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Capturing AC3 audio from Sky+

Discussion in 'Desktop & Laptop Computers Forum' started by Steve1138, Jun 15, 2003.

  1. Steve1138

    Steve1138
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    Now there are more widescreen + DD AC3 film channels on Sky, I'll be wanting to capture & store more films on DVD.
    Haven't tried it yet (still fairly new to it) but wondered if there's anything special you need to do to be able to record the AC3 audio.

    My capture work so far has been from prog's on other non-AC3 channels, but I did use the optical audio off the Sky+ into my Terratec sound card (with optical I & O)and recording the 48 kHz PCM stream.

    Have used Virtual Dub for capturing at 352 x 288 and AmCap for larger resolutions. (VD won't work @ > 352x288 with my non-8x8 capt.cards). Also just started using the all-new version of VirtualDubMod with its great AC3, MPG, VOB support.

    Do you expect that a sound card with digital in & out to just pass the AC3 straight through, or is a special card needed ?

    Are any special capture prog's needed to be able to capture the AC3 track audio input ?

    cheers m8t's
    Steve
     
  2. Rob.Screene

    Rob.Screene
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    Hi Steve,
    Yes I've done it with a 2496 off laserdisc AC-3. There is a detail thread about it on avsforums.com, search for laserdisc and ac-3 and capture, that should do it.

    regards,
    Rob.
     
  3. Steve1138

    Steve1138
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    couldn't find the thread on AVSforums (trouble with that forum is there's more traffic on it in a day than there is here in a week... so it's difficult to find stuff)

    anyone else ?
    how to capture the AC3 stream direct from Sky+ optical audio OUT >> sound card opt.IN ?

    looked in the new VirtualDubMod AUDIO settings and couldn't figure anything out from there ?

    Steve
     
  4. Rob.Screene

    Rob.Screene
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  5. Steve1138

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    Gooood grieeeff !!!!

    ..and your reply was so casual, like !!
    "Hi Steve,
    I think this was the thread..."

    you didn't say it would be THAT hard / technical (or that you wrote half of it !. I'm very impressed, but if THAT's what it takes at the mo to grab AC3... then I won't even attempt it from my Sky+ box until something comes along where you can pick it from a menu in VirtualDub (etc)...
    I'll continue using the PCM audio from the optical out at the moment I think.

    Maybe nobody's fixed this "problem" yet (in a simple way), as AC-3 is normally only found on DVD and you would copy / rip DVD's internally in yr PC - so no need to solve the "problem" of grabbing AC-3 from an external device (...other than LD's and digital sat receivers... )
    ...but I wish somebody WOULD.
    Maybe have to throw down the gauntlet on Doom9 ? and see if anyone throws in the towel ?!

    Thanks again
    Steve
    (disappointed)
     
  6. Xeonic

    Xeonic
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    Ok, ok, I'll put you out of your misery ;)

    It is possible, and yes it is a bit of work....

    One of the biggest problems is that you need to find a soundcard that can transfer the signal bit for bit, unchanged. I already have a SB card which can't do this, but found out that cards based on the cmedia 8738 chip *might*. So I got this trust one from dabs. It's about 30 quid, and is good value since it has analogue 5.1 out, as well as both coax/optical in and out!

    Next was the digital recorder, I think the same one mentioned in the thread rob referenced. In theory any wav recorder, like the built in windows one should work, if the stream is unaltered.

    Set it to 16 bit, PC format, start the 5.1 signal and press record, that's it!

    This gives you an ac3 file - and the start of the hard work :) To sync it with a video captured elsewhere is pure guess work, but an app called "ac3 delay corrector" can be used to cut a few frames. The almost laughable method I used for padding out was to have a very short "silence" ac3 file (say 0.5 second) , and use dos copy to add to the start of the main one!! :laugh:

    In the end you have two files which can be muxed together and then burnt to dvd or whatever. Yes it's hard work, but the ability to make 5.1 dvds is pretty cool :p
     
  7. Steve1138

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    Xeonic - okay, thanks

    I intentionally bought a card already with optical I/O for this purpose, thinking that any card with a digital audio I/O would pass the stream through to the capture programme unaltered (as you say, bit for bit), whether it be PCM or AC-3 (in my case - both from my Sky+)...

    I bought the TERRATEC Aureon 5.1 Fun and have used it successfully to capture PCM from Sky+ with the optical in.
    I didn't expect it would be 'monkeying around' with the signal, but just pass it straight through the bus...

    The TRUST card looks like a good option as it has both optical and co-ax (mine has optical only) although I don't need the 5.1 decoding as I have a LEXICON DC-1 surround processor at the heart of my system (which is where this PC will be).
    Come to think of it - I haven't actually tried to capt. any AC-3 yet... but if you hve the TRUST 5.1 card, and I have this TERATEC 5.1 card... then maybe mine will work already.

    Did you mean the Windows Sound Recorder (from the Accessories > Entertainment menu ?).
    I looked in File > Properties > Convert Now, and you get the same box as you see when selecting the audio format from say VirtualDub, but it's not clear to me what to set it to from your first note (PC and 16 bit) or did U mean PCM ?

    or do I need to load any extra codecs / filters to handle the AC-3 input ?

    HELP (again !) thanks
    Steve
     
  8. Xeonic

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    Actually I saw the aureon but didn't know if the 5.1 model could do the "non-audio" mode needed for ac3 - hope it does!

    The recorder and settings I referred to was the one noted part way down the avs link - ac3 digital recorder or something like that. Since it seems to be an old version, a simpler way would be a straight 48k 16bit raw file with any wave recorder and change the extension, but I've yet to try that.

    You don't need filters to save the ac3, at least using the trust, as it is not actually decoding - it sounds like static, but luckily you don't have to monitor it! To listen to what you saved properly, any modern software dvd player should work.

    Reading that thread some more I think Rob's got the audio/video syncing more sussed than me :cool:
     
  9. Rob.Screene

    Rob.Screene
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    Hi Steve,
    I think it's a good idea to wait for it to become mainstream within the next 6 months.

    I had my anorak on then when in those days! There was so much myth that it could not be done, that I took the time to document how I did it.

    For me it was a labour of love and I had some spare time. I wanted my PAL Star Wars Laserdisc picture quality with the 5.1 sound off the NTSC ones, as widescreen anamorphic 5.1 DVD's that I wouldn't have to change discs on at the back of my dark HT room.

    I really miss the convenience of Laserdiscs, not!

    Ian, I found it was much easier to insert and crop black frames at the start than to dare try to edit the AC-3 bitstream! 1 frame at 23.976fps gives +/- 41.7ms granularity which was close enough for my eyes.

    cheers,
    Rob.
     
  10. Steve1138

    Steve1138
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    well - waddya know ?!!
    (Xeonic..)
    Now I've just pulled my TERRATEC sound card out from the Home PC ready to install in the new HCPC and it also has the C-media 8738 chip !!

    I'll have to now give it a try like you suggested

    Steve
     
  11. Madders

    Madders
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    This may be slightly off topic, but how can you play an AC3 signal direct from the Sky+ box, decoding the signal in your HTPC and sending the decoded analogue signal to the amp? I have an RME soundcard so have the digital in and analogue outs.

    Look forward to suggestions...

    Cheers,

    Steve
     
  12. Xeonic

    Xeonic
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    Steve1138
    The SPDIF settings were only on the cmedia mixer, not the windows one, so interesting to know if you can do this with the terratec...

    SteveNOT1138(!)
    There's a recent thread on the us avsforums about this very matter, AC3 into a PC using WinDVD 5. If that problem's solved, can throw the receiver away :)
     
  13. Madders

    Madders
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    Thanks for the reply Ian. I have been reading this thread with interest, however as I have no experience in writing code/filters, I couldn't figure out how to get it to work!:confused: :rolleyes:

    Any suggestions in leymans terms would be highly appreciated :clap:

    Thanks,

    Steve
     
  14. Xeonic

    Xeonic
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    Steve

    This directshow filter page has a link to a direct show utility which includes a html readme which is a pretty good introduction and description of filters. If you read that you'll see no coding is involved, just literally dragging lines from one filter block to another :)

    Besides that, if you go to the online microsoft knowledgebase and search for "graphedit" you'll find more info there.
     

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