Capturing digital audio stream from TV

[prdaniels]

Hi there,

Long time reader, first time questioner here.

Basically, what I'm wanting to do is to stream a concert through my TV in 4K (for the best audio) and somehow route the audio to my computer so that I can capture/record it. My goal is to then use this audio to make my own album for future listening so that I don't have to always stream the full A/V concert. Your advice is needed!

My TV is a 4K/UHD LG smart TV, and has digital optical output as well as HDMI ARC and the usual RCA connections. The A/V data stream is coming into the TV from an Apple TV 4K unit via HDMI.

My computer is a Dell XPS 15 9560 and lists the following sound cards listed in Speccy:
- Intel Display Audio
- NVIDIA Virtual Audio Device (Wave Extensible) (WDM)
- Realtek Audio

As far as the recording software goes, I had thought to use Audacity's 'record' function as it seems like a fairly straightforward setup.
My intention is to see if I can capture the unbroken digital audio signal in the easiest way possible - but reading around on the different forums, unfortunately I could not see a way to do this. I understand that one complication is that the digital streams are encrypted (is this the case?) or have some form of DRM which prevents 'capturing' them digitally.

I had a few ideas on where to begin in terms of the recording setup:
- TV => HDMI ARC => Computer
- TV => HDMI ARC => USB adaptor => Computer
- TV => Digital optical cable => HDMI adaptor => Computer
- TV => Digital optical cable => USB adaptor => Computer
- TV => Digital coax cable => M-Audio Audiophile 2496 PCI Digital Audio Card => ? => Computer

I also know that there are external sound cards that can convert from digital to analogue, which could then feed into my computer - but my worry is about the fidelity loss in converting from digital to analogue to digital again. I'm happy to be corrected as to whether this is actually an issue. I've also suggested above using the M-Audio Audiophile 2496 PCI Digital Audio Card as it has digital pass through. But I appreciate that another card might be a better fit for what I'm trying to do here.

Has anyone here had success with their own setup? Is there anything here I'm missing or which is technologically not possible due to incompatible parts of the path? Or is there something I'm not understanding about the way the digital transmission works?

Any help or guidance appreciated. As are links to another post which offered a successful solution (as said above, I couldn't find anything over a number of google searches).

With thanks in advance,

Paul.

 

[NiHaoMike]

The only way I can think of (for the full quality) is to take a HDMI audio extractor that supports surround, then tap off the digital I2S signals just before the DAC using a FPGA board or similar. It would take quite a bit of electronics knowledge, but not that difficult compared to a lot of other things hobbyists have done.

I'm not aware of anything that accepts HDMI ARC and gives you something that plugs into a PC. S/PDIF (coax or fiber) only supports stereo uncompressed, so surround comes at a quality loss.

 

[bmwbaxter]

Why not just use a 4k capture card.

Streaming device ---> Capture Card (PC) ---> TV

Once it is recorded on the PC you can just re-encode as an audio file from the 4k capture. Since it is directly capturing the stream you should be able to get the full audio quality.

EDIT: Yarr Matey

 

[NiHaoMike]

Most capture cards will not accept a HDCP signal, so then you'll also need a way to strip HDCP. Also, I don't think they support surround since cameras do not output surround over HDMI - in professional settings, surround sound is captured by a dedicated setup.

 

[bmwbaxter]

Hmm... I guess the CP in HDCP is the issue.

 

[habbajabba]

You need to capture the output from the tv (to your speakers). Once the signal leaves the tv it's no longer encrypted or otherwise separate speakers (what I use) would not work. My tv's speakers have never been used ever. I use an rca (right and left signal) to 3.5mm single jack 15' cable from monoprice direct to the back of my left A5+ speaker. You could split the 3.5mm stereo output end and send it to a digital recorder?. I only have a 2.1 setup so any 5.1/7.1 audio signals are reduced to 2.1. OTH, there are softwares that can record whatever your pc is doing, even the spdif output. So if you bought this software you would essentially be able to record whatever you want, video and audio.
You would have to search yourself. I did it once and don't recall any names offhand.

 

[Zerileous]

You need to capture the output from the tv (to your speakers). Once the signal leaves the tv it's no longer encrypted or otherwise separate speakers (what I use) would not work. My tv's speakers have never been used ever. I use an rca (right and left signal) to 3.5mm single jack 15' cable from monoprice direct to the back of my left A5+ speaker. You could split the 3.5mm stereo output end and send it to a digital recorder?. I only have a 2.1 setup so any 5.1/7.1 audio signals are reduced to 2.1. OTH, there are softwares that can record whatever your pc is doing, even the spdif output. So if you bought this software you would essentially be able to record whatever you want, video and audio.
You would have to search yourself. I did it once and don't recall any names offhand.

True, it's no longer encrypted but it is also no longer digital.

....
My intention is to see if I can capture the unbroken digital audio signal in the easiest way possible....

 

[freakdiablo]

Some PCIe cards do have optical audio input, just use the output from the TV. That way you don't have to screw around with HDCP, going from Digital>Analog>Digital, cats and dogs living together, or any of that fun jazz.

First one I found.

Edit: Sorry if this was already answered - do you want surround or just doing stereo? Just because optical audio does have some compression when it comes to surround. Thought I'd throw that out there as wanting to keep it digital may imply you want to lose as little fidelity as possible.

 

[habbajabba]

B&H has a Hauppauge HD Personal Video Recorder 2 for $139 backordered. It accepts hdmi & spdif input.
https://www.bhphotovideo.com/c/product/925432-REG/hauppauge_1512_hd_pvr_2_video.html/specs
Or there is a $400 ($500! 2months later) Tascam DR-701D 4-Channel / 6-Track Multitrack Field Recorder which has both hdmi input and output.
https://www.bhphotovideo.com/c/product/1189478-REG/tascam_dr_701d_linear_pcm_recorder.html/specs
You're in luck, it's in stock lol.
Apparently, simple and inexpensive digital recorders with an spdif input are non-existent. More bs brought to you by the retards who restrict electronics here in the US. Amazon has a cheap spdif splitter (https://www.amazon.com/dp/B073S7MK9D?tag=duckduckgo-d-20&linkCode=osi&th=1&psc=1) but no one makes a cheap recorder with other than 3.5 mm jacks? Ridiculous as this is too simple.
I would look into plugging the apple direct to pc and simply using software to record the audio only. Or the hauppage with a splitter. ??
I know for a fact that devices are made than can capture any input for any reason but again, the miscreants who restrict devices based on geography are the real problem. Region coded dvd players to name the obvious.
Even if all you did was capture the entire video it would be too easy to split the audio track out with free software. MKVToolnix is my goto for anything video.
A buddy of mine used to have a home studio and he would use a vcr to record the audio. He was on a budget for sure.

If the stream is encoded you will require a device that decodes it as well in order to record it trough the spdif and no doubt the hdmi as well. Some guy said he was forced to use the component outs because of the drm encodings. If this is a tv concert stream no doubt it will be drm'd.
One way encryption, how sweet it isn't.