Subtitles and NVDEC?

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mtbdrew
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Subtitles and NVDEC?

Post by mtbdrew »

I know when V31 first released there was a note regarding subtitles not work with NVDEC but is this issue still active or are subtitles supposed to be working now?
I'm running on Ubuntu 20.04 on both my backend and main remote frontend. Latest updates are installed for OS and Mythtv. Subtitles work for VDPAU as well as the other profile Codecs just not NVDEC.
wesnewell
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Re: Subtitles and NVDEC?

Post by wesnewell »

Never had a problem here.
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kmdewaal
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Re: Subtitles and NVDEC?

Post by kmdewaal »

I just did a quick test playing back recordings with MythTV master on Ubuntu 18.
DVB subtitles are shown both with VDPAU and NVDEC.
However, ATSC CC subtitles are shown with VDPAU but NOT with NVDEC.
wesnewell
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Re: Subtitles and NVDEC?

Post by wesnewell »

Both atsc and vbi work here on latest V31.
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mtbdrew
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Re: Subtitles and NVDEC?

Post by mtbdrew »

ATSC CC subtitles are shown with VDPAU but NOT with NVDEC is what I see here. Those who have theirs working, can you post your playback profile settings?

Thanks
Andrew
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Re: Subtitles and NVDEC?

Post by wesnewell »

I've got 5 frontends and they all use the same settings, which are pretty much the default ones for NVDEC Normal. All systems are xubuntu 20.04 LTS consisting of system in listed in sig line.
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pgbennett
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Re: Subtitles and NVDEC?

Post by pgbennett »

USA broadcast shows have cea-608 subtitles and they do not display with NVDEC. I just confirmed this by testing. The menu does not even show the subtitle option.

I suspect that the person who sees the subtitles is not really using NVDEC. Use "playback data" to see which decode method is being used. If you select NVDEC on a system that doesn't support NVDEC, it silently falls back to software decode and this may be what is happening.
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Re: Subtitles and NVDEC?

Post by wesnewell »

Here are my settings
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pgbennett
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Re: Subtitles and NVDEC?

Post by pgbennett »

You need to look at the playback data
While playing : Menu -> Playback -> Playback Data
The codec / dec will tell you whether it is using NVDEC
Screenshot_2021-05-28_16-47-11_resize.png
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Bigger image : https://www.dropbox.com/s/804ezfjevrvy0 ... 1.png?dl=0
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kmdewaal
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Re: Subtitles and NVDEC?

Post by kmdewaal »

Yes, this does select NVDEC but only if it is available for your graphics card. As far as I know NVDEC only works for Nvidia cards.
If you select NVDEC on e.g. Intel-only cards where NVDEC is not available then automatically FFmpeg is used instead.
CC subtitle playback with FFMpeg is OK.

The decoder that is actually used can be viewed when playing back by:
- Press "M" for the "Playback Menu" menu,
- 4th choice "Playback" for the "Playback" menu
- 4th menu choice "Playback Data"
then a black OSD appears with all kind of debug data. Second column, second entry is "Codec/Dec" and this shows on my Intel laptop "MPEG2 ffmpeg" even when NVDEC is selected. See picture below.
Screenshot from 2021-05-28 23-23-19.png
Screenshot from 2021-05-28 23-23-19.png (207.28 KiB) Viewed 14908 times
mtbdrew
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Re: Subtitles and NVDEC?

Post by mtbdrew »

pgbennett wrote:
Fri May 28, 2021 2:07 pm
USA broadcast shows have cea-608 subtitles and they do not display with NVDEC. I just confirmed this by testing. The menu does not even show the subtitle option.

I suspect that the person who sees the subtitles is not really using NVDEC. Use "playback data" to see which decode method is being used. If you select NVDEC on a system that doesn't support NVDEC, it silently falls back to software decode and this may be what is happening.
So any idea when this is or even if it is going to be supported with v31? I've heard that this is supposed to be the future codec for Nvidia cards but a none starter for those of use with hearing loss.
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kmdewaal
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Re: Subtitles and NVDEC?

Post by kmdewaal »

Now reported in Github issue #364 https://github.com/MythTV/mythtv/issues/364.
N.B. This does not guarantee a quick fix but it does raise the visibility of this bug and it reduces the likelihood of this bug being forgotten.....
mtbdrew
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Re: Subtitles and NVDEC?

Post by mtbdrew »

Thank you.
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pgbennett
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Re: Subtitles and NVDEC?

Post by pgbennett »

In the meantime there are workarounds - you can select VDPAU or Standard decode. Alternatively you can set up a post-recording job to extract subtitles into a file after recording so that the player will pick them up. This would not help with Live TV, since it would only extract the subtitles at the end of a recording.
mtbdrew
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Re: Subtitles and NVDEC?

Post by mtbdrew »

Ya been forced to stay on VDPAU so far.
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