The VideoLAN Forums

My pc is linked to a Sony Bravia Tv - I was using VGA cable + analogue audio but have switched to HDMI using the Nvidia sound card.

video playback, on default settings, is still fine, specifically I can use the fine speed controls to speed up video playback by 10, 20 % etc with no loss of audio.

the default audio setting is direct x + primary sound device

but here's the puzzle - on the drop down audio device menu there is also an option for "Sony TV + Nvidia hi-def audio". If I select that then my audio at normal speed sounds exactly the same but as soon as I go 10% faster , or any speed other than normal - my sound vanishes.

Why is that, why does VLC work better on a generic setting that an a correct, specific device selection ?

It is no problem for me to stay with the default primary sound... selection; I just would like to understand why I lose faster/slower audio when I cnage only that 1 setting.

You probably enabled S/PDIF pass-through.

I am pretty sure that it is not the SP/DIF passthrough toggle , because I tried that both way around.

but I will re-test on that PC ( it si not the one I am typing from) in case I missed some combination of device & SP/DIF setting.

I am 99% sure that if I just go in and change audio device - but nothing else, then the audio will fail at faster speed.

Why should SP/DIF option prevent faster audio from working anyway - is that a bug or a limitation of the SP/DIF spec ?

UPDATE - it IS the enabling of "use S/PDIF if available" that causes the speeded up audio to vanish. its not toggling between primary sound /Sony TV audio device

but WHY ? Are there limitations for anyone who DOES elect to use S/PDIF as therir audio connection ?

PS there is no S/PDIF output on the PC - its your basic DELL pc with on board realtek ( not in use) but i am using the video card NVidia HD audio

Resampling coded audio is impossible. Your HDMI or DP monitor probably supports pass-through even if it is not physically using S/PDIF.

Resampling coded audio is impossible. Your HDMI or DP monitor probably supports pass-through even if it is not physically using S/PDIF.

ok - I see this also on other thread s after a forum search.

but please confirm. if it s OK to use an S/PDIF connection - like an optical or co-ax cable , from a PC sound card to some external audio amp, with the "use S/SPDIF passthru " box is NOT ticked and then still be able to change speed without losing audio ?. I don't have the facilities to test that, but it is implied, not confirmed, in a related thread.

NOw a suggestion: the "passthru" word does NOT appear on the preference screen. it just says "use S/PDIF if available" which does not have the same meaning.
surely if would be better to call that box " enable S/PDIF passthru" and put a warning in the the help text for that box re resampling ?

(bacause as I understand this & other threads - it is allowing passthru that is the issue, not using the connector per se )

? finally - S/PDIF is a 10+years old protocol used for digital audio via optical or co-ax connectors, one or both of these are known as TOSLINK; and that is now old technology mostly superceded by HDMI. Because it has less bandwidth than HDMI and can only support multichannel sound over short distances. ? I just want to get all the acronyms clarified. if HDMI is technically superior then clearly that is the way to go as it is eill supported by consumer Av receivers and TVs

I got into this whole thing because I wanted to see how far I could transport the embedded multichannel audio from .AVI / .MKV. media files, through my setup. the NVidiaiHD audio driver should be a multi-channel device and though I only have 2 channel sound, the TV does have various pseudo surround effects built in, so I wondered if, via HDMI, it would accept and make use of a 5.1 audio feed.
But on inspection, VLC down mixes and sends only stereo - does it detect somehow that the TV is only really a 2 channel device or does it default to stereo unless it sees positive feedback via HDMI that is is dealing with a multi-channel audio device. I now think maybe that TV can only accept stereo in via HDMI, and will base wll its pseudo sound processing on that feed. it may behave differently when it has a 5.1 sound source from its own internal TV tuner but detail is hard to come by. I did read that many tvs only output 2 channel stereo on their optical out connector, for feeds received via external HDMI , from blu ray etc. but will output 5.1 when received from their own internal tuners

I have somewhere some USB driven surround sound headphones, so I will dig them out & see if VLc will deliver 6 channel sound to those

if this multichannel aspect is within another thread or better discussed in a new one, please advise

The option is called S/PDIF because it makes VLC use S/PDIF framing for audio output, not because the physical link would be S/PDIF or HDMI or whatever. That seems perfectly reasonable to me in the VLC preferences.

well let's not quibble about a label:)
back to the multi channel issue - should I be able have VLC regard the Sony TV as a multi channel audio device and send all 6 avi channels to the TV for downmixing there ( via the HDMI cable/ Ndidia audio driver ? The advice I have when discussing another media player is to go this route -
why is VLC electing to downmix ?

for HDMI, if you use PCM and the normal HDMI audio driver, it should work.

for HDMI, if you use PCM and the normal HDMI audio driver, it should work.

confused now - I thought PCM was for 2 channel only ?

also: can't see where to select PCM - on the audio tab I only see output module, device, & dolby surround options ?


looking at media files that I have : a typical .AVi - movie or tv series will say, in right click properties details - channels 6, plus a bit rate. windows can't tell me what's in an .MKV but I would expect 6 channels in a hi def 720p or 1080p rip.

Turn off S/PDIF pass-through.

Turn off S/PDIF pass-through.

i did that a while back after previous advice in the thread.

so am I making this too complicated - are you saying that "use PCM" simply equates to " do not use S/PDIF " ?

not always

Without S/PDIF, you should use your "HDMI Audio device" normally with VLC. and the data will be PCM.

not always

Without S/PDIF, you should use your "HDMI Audio device" normally with VLC. and the data will be PCM.

OK - thaks for clarifying I think, but I will check ( as we're talkgin abotu a different PC ) that 6 channel avi is being turned into stereo though

Then, please share the logs. Try with 2.1.0-pre1 too.

Then, please share the logs. Try with 2.1.0-pre1 too.

I did more checking...

the limitation is with Sony bravia TV - or Windows!

control panel - sounds... says that SONY TV is a 2 channel stereo device - no other options, even though it's on a HDMI connection.

it actually lists 3 x NVidia HDMI, options , on ports 1, 2, & 3, but says 1 & 2 are not connected and that TV is on 3.

So I guess that dictates how all media players will behave.

Seems I'd have to be going - PC ...hdmi... surround sound receiver...hdmi... TV in order to get multi channel.

I guess the TV is what limits things - rather than add a downmixer , Sony have set it to insist on downmixed inputs on all of the HDMI-in ports

I will see what happens when I connect my USB 5.1 headphones, and switch the audio to those, but not tonight

I have the same problem with my home TV, albeit Samsung. It could also be that the TV supports Surround but exclusively with (S/PDIF) pass-through.