Need help correcting audio problems

[Bunter]

Hi
I have a Panasonic Freeview HDD recorder which can copy aired programmes recorded to its hard drive to Blu-Ray disk at UK high def res. I want to archive these to a DNLA server but have encountered audio issues when ripping the BD using MKV.

The audio is fine during advert breaks but continually breaks up during the actual content. For this reason I suspect audio encryption is the likely cause. For info the BD play back perfectly in the Panasonic blu ray drive and in non-Panasonic drives too. MKV reports the following on completion.

AV sync issue in stream 0 at 0:00:00.160 : video frame timecode differs by -40ms
AV sync issue in stream 0 at 2:37:44.360 : video stream has 5 frames with invalid timecodes
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Has anyone encountered this before and found a solution please? I'm not very technie.

Many thanks in advance for any help with this.

Bill

[jinx100]

The sync problems that MakeMKV finds are usually insignificant and 40ms would not be any problem.

The video and audio tracks in the MakeMKV MKV file are identical to those on your Blu-Ray disc. How are you playing back the MKV file? The player or a limited data rate to the player may cause playback problems.

[Bunter]

The sync problems that MakeMKV finds are usually insignificant and 40ms would not be any problem.

The video and audio tracks in the MakeMKV MKV file are identical to those on your Blu-Ray disc. How are you playing back the MKV file? The player or a limited data rate to the player may cause playback problems.

Thanks for the reply, I'm playing back from the MKV file stored on my Mac Studio (M1Pro) SSD using VLC 3.0.17.3 for Apple Silicon. I don't think there's a bottleneck there.

[Bunter]

Interestinly, when I try to extract the audio from the mkv using ff-mpeg (using ff-Works), which is my normal tool to process SD content to convert so I can import to iMovie to remove adverts, I get a very long error log. Would it help to post that?

[jinx100]

You're right, that playback combination of a Mac, VLC and an SSD should be flawless. A long list of ffmpeg errors would not help me but maybe look at the MKV file with MediaInfo or MKVToolNIX to see what type of tracks are within the file.

Maybe British TV changes audio formats between the advertisements and programs. I'm US based so unfamiliar with your TV signal and Freeview recorders. What container does the Freeview recorder use? Can you use that format directly to store your movies or use ffmpeg to convert it to an MKV container? I'm assuming you have a collection BR discs created by Freeview so that is why you need MakeMKV. Recording OTA TV is easy in the US and doesn't need MakeMKV.

Edit:
Does the Freeview BR disc use encryption like commercial BRs? Try playing the disc directly from VLC. VLC also has a rough conversion capability to other containers. Also, look at VLC tools-codec info which has a statistics tab which shows any dropped video or audio frames.

Sorry to just be throwing ideas at you.

[Bunter]

Don't apologise, you're helping so that's appreciated, thank you.
Attached is what is reported by the tracks using MKVToolNix.

Screenshot 2022-10-11 at 17.06.13.png (201.19 KiB) Viewed 4966 times

MKV sees reports that the audio is AAC. The container on the BD is m2ts, and MKV is the only thing I have that reads these (VLC won't play the BD at all nor the files, and ffmpeg cannot process these files). VLC reports the files have 0:00 duration. Other commerical BD work fine directly from the BD with VLC for me.

I do have a work around although it's a very dirty hack so if this is a problem no one has encountered before it probably is just my perculiar set up.

Cheers

Bill

[jinx100]

That file information looks quite ordinary. Video - H264 and audio - AAC are common and should be easily decoded. You have only one audio track so no chance of picking the wrong track. The Freeview BR discs don't play with VLC but they must play in an ordinary BD disc player, right?

What is your work around?

[Bunter]

That's correct, the BD do play in a normal BD player. The work around is to simulataneously record anything I really want to keep in SD and HD, then copy both to my Mac, MKV the video from the HD files and ff-mpeg the audio from the SD files and recombine hoping for zero audio sync issues I did say it was dirty!

Bear in mind I'm not trying to make an archive of anything I can easily replace or buy, nearly all of the content I've kept from years of different Freeview recordings is music broadcasts that very rarely are repeated or released as DVD. Until I purchased the latest recorder I was stuck archiving SD content, I used to autocopy via DNLA using Twonky to my Mac. The fact the new recorder allows me to copy HD content onto a disk has piqued my interest.
Cheers
Bill

[jinx100]

Reading about Freeview in Wikipedia the HD channels do have copy protection while the SD channels do not. Possibly there is extra audio encryption as you first suspected. Then patching the SD audio with the HD video may be your only choice.

For HD there can be a second, program description, audio channel. If MakeMKV mistakenly combined these two this may explain why the commercials are clear while the program is distorted. This seems unlikely, though.

If someone familiar with Freeview doesn't doesn't answer here, try some Freeview forums. This question must have been asked.

Edit: It has. See viewtopic.php?f=8&t=16642&p=57552&hilit=freeview#p57552

[Bunter]

Thank you Jinx, sorry been away for a bit so missed your reply.

[jinx100]

Since AAC is just an audio compression method, it would be nice to know how many channels are inside the compressed file. Maybe it is switching between 2.0 and 5.1 from commercial to program.

Since the disc plays in a BR player to your TV, try putting the .MKV file on a USB portable storage device and plugging into your BR player or TV to see if it sounds better than on VLC. Most TVs and many BR players can accept .MKV files.