RS: No audio track recorded with some specific channels

[allanlee]

Encountered a problem for quite some time:

 

Using DVBSky T680C with CAM to view/record Cable TV.

 

For some specific channels / transponders, RS is recording only the video track although "all audio tracks" ticked. (see sample2)

 

The only temporary solution for me is to tick "whole transponder" in order to include audio tracks. (see sample3) However this will result in very huge recording files and some problem with downstream processing.

 

At the meantime, I noticed that playing the same channel in DVBViewer do have audio, and the timeshift file has audio too (see sample4)

 

I've dumped ~40s of that whole original transponder with TransEdit for your investigation (see sample1). All channels in that transponder have this problem with RS.

 

All samples could be downloaded from here and support file attached.

 

Thank you very much in advance.

support.zip

Edited December 15, 2016 by allanlee

[Griga]

For some specific channels / transponders, RS is recording only the video track although "all audio tracks" ticked. (see sample2)

 

Your uploads made it possible to detect the reason. The AC3 audio track is not broadcasted in an ISO compliant way. The PES start code in the audio data packets should be 00 00 01 BD but is 00 00 01 C0, which is correct for MP2 and AAC, but not for AC3. You can see it in the TransEdit Hex Viewer at the beginning of the orange part (which is the PES header).

 

 

The recorder checks the PES start code carefully in order to find out whether the stream is decryped correctly and recording it can start, because usually it takes some time until the CI/CAM delivers unencrypted data after tuning. However, in your case the expected start code for AC3 audio never arrives. It doesn't matter in whole transponder recordings, because in this case the recorder simply records everything that arrives without checking wrong and right.

 

We already encountered this kind of bug some years ago on BBC HD - see here - and I provided a tool for fixing it in recordings, because some players don't play AC3 with a wrong start code. Unfortunately there is no way to work around it before the data gets recorded. Nevertheless I will think about it...

 

If you want to rework the whole transponder file after it has been recorded and make it a normal recording you can do the following:

 

(1) Let the BBC HD Fixer tool correct the wrong start codes in the file (you will have to enter the Audio PID in question).

 

(2) Let the TSPlayer Tool from the download area -> tools section extract the desired video/audio data into another TS file. More about it in the manual, particularly in the conversion chapter. The TSPlayer uses the recorder engine for re-recording. That's why the start codes must be fixed first.

[Griga]

Unfortunately there is no way to work around it before the data gets recorded.

 

...but a way to patch it. I've just found an old plugin that does something similar. I only had to rework it a bit. Here it is:

 

PatchAC3StartCode.zip

 

It has no UI, which would be useless anyway when used with the Recording Service. Perform the following steps:

 

(1) Create a Plugins1 sub-folder in C:\Program Files (x86)\DVBViewer\Plugins. Store the plugin in this sub-folder.

 

(2) Create additional Plugins2, Plugins3... sub-folders if the plugin will potentially be used for two, three... recordings at the same time. Copy the plugin to these sub-folders.

 

(3) Stop and re-start the Recording Service and try to record one of the channels in question.

 

The plugin checks if the currently tuned channel has an AC3 audio track. If yes it patches the PES start codes to 00 00 01 BD in any case before the recorder sees them. Please note that the plugin is not able to handle more than one AC3 audio track at a time. The AC3 track must be the main track of the channel (not one of the secondary tracks shown in the DVBViewer channel list).

 

I've tested it with the Recording Service and it worked in a simulation that used your whole transponder file as source for recording. However, it's a quick & dirty hack. There may be unknown side-effects, and I'm not sure if it really works for two recordings at the same time. You must try...

[allanlee]

 

I've just found and old plugin that does something similar. I only had to rework it a bit. Here it is:

 

PatchAC3StartCode.zip

 

 

It works!!!

 

So far no bug no side-effect observed. Will let you know here if found any in the future.

 

Many thanks for the patch plugin!

[logifuse]

I'm using this patch with the 1.33.02 recording service (thanks, BTW) & am thinking of upgrading to Media Server 2, is this patch still needed, & if so, will it work with the new version?

 

Thanks.

[Griga]

4 hours ago, logifuse said:

is this patch still needed

 

Yes, if the broadcaster is still using the wrong start code.

 

4 hours ago, logifuse said:

will it work with the new version?

 

Yes.

[logifuse]

Thank you for that. I'm hoping to try the upgrade later this week.

 

ABCHD in Australia is the problem channel for me. Without the patch, it will often record with no audio track.