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Teletext subtitles being displayed and recorded late


SimonP

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I've been playing with a new facility in MKVmerge where we can now input .ts files and it will output .mkv files with the Teletext subtitles included. This is great but the subtitles are being displayed up to a second behind the speech, which doesn't sound much but it is really annoying when you're hard of hearing and trying to follow what you can hear of the audio, lip reading, and reading the subtitles. To explain:

 

When I watch live TV in DVBViewer the DVB subtitles are in sync, but if I switch to Teletext subtitles they are up to 1/2 second late. The Teletext subs display correctly in recordings played back in DVBv but are late in other players (VLC for example) and my editor (VideoReDo). If I then load the recording (edited or unedited) into MVKmerge it gets a bit worse and they become difficult to follow at times.

 

So, while MKVmerge is almost certainly making the problem worse, it seems to be originating with DVBv displaying and recording the Teletext subtitles late. The developer of MKVmerge doesn't see the problem with other recordings.

 

DVBv/RS is the only method I have of recording so I don't know if this is a broadcast problem or something in DVBViewer but I have tried it with recordings scheduled in RS and manually in DVBv and it's the same.

 

I have re-installed both DVBViewer and Recording Service over existing installations so I don't think it's a problem at my end.

 

Could this be looked at please?

 

While trying to work out which program was causing this, I noticed that if I play a recording in DVBv and immediately try to stop it, it continues to play the video but crashes DVBv and it has to be closed in Task Manager. Also most DVBViewer recordings start with a "glitch" or some kind of corruption at the beginning and this can stop MKVmerge from displaying the subtitles, even though VideoReDo passed it through as if it is OK. I wonder if the two are related? After the beginning my recordings are glitch-free and play perfectly, signal strength is good.

 

The attached recording (193MB) demonstrates most of these issues, but not the "glitch" as I had edited it.

 

Uploaded.to - http://ul.to/osdxnyp5

Mega (copy the whole link) - https://mega.co.nz/#!dxxhhZjY!whWX4SBIiV6HhTAnM_jnJS-vUXJsMBqYcnoNEJG9upY

 

Also, DVBViewer does not see subtitles inside a .mkv container. Could this be rectified? It means I can only use DVBv as a recording device, not a player.

 

 

My recordings are made from BBC HD channels on FreeSat (Astra 28.2) using Recording Service 1.30.1 and DVBViewer 5.3.1.

support.zip

Edited by SimonP
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Estimated download time: ~ 1 Hour 6 Minutes and 0 seconds

you're kidding me ;)

 

 

DVBv/RS is the only method I have of recording so I don't know if this is a broadcast problem or something in DVBViewer

DVBViewer/RS records the transport stream as it is transmitted. If there are timing issues in the recording, you could try 3rd party tools like TSDoctor.

 

 

The attached recording demonstrates most of these issues, but not the "glitch" as I had edited it.

 

You should upload a sample as it is. But don't worry, I won't download it anyway from this file server ;)

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When I watch live TV in DVBViewer the DVB subtitles are in sync, but if I switch to Teletext subtitles they are up to 1/2 second late.

 

DVBViewer Pro doesn't sync teletext subtitles properly with video (yet). It just displays them as they come.

 

DVBViewer GE (see members area, read the ReadMe, can be installed additionally) displays teletext subs according to the broadcasted timestamps, so you may want to give it a try...

 

Teletext subs display correctly in recordings played back in DVBv but are late in other players (VLC for example)

 

Thats not up to DVBViewer resp. the recording eingine, because it records the data as broadcasted (as least in .ts fromat).

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Thanks for the replies, I'll upload a copy to Mega if that's easier.

 

DVBViewer Pro doesn't sync teletext subtitles properly with video (yet). It just displays them as they come.

 

Do you know if this is being worked on? I hadn't noticed this before as DVB subs are usually the default and ProjectX was able to handle the problem but now I need those Teletext subtitles and it's really irritating having them out of sync. I'll take a look at the GE version and see if that is better but am I right in thinking it is stand-alone so I can't use the RS with it?.

 

It is interesting that DVBv displays them in sync when playing back recordings, almost as if it was correcting a known problem? ;-)

 

Is the "crash when stopping a video soon after opening it" problem know?

 

 

Later: I tried the GE version but it doesn't seem to support HD channels or save subtitles so sadly no help.

Edited by SimonP
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Do you know if this is being worked on?

 

Not now. Maybe later. There are a lot of other things to do.

 

but am I right in thinking it is stand-alone so I can't use the RS with it?.

 

DVBViewer GE can work as a RTSP (Sat>IP) client. However, it doesn't delegate recordings to the RS and doesn't communicate with it in this respect.

 

I tried the GE version but it doesn't seem to support HD channels or save subtitles so sadly no help.

 

Of course it does. I frequently watch BBC HD with DVBViewer GE, including subtitle display and recording (particularly Dr. Who :)). Just a question of appropriate settings, I guess. They should be similar to DVBViewer Pro.

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Of course it does. I frequently watch BBC HD with DVBViewer GE, including subtitle display and recording (particularly Dr. Who :)). Just a question of appropriate settings, I guess. They should be similar to DVBViewer Pro.

 

That's odd, I did a full scan and it didn't find any of the BBC HD channels so I copied the channels.dat file across and then it saw them in the channel list but couldn't tune them. The S2 box was automatically ticked so it knows that I'm using an S2 tuner. Also I just checked again and it is displaying but not recording the subtitles.

 

But never mind, I really want to use this new facility in MKVmerge but having the Teletext subtitles out of sync is spoiling it so I guess I'll have to find a new method of recording my TV programmes, which is very disappointing as I have everything else working nicely now.

Edited by SimonP
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My recordings are made from BBC HD channels on FreeSat (Astra 28.2) using Recording Service 1.30.1 and DVBViewer 5.3.1.

 

I've checked the sample with the TransEdit 4.0.7 Beta Teletext Analyzer and Preview functions (see members area -> beta section).

 

- Drag & drop the file on the TransEdit icon or the TransEdit Main Window.

- In the Analyzer Window right-click the teletext stream -> Teletext/Subtitle Analyzer.

- In the Teletext/Subtitle Analyzer.Window select page 888

- In the Analyzer Window right-click the video stream -> Preview

- Right-click the Preview Window -> Subtitles -> Teletext page 888

 

The Teletext Analyzer displays a teletext page as soon as it is available resp. arrives, which means, teletext subs usually too early.

 

The Preview Window displays teletext subtitles according to the broadcasted presentation timestamps, which means, they are synced with video as intended by the broadcaster.

 

Now in this case even the Teletext Analyzer displays the subtitles too late, and the Preview far too late. Since DVBViewer and the Recording Service record all streams as broadcasted (at least in TS format) without applying delays, changing the mux or time stamps, it's clearly the broadcaster's fault.

 

I'll have to find a new method of recording my TV programmes,

 

Forget it. It's a waste of time. You have to find a tool that is able to remux the stuff and/or shift teletext subtitles towards the past. That's all you can do.

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Thanks for looking into it, Griga, I must admit I did wonder if they were being transmitted late but they display in sync on the TV and ProjectX seems to handle them OK so it seemed unlikely. I'll look into it some more and contact the BBC about it to see what they say.

 

I will probably stay with DVBViewer as everything else is working nicely and the Android app is incredibly useful so I'd lose a lot of functionality by switching to something else but trying to get the subtitles working without having to run the files through several different programs is very frustrating.

Edited by SimonP
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