Recording Glitches - Debug Advice?

[andrewj]

Hi,

I use NPVR to record mainly HD TV in the UK, using a pair of Hauppage WinTV-dualHD DVB devices. While the recordings are fairly high quality, each typically has a handful of "glitches" where the sound and image are disrupted for about 1s. I have confirmed that the glitches are present in the original MPEG-2 files exported by NPVR, and are not an artefact of the conversion to MP4 although this can make the fault a bit more "obvious".

The glitches occur on all channels, although they are rarer on SD recordings. We rarely if ever see the same issue on live TV, so it's not related to quality or strength of original signal. 

The recording system has a 12-core gen 11 i7 processor with 32GB RAM and is usually lightly loaded at common recording times, so system capacity is unlikely to be an issue. 

The glitches also occurred on my old i7-based system. However in December through January this year I temporarily moved recording to a much older system with a Xeon processor (using the same tuners and signal source), and the frequency of glitches was noticeably much lower. This suggests to me that there might be some oddity specific to the combination of hardware, or other software on the newer system.

What I'd appreciate at this stage is guidance on how to log NPVR and related activity so we can find out what's happening when a glitch occurs, and if NPVR offers any diagnosis of the issue. Unless I'm missing something there are no obvious "log level" settings in the NPVR client or web settings, is that correct?

Thanks
Andrew

[andrewj]

I have rescued my logs for yesterday, and have a sample recording using which I should be able to identify the timing of a glitch. If I can do this I'll share the logs.

[BrettB]

The glitches occur on all channels, although they are rarer on SD recordings. We rarely if ever see the same issue on live TV, so it's not related to quality or strength of original signal. 

When you say "We rarely if ever see the same issue on live TV", do you mean when watching TV on a physical TV or in NPVR via "Watch Live"? There are some internal difference in how live TV vs recordings are viewed in various clients and actually watching live is more complicated than watching a recording. Also, real world evidence has found that the tuners in TVs are typically "more powerful"/better quality/etc. than computer counterparts and they can better handle lower signal strengths and/or small drops than the computer tuners. So, just because an actual TV doesn't have a signal problem doesn't mean that the computer tuner won't have a signal problem.

Your symptoms really do sound like a signal issue. Are there any splitters you can try removing for testing? Do you have an amplifier? Over-amplification can also cause problems.

The recording system has a 12-core gen 11 i7 processor with 32GB RAM and is usually lightly loaded at common recording times, so system capacity is unlikely to be an issue. 

The glitches also occurred on my old i7-based system. However in December through January this year I temporarily moved recording to a much older system with a Xeon processor (using the same tuners and signal source), and the frequency of glitches was noticeably much lower. This suggests to me that there might be some oddity specific to the combination of hardware, or other software on the newer system.

Because NPVR basically just takes the digital transport stream that it receives and writes it out to disk directly without processing of any sort, the recording process does not need a very powerful system at all. However, one place were some users (myself included in the distant past) have seen "random glitching" in recordings related to PC hardware is when there is heavy disk access on the recording drive. If the drive is being overloaded (typically by other, non-NPVR processes) and having a long write queue, then it seems like some of the TS can get "dropped"--at least with some tuners/connections.

If you can, you might try to do your recordings to a local (not a network) drive which is dedicated to NPVR recording in order to isolate the recording disk activity. (Maybe you already are doing that...)

What I'd appreciate at this stage is guidance on how to log NPVR and related activity so we can find out what's happening when a glitch occurs, and if NPVR offers any diagnosis of the issue. Unless I'm missing something there are no obvious "log level" settings in the NPVR client or web settings, is that correct?

On the NPVR Settings screen, if you press the Control key, a new button "Enable Verbose" will be displayed. Be careful about turning that on as it will make the logs much busier (and turn over more often resulting in less time covered by the 4 logs in the rotation). I'm also guessing that enabling verbose logging won't really help in your situation since it causes more logging of all the "internal processing" of NPVR, but when it is recording, the digital stream is just being directly written to the disk without any real internal processing.

[andrewj]

Thanks Brett. Re your first point yes, I was comparing live viewing on a (very good) TV vs recording on the PC. Also the odd glitch is not unknown on the TV. The only amplifier is upstream from everything and has separate outputs for each room, but there is a splitter on the PC feed. I can try removing that and running with just one tuner.

Disk bandwidth shouldn't be an issue. Recording runs to a dedicated local SSD.

I'll see if I can track down the moment of a glitch in my saved logs and see if NPVR reports anything useful. Otherwise I'll have to experiment with the signal path.

[Bobins]

My personal experience is that invariably "blips" in a recording are caused by signal quality issues and as BrettB said, TV tuners are much more tolerant of signal issues than PC based tuners.
Aerial splitters / cable joins & damage are notorious for causing signal degradation. Also foliage (e.g.trees) obscuring the aerials line of sight to the transmitter can also be an issue. (Used to cause picture ghosting in the old analogue days but now causes "blips" in the received digital stream).

The NPVR logs won't necessarily show a "blip" in the recording stream however they would give us a clue on signal strength/quality at the point of tuning the channel.

Ray

[mvallevand]

If you decide to share a sample only an mpeg-ts (not an mp4 which will amplify any problems) same would. The splitter at the PC will have a negative impact.

If you use the yauiclient you can see some diagnostic information as shown here https://forums.nextpvr.com/showthread.ph...#pid601397 that might give you an idea of your stream quality. Strreams rarely are perfect.

Martin

[andrewj]

Thanks chaps. I've just worked through an example program for which I have the logs.

The error occurs in "Walking with Dinosaurs" at 25'22 and is visible in the .ts file. Recording started 2025-06-22 18:22 (18:25 official start), so the error occurred at about 18:47:22

The Tuner 1 log and NRecord.log both show recording starting & stopping, no specific activity at the error point. Attached for you to have a look and see if you can see anything. 

I have uploaded a copy of the .ts file to https://www.andrewj.com/public/Walking%2...8251915.ts in case that is useful.

[mvallevand]

The file does a few gaps so yeah not much to do to help. The logs would be better if you sent the full logs, nothing in them about the recording, always send the zip file that NextPVR creates for you.

You don have a significant number (300+) of bad scheduled recordings on channels that are no longer in your channels list that you should take time to clean up.

Martin