It seems both vdpau and nvdec are broken for Mpeg2 video. Particularly video that is 1080i, deinterlaced or not. I see blocking artifacts that are not present with VA-API or software decoding. This is reproducible in mpv and mythtv, but essentially anything that uses ffmpeg. I have generated a VDPAU trace but the partner sftp site doesn’t seem to work with blank credentials like this forums claims it does.
More info:
opened 02:27AM - 11 Sep 22 UTC
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* **Platform**: ```Linux mythtvbox 5.17.5-gentoo #1 SMP PREEMPT Sun May 1 02:28:31 EDT 2022 x86_64 Intel(R) Core(TM)2 Quad CPU Q9650 @ 3.00GHz GenuineIntel GNU/Linux```
* **MythTV version**: fixes/32
* **Package version**:
* **Component**: mythfrontend / mythavcodec
### What steps will reproduce the bug?
Playback 1080i video from OTA MPEG-TS with nvdec or VDPAU decoding.
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### How often does it reproduce? Is there a required condition?
Somewhat random but most often occurs during sharp scene transitions or high motion
### What is the expected behaviour?
No blocking artifacts
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Here's the "debug" playback output when this issue occurs:
https://pastebin.com/m6cfem9q
Here's a screenshot:
### What do you see instead?
Blocking artifacts
### Additional information
This issue I believe to be inherited during a resync to ffmpeg 4.4 but it's hard to say for certain. I _only_ exhibit this with VDPAU or nvdec decoding and the issue seems to disappear when the video is pulled from the transport stream into a regular mpeg2 container. I was able to see this same buggy behavior with nvdec on a different machine with mpv for a while, but now that I've updated ffmpeg and mpv over the past year or so, I cannot observe it anymore. The issue cropped up right around the v32 update and I seem to not be the only one exhibiting this issue, as this mailing list user also seems to have the symptoms: https://lists.archive.carbon60.com/mythtv/dev/638570
I'm attaching a minimally sized ts that exhibits the issue. Hopefully it's not too large.
[problem.zip](https://github.com/MythTV/mythtv/files/9541664/problem.zip)
I've mentioned this issue in issue #428. The machine using nvdec with mpv is leveraging ffmpeg 4.4.2, so it's at least fixed in that verison.
Let me know if there's anything more I can provide.