Can transcode 140Mbps HEVC but not 45Mbps?

[TDA]

With the Nvidia Shield TV I can transcode this video smoothly:

But not that one that is similar and lower bitrate:

The latter one keeps buffering.
Any idea why?

[Achilles]

PGS subtitles?

[TDA]

There are PGS subtitles on the one that struggles, indeed!
And it transcodes without buffering if I turn them off.

There are external SRT subtitles as well, so I thought it would play better with these ones but it also struggles.
I am supposed to burn only the image subtitles (as per the settings).
Any idea why it also fails transcoding smoothly with SRT subtitles?

[FordGuy61]

Burning subtitles forces the video transcode to happen on the CPU, bypassing any hardware acceleration. The CPU in the Shield may not be powerful enough to transcode 4K video in real time, which would cause the video to buffer.

Reference: Limitations When Running Plex Media Server on NVIDIA SHIELD.

Regarding SRT subtitles:

Depending on the client, if the audio is transcoding, enabling any subtitle, including SRT, forces a video transcode (which will happen on the CPU).

From personal experience, this happens with Android TV clients, such as the Shield & Amazon FireTV, and some Smart TV clients, such as LG WebOS.

[TDA]

That’s right, it seems to burn the SRT subtitles and transcode from the CPU when I play it on the TV (from the Nvidia Shield TV, so Android TV), and it keeps buffering.

But it transcodes using HW when I play it on the Chromebook, and plays smoothly:

Hmmm, I would have thought the Nvidia Shield TV is more capable of rendering an external SRT on the “client” side (Android TV) than my cheap Chromebook… That’s a bit of a shame as the end result is that I can’t play that video smoothly on my TV with subtitles…

Edit: actually, when I tried again after trying on the Chromebook and while another video is being hw transcoded (1080p->720p to external network), it now direct plays the video and works smoothly on the TV:

I don’t understand what I am doing differently… it seems all good now…

Edit 2: I think that’s because I switched to audio AC3 5.1 instead of TrueHD, which can be direct play and doesn’t trigger the hw transcode of the video either!