[BUG] S905X Krypton: Frame skips caused by burned-in forced subtitles

jd17 · May 7, 2017 at 6:08 PM

Blu-ray's original forced ~~burned-in~~ subtitles trigger massive frame skips.

Device type:
S905X
Build:
8.0.1j
Device:
Mini M8S II 2GB/16GB

How to reproduce:
Play sample file from Avatar (BD remux) and monitor PlayerDebug for frame skips.

Specs from sample video in log:

Quote

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 2 frames
Codec ID : V_MPEG4/ISO/AVC
Duration : 1 min 7 s
Bit rate : 22.4 Mb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (23976/1000) FPS
Original frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.451
Stream size : 180 MiB (84%)
Default : Yes
Forced : No

Audio
ID : 2
Format : DTS
Format/Info : Digital Theater Systems
Format profile : MA / Core
Mode : 16
Format settings, Endianness : Big
Codec ID : A_DTS
Duration : 1 min 7 s
Bit rate mode : Variable / Constant
Bit rate : 4 133 kb/s / 1 509 kb/s
Channel(s) : 6 channels
Channel positions : Front: L C R, Side: L R, LFE
Sampling rate : 48.0 kHz
Frame rate : 93.750 FPS (512 spf)
Bit depth : 24 bits
Compression mode : Lossless / Lossy
Stream size : 33.3 MiB (16%)
Language : English
Default : Yes
Forced : No

Display More

Support logs:
Attached.
Every new subtitle line triggered one or two frame skips.
I think there also was one skipped frame in the beginning w/o subtitle (see other bug report).

**mmpp** · May 7, 2017 at 6:42 PM

Nitpick: These are not "burned in" subtitles, but "forced" ones - they are a separate stream, and get shown by default. "Burned in" is used when they are rendered and made part of the video stream during re-encoding.

I mentioned the same problem with a different sample here: thread-7559.html

I noticed that custom fonts / unicode characters make the frame drop more apparent. Then again, some super-heavy subtitles with effects and whatnot get rendered just fine. It is a different format (substation alpha, or "ssa") so the reason for the problem here and in my sample might lie in something that is specific to blu-ray subtitles (pgs format, I think)

**kszaq** · May 7, 2017 at 7:25 PM

jd17 Thank you for providing sample and Kodi log. mmpp I must have missed that report of yours, I'm a busy man recently...

I have tested the file and can confirm the issue... and that it's also present when using Kodi on Windows, definitely not Amlogic-specific issue! I will see if I can escalate this. If you can reproduce on Windows, you might also want to post a bug report on Kodi forum: Kodi Community Forum - Video Support

jd17 · May 7, 2017 at 7:26 PM

Quote from mmpp

Nitpick: These are not "burned in" subtitles, but "forced" ones - they are a separate stream, and get shown by default. "Burned in" is used when they are rendered and made part of the video stream during re-encoding.

OK I understand. I thought it was burned in because there was no way to deactivate the subtitle, but I guess that is kind to the intention of "forced".

Quote

I mentioned the same problem with a different sample here: thread-7559.html

Sorry I missed that - I hope that is not an issue?

Quote

I noticed that custom fonts / unicode characters make the frame drop more apparent. Then again, some super-heavy subtitles with effects and whatnot get rendered just fine. It is a different format (substation alpha, or "ssa") so the reason for the problem here and in my sample might lie in something that is specific to blu-ray subtitles (pgs format, I think)

Yes, PGS is correct - which is a picture based subtitle type.
SSA/ASS and SRT are text-based as far as I know.
[hr]

Quote from kszaq

I have tested the file and can confirm the issue... and that it's also present when using Kodi on Windows, definitely not Amlogic-specific issue! I will see if I can escalate this. If you can reproduce on Windows, you might also want to post a bug report on Kodi forum: Kodi Community Forum - Video Support

I cannot reproduce the issue in Windows.
However, I am using a Leia Alpha in Windows, so it might already be known/fixed in Kodi.
(Kodi 18.0 Alpha1 from 16 April 2017.)

**mmpp** · May 7, 2017 at 7:45 PM

jd17 it is not an issue, but an indication that the problem is not an isolated issue on your side

kszaq I cannt reproduce the frame drops with kodi 17.0 on windows 10 64bit with nvidia 960 and 4k monitor. ctrl-shift-o shows no frame drops and the video is visually smooth

**kszaq** · May 7, 2017 at 8:36 PM

My laptop is Windows 7 64-bit, i7-3720QM, Intel HD 4000 and the issue can be reproduced with latest stable Kodi.

**mmpp** · May 7, 2017 at 8:48 PM

My notebooks have intel graphics, I can try to reproduce there later this week.

jd17 · May 7, 2017 at 9:09 PM

My test with Leia was on an i5-7500 with Intel HD 630.
The monitor does not support 23.976fps though, so the video was played at 60fps.
Maybe this has an impact on the subtitle issue?

I will test this on RPi2 if I have the time.

minimoe · May 7, 2017 at 10:45 PM

On my lowly laptop (i3-5005U/Intel Graphics 5500/Win10 64bit/Kodi 17.1) and out of 4 plays, 2 were perfect and the other two dropped 2-3 frames long before the subtitles appeared. The subtitles didn't seem to cause frame drops.

With LE 8.0.1f there are dropped frames just before the subtitles for the alien language appear. These are actually "burned-in", the PGS subtitle stream in the sample is for the English dialogue only.

**kszaq** · May 7, 2017 at 11:03 PM

The subtitles aren't burnt-in, you can turn them off. I have played the sample several times on Windows and there's always a frame drop when the subtitle is shown.

minimoe · May 7, 2017 at 11:25 PM

Quote from kszaq

The subtitles aren't burnt-in, you can turn them off.

Well... I can't!
Even with subtitles disabled, the subtitles with the unusual font (the ones that cause the frame skips in LE) still appear.

You're right though, they are not burned-in. I remuxed the file without the subtitle stream and all the subtitles are gone.

jd17 · May 20, 2017 at 9:56 AM

Quote from jd17

I will test this on RPi2 if I have the time.

I finally had time to dig up the good old RPi2.
I can confirm that the skips occur on RPi2 as well (official LibreELEC 8.0.1).

This definitely makes this a global Krypton issue.

jd17 · May 22, 2017 at 9:30 AM

I was wondering if it is maybe possible to import the fix from a Leia Alpha?
As I said, I do not have these subtitle skips in my Leia Nightly build in Windows, I could also test a Leia Nightly for the Pi if that helps.

Unfortunately I don't know when and how it was fixed - maybe you (or someone) can make sense of the Leia Nightly history log?

**kszaq** · May 22, 2017 at 10:20 AM

There are ca. 1400 commits from Krypton to Leia. Unless the fix is something trivial it is very unlikely that it can be ported. Have you reported the bug to Kodi bugtracker/forum?

jd17 · May 22, 2017 at 10:32 AM

No, not yet.
I tried to search for "subtitle" and "skip" in the forums, because I wanted to make sure there is no report yet (judging from the issue apparently being fixed in Leia).
However, I did not find anything, so I will report it.

Can you give me a hint of where to report the bug?
Would "Video Support" be the correct subforum?
Kodi Community Forum - Video Support

jd17 · May 28, 2017 at 12:44 PM

Official bug report in the Kodi forum:
[BUG] Frame skips caused by forced subtitles