Audio Sync issue (1 Viewer)

[PoBear]

Hi

This is a little convoluted so please bear with me.

I record UK Freeview programmes from a PCTV DVB-T usb device using MP 1.7.1. The programmes for SD TV are MPEG-2 in a .TS contained. I convert the Programmes to DIVX format using FFMPEG and then edit them to remove the commercials etc.

The converted files regularly have audio sync problems, varying usually from +750ms to -750ms and anything in between, there is no pattern to the offset, it varies from day to day and is not specific to a particular programme or channel. However, I often duplicate the recording on my MCE box, these recordings are processed in the same way but never have the audio problem, so it is not related to the original broadcast but does appear to be specific to MP.

Does anybody have any ideas how to correct this or how to diagnose the problem in more detail.

Thanks

 

[mm1352000]

Hello

However, I often duplicate the recording on my MCE box, these recordings are processed in the same way but never have the audio problem, so it is not related to the original broadcast but does appear to be specific to MP.

When you say MCE do you mean recording with WMC? ...so the container would be different - dvrms or wtv?
If the container is different it could explain the problem. Don't assume that whatever editor you're using will handle all containers with the same "ability" (no bugs, sync good etc.). The container often (and certainly in the case of TS) includes the critical timestamps that keep stuff in sync. Therefore a difference in container could explain the difference in output.

Also be aware that with TS, the PCR [edit: PCR = program clock rate] tends to be associated with video... which means that if you're re-encoding the video you have to be careful not to lose that information, or you'll have problems exactly like this.

What editor are you using?
Is the sync offset (?):

• constant through the output
• drifts through the output
• constant during sections but changes at joins

Have you tried removing the ads without re-encoding the video and seeing if the same problem occurs?

mm

 

[PoBear]

Thanks for replying

Although the containers are different WTV vs TS the actually video is identical with the exception of length and even then it is only a few minutes, I've done tests converting the videos from both systems and have produced files that are literally only a few bytes different in size.

The audio is offset by fixed amount throughout the recording, but is a variable value from one recording to another, even consecutive recordings on the same channel can have different values.

I use MCBuddy (FFMPEG) to convert all of my SD recordings from the original MPEG-2 TS to XVID in an AVI container and then use VirtualDub to edit out the start/end and commercials, it is at this point that I have to adjust the audio. I also have the problem if I just use VirtualDub and convert to DIVX directly.

 

[mm1352000]

Although the containers are different WTV vs TS the actually video is identical...

Hmmm, like I said the container can make all the difference. Sync doesn't depend on the video or audio content itself.

The audio is offset by fixed amount throughout the recording...

...even consecutive recordings on the same channel can have different values.

These statements suggest that the programs you're using to process the recordings aren't correctly preserving and/or interpreting the timing information in the recordings.

TV Server doesn't control, influence, or care about video-audio sync. Sync in the source stream itself (including recordings) depends entirely on timestamps injected by the broadcaster, and we don't modify that. A TV Server recording is for all intents and purposes just a broadcast stream written to file.

The sources of sync issues are:

• the broadcaster
• post-processing
• playback

If the original recording doesn't have sync issues then you need to look at the other two possibilities.

I use MCBuddy (FFMPEG) to convert all of my SD recordings from the original MPEG-2 TS to XVID in an AVI container and then use VirtualDub to edit out the start/end and commercials, it is at this point that I have to adjust the audio. I also have the problem if I just use VirtualDub and convert to DIVX directly.

As above: post processing of any kind can introduce issues.
I can't give you a detailed explanation as to why the same processing for a WTV file is okay. At the highest level the explanation is that WTV is [very] different to TS, and MCEBuddy and will handle it differently. I note that the AVI format itself has limitations. It really isn't the best choice for a container these days.

 

[Owlsroost]

I agree with all of mm's comments.

I suspect that MCEBuddy is making invalid assumptions about .ts files (like ignoring/incorrectly processing the video and audio PTS timestamps).

Have you tried using another tool like VideoRedo to process the files ?

 

[PoBear]

I'm sorry guys but I really don't believe that the container has the effect you are suggesting, I've stripped out the TS out of a WTV file and then processed and the audio remains in sync.

I'm not ignoring the processing I do as a source of the problem, but the problem never happens on MC7 and always happens on MP so I think it reasonable to look at whether MP can be the cause.

 

[Owlsroost]

Do the .ts files from MP play correctly (in sync) in other players e.g. Windows Media Player & VLC ?

I also record UK Freeview, and I've edited and converted to MPEG-2 program streams (for DVD use) quite a few files from MP without a problem using VideoRedo (mostly from the ITV1 SD channel)

If you 'strip out the TS out of a WTV file' with a tool it's been processed with that tool....

 

[mm1352000]

I'm sorry guys but I really don't believe that the container has the effect you are suggesting.

Well, take my comments or leave them. If we can't convince you then I don't know what would.

I've stripped out the TS out of a WTV file and then processed and the audio remains in sync.

As Owlsroost said, stripping the TS out is processing... and I'm not sure that the original WTV recording isn't significantly processed when it is recorded. TS is as close as you can get to the original broadcast. WTV is at least one step removed from that.