MythTV Official Community Forum

Hi,

I'm experiencing a slight studder when I use the TrueHD 7.1 audio track. I have a 7.1 Yamaha RX-V3900 receiver that recognizes the stream and is able to play it, but it's as if the video has a slight slowdown every second or so. It's very slight and I don't sense the slowdown in the audio, it's more visual. I can change to the 5.1 audio track in videos and then the studder is gone. This happens with all videos that have TrueHD 7.1 audio track.

I use MakeMKV to rip the BluRay's to .mkv video files. I have an i7 CPU and a GeForce GT 730 that is capable of TrueHD. I'm using the lated 30.0-Fixes branch but have noticed this studder for years. Could it be something as simple as my HDMI cable?

I'd be most appreciative If anyone has any suggestions that might help.

Thanks,
Vaska

I'm able to play the same video file using MPV without any studder, but my AV receiver shows PCM instead of TrueHD so I think I'm bitstreaming rather than asking the receiver to do the heavy lifting, unless I've got that backwards.

MPV plays the files fine with this command:

mpv -audio-spdif=truehd --aid=1 --alang=eng --audio-channels=8 file.mkv

Is there an equivalent way to bitstream with MythTV?

I have this same issue. In my case the studder is pretty significant and leads to an unwatchable movie. I posed about this on the mailing list but never got any significant feedback (looks like the pastebin I used for my log file has expired):

https://lists.gt.net/mythtv/users/626143

There is no studder when playing using VLC or other players, only with MythTV. It happened in both 30.0-fixes and now with 31.0-fixes. Switching the audio to 5.1 fixes the problem. No issues with other HD audio sources.

Neil

Thanks for the verification that it's not just me Neil. I guess the option to use an external player for videos exists but that comes with it's own drawbacks.

No problem Vaska!

Maybe with all the extra free time I have due to coronavirus seclusion I can generate new log files and see if we can get this fixed!

You are probably better asking on the dev mailing list about this.

You will likley have to supply a sample file and the more info you can give about your set up the better. The video playback has changed significantly in v31 so only do this if you can reproduce this in that version and please try the latest v31-fixes version available before reporting.

Will do, thanks Paulh. Any chance you could tell me what the syntax for launching the frontend with the required extra/verbose logging would be in order to hopefully observe/capture something helpful please?

I'm guessing 'mythfrontend --verbose playback' or maybe 'mythfrontend --verbose playback,audio' but I've asked the the question on IRC what the best options are. Just waiting for a reply from Mark K. who is the video player expert.

If someone can pull together a sample that is known to show the issue, I'll take a look - no promises though:) - if it's an audio issue, I'll likely draw a blank.

Other than that, is there a specific hardware configuration that triggers the problem? i.e. passthrough only

Regards
Mark

Sorry to have to ask this, but I'm having trouble creating a sample of a video with this problem. I'm trying to use dd to cut a section of a video. I'd like to skip to the middle where there is some action, but anytime I try to use skip= with the dd command the file becomes unplayable.

Also, where could I post a section of a video for review?

I would recommend you try cutting your video with ffmpeg using a syntax like this.

ffmpeg -ss 00:10:00 -i input.mp4 -to 00:12:00 -c copy output.mp4

-ss = start time
-to = finish time

For sharing, you might consider temporarily putting on google drive or dropbox and sharing unpublished link here.

You might also confirm you don't have a message like this in your mythfrontend log:

ALSA: Try to manually increase audio buffer with: echo 128 | sudo tee /proc/asound/card0/pcm0p/sub0/prealloc or something similar.

I suspect 7.1 audio might require a larger buffer and I believe mythtv will estimate the required buffer amount based on what you are playing back so check it when you start one of your 7.1 videos. The audio / video syncronization is baselined off the audio timestamps and jitter can occur even if you don't hear audible artifacts associated with buffer underruns.

I tried increasing the buffer all the way to 32000 and that didn't help. I also tried increasing logging in the frontend with "mythfrontend --verbose playback,audio" which shows this:

https://pastebin.com/sfYNzQh8

Here's a sample where the slight studder can be seen. It's very slight, but can be seen in this sample a number of times. The sample can be downloaded from here:

https://drive.google.com/file/d/1egL3Pe ... sp=sharing

Vaska

Thanks for the clip.

Testing with master, I don't see/hear any problems. Audio is fairly straightforward stereo speaker setup - no hdmi, spdif etc. Tried with both software playback and VAAPI (Intel) and Alsa and PulseAudio. Everything looks/sounds fine.

Can you narrow down the setup/configuration needed to reproduce the problem?

Thanks and regards
Mark

Hopefully Lost Dog can add his details as well, but I am using HDMI with an nVidia GeForce GT 730 connected to a Yamaha RX-V3900 A/V receiver in a 7.1 speaker configuration. I see the visual studder about ever few seconds. It's a very slight slow down in the video without any slow down or distortion of the audio track. I can use the MythTV menu while watching the video and switch the audio track to the 5.1 and the issue immediately goes away, likewise it returns if I switch back to 7.1.

That sample may not have been the best example. It's more noticeable in this file:
https://drive.google.com/open?id=1O0u_J ... aSLg1alOof

I tried doing an x11grab screen capture but it was fraught with its own issues. I could video the TV directly with my DSLR if that would help see it if no one else is able to reproduce it.

Vaska

Thanks. Second clip plays fine as well with a basic audio setup.

I've just realised however that my ageing Onkyo receiver supports TrueHD - so I'll see if I can test with that. Just need to work around the rest of the 'housebound' family...

Regards
Mark