Can't play file with AV1 encoding with Dolby vision if there are subtitles

I have some AV1 encoded files with Dolby Vision and I found a few issues on Z9X (firmware -- Beta version v1.0.86):

1. When there are any external ort internal subtitles are present, it will not play. I get a "can't play video" error. If I remove the subtitles, the file plays just fine using the DV engine.
   
   The subtitle type does not matter, they all trigger the same error.
   
   
2. When I set the display to "Auto", it does not switch over to DV engine for this type of file and the HDR does not engage.

The file plays back normally on my PC using VLC player, and on my Hisense TV in Dolby Vision.

Here is the mediainfo:
-----------------------------------------------------------------------------------------------------------------
Writing application : HandBrake 20240530063100-5bc9b5d7f-master 2024053101
Writing library : Lavf61.1.100

Video
ID : 1
Format : AV1
Format/Info : AOMedia Video 1
Format profile : Main@L5.0
HDR format : Dolby Vision, Version 1.0, Profile 10.1, dav1.10.08, BL+RPU, no metadata compression, HDR10 compatible / SMPTE ST 2086, Version HDR10, HDR10 compatible / SMPTE ST 2086, Version HDR10, HDR10 compatible
Codec ID : V_AV1
Duration : 2 h 1 min
Width : 3 840 pixels
Height : 1 600 pixels
Display aspect ratio : 2.40:1
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0 (Type 2)
Bit depth : 10 bits
Default : Yes
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0001 cd/m2, max: 1000 cd/m2
Maximum Content Light Level : 1000
MaxCLL_Original : 1000 cd/m2
Maximum Frame-Average Light Level : 905
MaxFALL_Original : 905 cd/m2

Audio
ID : 2
Format : MLP FBA 16-ch
Format/Info : Meridian Lossless Packing FBA with 16-channel presentation
Commercial name : Dolby TrueHD with Dolby Atmos
Codec ID : A_TRUEHD
Duration : 2 h 1 min
Bit rate mode : Variable
Maximum bit rate : 7 335 kb/s
Channel(s) : 8 channels
Channel layout : L R C LFE Ls Rs Lb Rb
Sampling rate : 48.0 kHz
Frame rate : 1 200.000 FPS (40 SPF)
Compression mode : Lossless
Title : Dolby THD Atmos 7.1
Language : English
Default : Yes
Forced : No
Number of dynamic objects : 15
Bed channel count : 1 channel
Bed channel configuration : LFE

 

I can see that Handbrake has been used to encode this to AV1 - has the RPU been converted to Profile 10 also?

 

I'm not 100% sure but I would assume so. The problem is the subtitles. The file plays fine if there are no subtitles.

The same video encoded in HEVC and DV profile 7 or 8 also plays fine with including subtitles.

Running an extra test as from a preview encode it seems that the problem only exist in MKV files. If the file is in MP4 format it works fine.

 

I would assume the opposite if Handbrake has been used - I don't know of any public software that will encode correctly to Profile 10 (Handbrake supports 5-8).

If the file is not really Profile 10, but is, for example Profile 5 with an AV1 base layer, the VS10 engine is probably going to be buggy as hell and the subtitle issue may just be a symptom of that. It may not be of course, but a Dolby compliant P10 file would be needed to assess that before it's presented to the devs.

(By the way, I know MediaInfo reports Profile 10, but MediaInfo has a habit of making a lot of inaccurate assumptions and my guess would be it makes an assumption of Profile 10.1 if it sees an AV1 encoded base layer - I don't think it parses the RPU).

There seem to be a lot of people buggering about with AV1 & Dolby Vision at the moment, but so far I haven't seen anybody get it right.

 

You are right. Zidoo reports the file as Profile 5.

 

That seems to be happening a lot - people taking a Profile 5 or 8 HEVC file, encoding to AV1 but ignoring the RPU.

To be honest, I'm not really sure why, and Profile 5 is a very poor choice to attempt because it uses an entirely different colour space (IPT) so is bound to confound a Dolby decoder if encoded to AV1.

 

Here is the info from Zidoo.

VideoCount 1
AudioCount 1
FileExtension mkv
Format Matroska
FileSize 28.00G
FrameRate 23.976 FPS

VIDEO:
Format AV1
Format Level 5.0
HDR Format Dolby Vision / SMPTE ST 2086
HDR Format Profile 0A.0A
HDR Format Level 08
HDR Format Settings BL+RPU
HDR Format Combability HDR10 / HDR10
Duration 02:01:49
Width 3840
Height 1600
FrameRate 23.976
ColorSpace YUV
BitDepth 10
Title UHD
colour primates BT2020

AUDIO:
Format MLP FBA
Format Commercial If Any Dolby TrueHD with Dolby Atmos
CodecID A_TRUEHD
Duration 02:01:49
Channels 8
SamplingRate 48 KHz
Title Dolby THD Atmos
Language en
Default Yes

SUBTITLE:
ID 3
Format ASS
Language en
Default No
Forced No

The funny thing is, that everything seems to work fine when there are no subtitles (either in the MKV file or externally)

 

"HDR Format Profile 0A.0A" indicates Profile 10 - this is because it's an older version of MediaInfo being used which was recently updated to report Profile 10 as dav.1.10.

But as I've said elsewhere, MediaInfo tends to make assumptions when it can't make an empirical decision and that seems to be the case here.

Both versions of MediaInfo above report the Level (for DV you have a Profile defining the flavour of DV and a Level defining pixel rate) as "8". That would make the frame rate 48Hz - the level for 4K23 should be 6.

As I say, there'e no point approaching the devs with any Profile 10 issues (if there are any) unless a properly compliant file is tested. Such homebrew files should just be viewed as unsupported and as I say this subtitle issue is probably just a symptom.

I haven't seen any commercial Profile 10 files anywhere, as as I say, current public tools don't support it, so unless you have access to licenced Dolby software, as far as I know, it's not possible to produce it.