave the player's HDMI output at 4K (3840 x 2160) so the panel receives a native 4K signal.
3. Restart the app, which is designed to bring the show back up full screen within seconds, then read the status screen. A 1080 x 1920 report on a box outputting 4K means the device is the ceiling, and no server-side setting raises it.
4. Build layouts at the reported resolution. The worked example below shows what a 1080 x 1920 buffer delivers on a 43-inch portrait panel.
5. Re-export any 4K video at 30 fps or below and test that file on the real player before the screen is mounted; testing video bitrate for a signage player before you deploy is the test routine to copy.

With the override gone, every layout pixel is drawn and the scaling happens after rendering, in the output stage where it belongs. A switch of the app's rendering method changes nothing here: the window, not the renderer, is oversize.

Recommendation: Keep the HDMI output at 4K, delete any forced screen dimensions, and build content at the resolution the status screen reports: 1080 x 1920 layouts on an upscaling Android box, with H.264 video capped at 30 fps. Chase 2160 x 3840 layouts only on a player whose status screen reports that buffer, and only for viewers standing close enough to need it.

Why should 4K video stay at or below 30 fps?

Halving the frame rate halves the decoder's pixel rate: 3840 x 2160 at 60 fps is 497 million pixels per second, at 30 fps it is 249 million. The working guidance for Android players is 30 fps or below.

The arithmetic: one 4K frame is 8,294,400 pixels, so 60 fps asks the decoder for 497,664,000 pixels per second and 30 fps asks for 248,832,000. At 1080p the same box handles 2,073,600 x 60 = 124,416,000 pixels per second. That is why a Full HD clip plays smoothly on a box that chokes on the same content at 4K. H.264 is the export codec to keep; H.265 and VP9 decode only where the box supports them, so a file that plays on one player can fail on another. If stutter survives a 30 fps re-export, fixing video that stutters on a 4K monitor but not on 1080p walks the next checks. The bandwidth and codec side of machine video has its own page at industrial machine video streaming codecs, bandwidth and players.

Worked example: what does a 1080 x 1920 buffer deliver on a 43-inch portrait TV?

On a 43-inch 4K panel fed from a 1080 x 1920 buffer, content pixels land at about 51 per inch. Capitals 20 pixels tall, about 0.4 in, read comfortably from 8 ft.

Work the chain:

• Pixel density. A 43-inch panel at 3840 x 2160 has √(3840² + 2160²) = 4406 pixels across the diagonal, so 4406 / 43 = 102.5 pixels per inch.
• Panel size in portrait. 2160 / 102.5 = 21.1 in wide, 3840 / 102.5 = 37.5 in tall.
• Content density. The 1080 x 1920 buffer is stretched 2x to fill the panel, so content pixels land at 1080 / 21.1 = about 51 per inch.
• Letter height for the distance. The planning figure of 20 ft of viewing distance per inch of capital height for fast reading gives 8 / 20 = 0.4 in capitals for a viewer at 8 ft; the FHWA figure of 30 ft per inch puts those same 0.4 in capitals out to 0.4 x 30 = 12 ft.
• In content pixels. 0.4 in x 51 pixels per inch = about 20 pixels of capital height, with line spacing at 1.7 x 20 = 34 pixels.

Result: a 1080 x 1920 layout with 20-pixel capitals and 34-pixel line spacing reads from 8 ft and holds to 12 ft on this panel. The 2160 x 3840 layout you were fighting for halves the content pixel size in each direction, which matters to a reader at 3 ft and to nobody at lobby distance.

What content resolution should you build for a portrait screen?

Build at the resolution the status screen reports, not the one printed on the TV datasheet: 1080 x 1920 for an upscaling box, 2160 x 3840 only when the status screen itself reports it, and H.264 video at 30 fps or less.

• Export stills at the buffer resolution exactly. A 2160 x 3840 PNG on a 1080 x 1920 buffer is four times the pixels for no gain on an upscaling box; a 1080 x 1920 PNG on a true 4K buffer gives up half the sharpness in each direction.
• Check the layout fits before export: checking portrait signage layout fit on a screen gives the fit routine.
• Build images portrait-native: preparing portrait signage images for a mounted screen covers sizing and crops.
• If the player fights rotation as well as resolution, when a signage player lacks portrait rotation support is the next stop.

An all-in-one portrait display that runs its own player skips the external box, so buffer and panel are one matched system; the panel-mount display range is built that way, the screen size guide sizes the panel to the wall before any of this matters, and the digital signage player guide covers how offline playback behaves once the resolution question is settled.

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