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H.265 videos with PGS subtitles are buffering in Web Player

greentrancergreentrancer Posts: 34Members ✭✭
edited February 12 in QNAP

Hello,

As the title says, I think that I came across a bug or limited functionality.

Most of my TV episodes and movies are in H.265 (8 and 10 bit) and some of them came with PGS subtitles. Whenever I play those files via the Web Player in Chrome, Firefox, Edge, Chrome on Android, etc., the video plays for about 30 seconds, then it buffers for 5-10, and this process repeats for the entire duration. I do not have similar problem with SRT subtitles. Does anyone know a way around this, or if anyone else is experiencing the same problem?

I have a QNAP TS-453mini and the CPU is around 30% when transcoding a video (10bit) as described above, and the usage does not significantly change when the buffering occurs.

Thank you.

Best Answers

Answers

  • greentrancergreentrancer Posts: 34Members ✭✭

    Thank you very much for the explanation, that kind of makes sense.

    I was not aware that subtitle transcoding is single core. The CPU usage is around 26-27% (I just rounded it up to 30), but still, that goes over 25%, so yeah, that might the case unfortunately...

    Any other opinions are also welcome.

  • trudgetrudge Posts: 2,279Members, Plex Pass Plex Pass
    edited February 12

    @greentrancer said:
    I was not aware that subtitle transcoding is single core. The CPU usage is around 26-27% (I just rounded it up to 30), but still, that goes over 25%, so yeah, that might the case unfortunately...

    Well yeah, you've got a 2.0Ghz CPU that can jump up to 2.42 with turbo on a single core so you'll never see exactly 25.

  • greentrancergreentrancer Posts: 34Members ✭✭

    Okay, so I have done the following:

    • got a SRT subtitle for the same episode and it plays perfect with that - the buffer seems to be always 5% ahead (seeing that on PlexPy) without almost any use of CPU

    • when I switch to PGS, it buffers again about 5% ahead, but then it stops and/or slows down a lot, hence the video reaches the buffers and it pauses

    My concern is how can a PGS subtitle slow down so much the episode, when a SRT has not the slightest issue? This seems more like a Media Server performance issue than CPU not being able to handle it... Or am I missing something here? Thank you.

  • trudgetrudge Posts: 2,279Members, Plex Pass Plex Pass
    edited February 12

    PGS needs to transcode so they are burnt into the stream as the browser cannot handle them client side. aka, you server has lots of work to do.

    SRT does not need to transcode as they can be handled by the browser client side. aka, you server needs to do very little, just sent the file and subs.

    PGS are images, SRT is text. Text is simple to overlay.

  • greentrancergreentrancer Posts: 34Members ✭✭

    I know and understand that, however it seems that some 'static' images that appear here and there require too much processing power? With SRT, the CPU sometimes goes down to 7% from about 23% (I guess when it finishes transcoding 5% ahead), and the average after that is around 16%.

    I know that transcoding a H.265 10bit require quite a bit of power, but a simple image based subtitle does not justify another 10% CPU use on top, plus streaming buffering...

    Does this seem normal to others? Hmm...

  • greentrancergreentrancer Posts: 34Members ✭✭

    I understand, thank you all for the clarifications!

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