Hi
My problem is that I can’t get digital AC3 output in MKV or AVI video files to my TV, although, curiously the AC3 audio does work in mp4 files. Other audio streams (AAC, MP3, eg) in video files work fine.
My set up is WD Live Hub via HDMI to Samsung LN22C350 22inch LED TV. The WD audio output is set to Digital Pass Through.
The TV specs indicate it should receive and decode the 5.1 AC3, and indeed it works fine if the the files are, as mentioned, mp4 files. The exact same streams packaged in mkv container will not play audio however. While I suspect the issue is with the TV, I don’t understand how this would happen … doesn’t the WD Live Hub act as decoder, or at least unpackage the vid and audio streams from the mp4, mkv, avi, etc container and send vid / aud out? If the TV can handle the ac3 stream passed through from an mp4 container, could it be that issue IS with the WD?
Thoughts?
To keep this on track, I am aware of the option to use stereo-out from WD, and that does work., but I’m aiming to get the digital audio signal to the TV. (The LCD is a secondary viewing source. The Hub is also routed via an HDMI switch to a projector, with digital out to an AV Receiver. That all works fine regardless of file type. I have also confirmed that the switch is not the issue).
Also, this is not related to the mkvmerge issues I’ve seen discussed elsewhere.
I realize this is kind of petty because I can get sound, but 1. it’s picqued my curiousity and 2. I bought this TV specifically to do this after struggling with a less HD compatible monitor for a while, and so I guess I’ll take it back if it is the problem.
THANKS
No, if you set it to DIGITAL, it’s doing PASSTHROUGH. So, it leaves it to the downstream device to decode.
I’m the reverse… AC3 in MP4 does NOT work, but it DOES work in MKV. I’m connected to an AVR.
I don’t think AVI can do it at all ,but I’m not sure.
Thanks Tony.
I know it’s doing what it calls passthrough, but I figured the WD at least separated the audio and video streams decoding the video and passed through the separated audio. That would mean that it sends through a separated audio stream that would be the ac3 stream. Not so?
It is just passing along an encoded AC-3 stream for the downstream device to decode. If the downstream device (whether TV or receiver) can’t then decode the AC-3 stream, then the result is no audio.
I’m thinking that your TV can’t decode AC-3 from HDMI (but I could easily be wrong).
My guess would be that the “reason” it works from .mp4 for you, is that the .mp4 is just outputting a 2-channel PCM stream and not the full 5.1 AC-3 stream, but without an HDMI analyzer to see what’s bening sent to the TV in each case, I’m admittedly guessing.
Funnily enough, MP4 AC-3 support is kinda messed up on the Live, which outputs a downmixed PCM signal as far as I can tell.
Like Tony, I connect to an AVR and 5.1 does not work from MP4s.
MKVs and AVIs work fine with 5.1 AC-3 for me.
Thanks for your thoughts Roofing Guy.
Unfortunately I don’t think that’s what’s happening to me, or maybe I don’t understand some of what you’re saying.
Regarding your thought that the TV can’t decode AC3 from HDMI, it does decode AC3 in certain vid types (mp4, or mpeg/DVD). I’ve tried it with mp4 and dvd/mpeg/vob files that have no other streams except the 5.1 AC3, with the WD set to Digital Passthrough. They play fine. FIles with only 5.1 AC3 in mkv or divx/avi do not play the audio.
Regarding your guess that “the .mp4 is just outputting a 2-channel PCM stream and not the full 5.1 AC-3 stream” I’m not sure what you mean because the mp4’s contain ac3 only. Are you saying that the WD changes the AC3 to PCM for MP4 and DVD files (but not for MKV or DIVX/AVI) and then sends that on its digital passthrough?
I’m thinking I should approach this from a different angle and ask who has a a TV which plays audio in MKV or DIVX/AVI files played on by the WD HUB played through HDMI with digital audio passthrough to the TV? I can return the TV if there is a better option. I guess maybe that should be a new thread.
Thanks much.
Johny, yes, that’s what he’s saying. For certain formats in certain containers, the WD just outputs PCM instead of the raw stream. Some devices CAN play that, others CAN’T.
I’m creating a few test cases right now, and I’ll try them on my receiver that plays everything and see what format is doing what.
Thanks Tony, I appreciate your help. Look forward to hearing your results.
Johnny
Alright, here’s the verdict:
just like RG and Pixel said, An MP4 with 5.1 AC3 track is converted by the Live / Live+ / Live Hub into PCM.
I cannot tell by looking at my AVR exactly what TYPE, but sounds as if is 2-channel only. No surround. This would explain why your TV is having no problems with it.
This would also appear to be a BUG; The Live(x)'s should be outputting the raw AC3 track in an MP4. It’s probably been discussed before. I don’t recall because I don’t use MP4; 100% of my encodes are MKV.
An MKV with 5.1 AC3 track is sending raw Dolby Digital 5.1, with surround.
I don’t have the ability to make AVIs (and really don’t want to try anyway… 
) so I didn’t test that.
Do you have a Laptop or a PC near this TV that also has an HDMI or DVI port on the computer? If so, there’s a quick test that can be run to determine what your TV can do.
Wow, great work Tony, I really appreciate your help in sorting this out.
I also have the WD connected to Receiver, through the optical out. Confirmed that with mp4 files, the audio the WD is putting out to the Receiver is PCM 48, not AC3. The same Mp4 file puts out AC3 when played through another device (Tivo HD). So this is behavior by the WD in downconverting the AC3 file to PCM 2 channel, which is fine for playing over my TV, but it cripples the surround 5.1 for use in a real sound system. Not so good.
Regarding your quick test of the TV, I can connect the TV to a DVI computer port (not HDMI, don’t have that on the computer, would use a DVI to HDMI adapter. ) However, I’ve been poking around your other MANY helpful posts on this board, and found your post about your way to test a TV using the MonInfo program and a USB stick drive on the Hub. I did that, and lo and behold, under audio specs it only report capacity for PCM. So, unless the test you suggest is something else, I think this is sorted now. And I still think I want a new TV that WILL accept and play real AC3 files. (I was under the erroneous assumption that if a 2 speaker TV had a “tru-surround” feature it was processing 5.1 signal to get that … I guess it’s just some heavy reprocessing of two channel sound. )
So, I’m back to TV shopping I think. Anyone know a small TV that will do what I want, i.e. Play the AC3 stream from movie files???
Thanks again for your help Tony.
JohnnyLamb wrote:
So, I’m back to TV shopping I think. Anyone know a small TV that will do what I want, i.e. Play the AC3 stream from movie files???
I’m still a bit confused. Pretty much any TV will only have 2 speakers in it. It will only play a stereo mixdown. Some will pass 5.1 to a home theater receiver, but if the TV only has 2 speakers, why can’t you just send it a stereo stream, since you know it can play that? Why try to send it 5.1 and expect it to mix the 5.1 down to 2.0, when you can just send it the 2.0 it wants/needs?
Johnny: yep, that was the test suggested. Removed all doubt.
Hey Roofing Guy,
Yeah I hear what you’re saying but there is a reason and since you asked I’ll tell you.
I have the WD HUB connected, via an HDMI switch, to both the LCD TV and to a projector. They are in the same room. I use the projector for movies mostly, and use the TV for most everything else, but ALSO for movies or other shows that may have AC3 during the day when it may be too light or just when I don’t want to burn my projector lamp.
So …
I don’t want to use the receiver to do the sound when I’m using the TV (it’s not in the right place for surround to work right), and I don’t want to be switching the WD from stereo to digital repeatedly as I switch back and forth from Projector/AV Receiver system to TV.
By the way, Thanks for your input and your “guess” about the WD changing the ac3 to pcm in mp4 files was spot on.
