Problem with AC3 audio in one channel (No audio)

[june]

Hello,

 

A friend of mine has a problem with DVBViewer and i was trying to fix it in his pc today without any luck, so i thought i'd ask in here for a second opinion.

In one specific channel, during the Transedit scan it shows no audio pid at all. I went to "Analyze" and noticed that the channel's audio is set as "Private Data" instead of "AC3 Audio" like the other channels in that transponder. If i open the list on the right, and go to ES PID of that channel, it shows in StreamType: AC3 Audio (ATSC).

 

Now when we went to DVBViewer channel list and tried to edit that channel, the Audio PID was blank. I typed in the APID there (the correct one) and changed the Audio Type to AC3 instead of MPEG. I pressed Apply and then Save to the channel list to save the settings, but i get no audio at all.

 

What else can i try?

 

It definitely isn't a codec or renderer problem, since all the other channels work just fine.

I even tried with a ProgDVB demo to see what results it will show there, and it found the PID directly and audio is playing fine there.

So it makes me wonder, is this a Transedit bug maybe? Or a DVBViewer bug? Or am i doing something wrong?

 

Thanks in advance.

 

Edit:

 

I just tried it with DVBViewer Pro DEMO in my pc too, it had the channel in the preconfigured lists with the correct Audio PID, but still i get the same error like my friend's pc. No audio, even though APID is correct and it is set to AC3 as well.

Edited August 12, 2011 by june

[Griga]

First of all, please tell me the network, reception type (DVB-S/C/T) and country. This is important. Additionally you should follow the instructions given above your post.

 

So it makes me wonder, is this a Transedit bug maybe?

Not a bug, rather a trade-off. Under the following conditions an AC3 stream is fully recognized and accepted as AC3:

 

- Streamtype 0x06 plus AC3 descriptor (according to the DVB specifications).

 

- Streamtype 0x81 plus AC3 registration descriptor or the tuner type is ATSC (according to the ATSC specifications, ATSC = US standard)

 

However, if it is something in between, e.g. stream type 0x81, but no AC3 registration descriptor and a tuner type that is not ATSC, it remains unclear what it actually is, because in the DVB sphere stream type 0x81 is "user private", which means, the broadcaster may use it for arbitrary content. In this case the scanner won't accept it. In the past, when the DVBViewer scanner unconditionally recognized stream type 0x81 as AC3, there were complaints like "why can't DVBViewer play the MTV AC3 stream"? Well, MTV never broadcasted AC3. They used stream type 0x81 for something else...

 

The TransEdit Analyzer is more sophisticated. It displays "AC3 Audio (ATSC)" as a hint in the treeview (left side), indicating that it may be AC3 audio with an ATSC stream type. Additionally the Analyzer checks if the data packets begin with a byte sequence that is typical for AC3 audio headers. If yes, the PID list (right side) also displays "AC3 audio". However, one still can't be sure...

 

Provided it is AC3, DVBViewer should play it happily after the PID and audio type have been entered correctly in the channel editor. If DVBViewer doesn't play it, a suitable AC3 DirectShow decoder may be missing. Try AC3 Filter.

[june]

Thanks for the quick reply!

Channel is DVB-S2 from Greece in Hotbird 13.0e.

 

StreamType is 0x81 ATSC just like you mentioned.

It definitely IS the correct Audio PID, since audio opens with THAT PID in ProgDVB and playbacks normally.

 

I have AC3 Filter installed here in my pc and i tried with it as well with no luck.

 

Audio filters i tried to use are ffdshow, ac3 filter, nvidia audio decoder (all of them work just fine with every other channel i select).

 

Also, the other channels in the same transponder (also with ac3 audio) playback just fine (I checked them with TS Analyzer and they don't have the same StreamType though).

 

For now, i'll tell my friend to use ProgDVB at least for that channel, and i'll advise him to post in here with all the info of his system etc to solve this.

[Griga]

Channel is DVB-S2 from Greece in Hotbird 13.0e.

Frequency? I'd like to check it myself.

[june]

Frequency? I'd like to check it myself.

 

12130.00 H

Discovery channel

[Griga]

Ok, I can see it here now. Unfortunately the channel is encrypted, so I can't test it myself. How encrypted channels / streams are handled in DVBViewer Pro is out of my scope, and I don't know if it is affected by a stream type that is not DVB compliant. Maybe Lars can tell you more about it, but I'm sure he will need information about the device and CAM that you are using.

[Griga]

P.S. I've found a characteristic in the Discovery HD Showcase PMT that can be used to classify such AC3 streams unambiguously. There is an ATSC AC3 descriptor, but it's hard to recognize, because in the DVB sphere the TransEdit Analyzer regards it as "user defined".

 

So from the scanner side this problem (AC3 stream in a DVB network with ATSC-like PMT) will be solved in the next releases. But I'm not sure if it will solve your problem. Looks like decryption is the sticking point, because it must also deal with the PMT content.