SPDIF drop outs with Media Portal

[greath]

MediaPortal Version: 0.2.3.0
Windows Version: Win XP Professional SP2
CPU Type: E6600
Motherboard: X1250
Sound Card: Club Theatron
h.264 Video Codec: Core AVC
TV - HTPC Connection: VGA

Firstly, with my first post, let me thank you for a great piece of software.

Now, onto the problem that I am having:-) When watching 1080p backups I get audio drops on the SPDIF link every couple of seconds. I've tried several things to get around the problem, and it can be done, but there is no one setup that I can then use for every video I play. So in the end I would like to know why it happens and it's driving me crazy:-) It also wouldn't be bad if it wasn't for the fact that Media Player Classic can play the files with no glitches or audio drop outs at all.

I've tried several graphs in graphedit that all work, yet when configuring Mediaportal to use those same codecs for H264, Audio and Audio rendering the SPDIF dropout still happens.

I've tried FFShow for H264 decoding and for audio, Core AVC with FFDshow and AC3 filter and MPA decoder, and Cyberlink with FFDShow, AC3 filter and MPA decoder. All have the same result.

Another odd thing is that if I don't use SPDIF passthrough, but decode it in the PC, then pass it out as AC3 640 over SPDIF it works. Only in passthrough mode does it glitch.

My suspicion is thread-priority within Mediaportal. Is there a way to boost the priority not of Mediaportal but of the threads for audio, or do they run at the same priority as Mediaportal, as it also happens if I boost the priority of Mediaportal.

Any suggestions would be appreciated.

Thanks in advance.

[rtv]

Most likely:
- the audio codec is configured wrong
- your soundcard has a very weak reference clock.

Try e.g. if it works in Windows Media Player or using Wave Output (do not forget to change the codec as well then).
Even the cheapest realtek onboard audio does work okay for S/PDIF using MPA (choose 16 bit) or ffdshow.

Only some Asus boards which use e.g. ADI (Soundmax) solutions are known to cause issues.

[greath]

Thanks for the reply.

At first I thought it might be the sound card, as I am using optical SPDIF over a 3m cable. But the fact that I don't hear any drop outs when playing through Graphedit, or WMP11 or MP Classic made me think otherwise. Also, if I use the PC to re-encode the audio internally without passthrough but by decoding and then re-encoding to AC3 at 640kbps, and then let the sound card take the 640kbps decode ( I have a Club3D Theatron that has Dolby Digital Live ) then it also works OK, though the Dolby Digital live annoys me as it sounds too echo-like and my external decoder should be able to decode the AC3 and DTS over SPDIF.

Is there a way to see the graph constructed by Mediaportal, or some way to save the graph used to open in graphedit later? Also is there a way to get the player in Mediaportal to open a graph?

OK, after some playing with graphs, I have reached a conclusion and managed to get the audio drops to disappear, but am not sure why it happens only in Mediaportal and not when using any other Directshow player. It appears though that the first stage of the chain for processing audio has to output PCM and not SPDIF. It also has to do with the merit of filters. Below, when I say "working", I mean no SPDIF audio drops.

a) When opening the file X with graphedit it would have in the audio chain MPA decoder, then followed with AC3filter, and then the directsound renderer. This worked as MPA encoder was configured to output PCM to speakers, AC3filter took PCM and re-encoded to AC3 640 over SPDIF. Also avoided going back through the sound card and the Dolby Live.

b) When MPA decoder was set to output SPDIF and AC3filter removed it also worked.

c) When MPA decoder was removed and only AC3filter was in the chain outputing SPDIF this also worked. Note, to get this to work directly when opening file X I needed to increase the merit of AC3filter using GSpot as even though AC3filter was set to the preferred filter it didn't have a merit higher than MPA decoder.

Then, moving to Mediaportal, I couldn't get any filter that outputs SPDIF to work without drop-outs. I tried

a) Audio codec set to AC3filter with SPDIF passthrough for AC3 - dropouts.

b) Audio codec set to MPA Decoder with SPDIF output - dropouts.

Only when the codecs above were set to output PCM, which was then re-encoded by the soundcard using Dolby Digital Live before being output over SPDIF did it work.

So this results in two problems - firstly a loss in quality as I get a two stage decode process in both the PC and the external amplifier. In addition, the Dolby Digital Live of the sound card sounds like a church.

Does Mediaportal run the audio at a low priority? As it would appear that the hardware can transmit SPDIF without dropouts so the phyical cable connection seems OK and other directshow players are OK. But any filter I use in Mediaportal set to output SPDIF will dropout, only filters that output PCM work. Then, since I cannot chain filters in Mediaportal, I have to suffer Dolby Digital Live because I can't use AC3filter after MPA decoder to bypass this output stage in the soundcard.