AC3 Audio Fun

[mvallevand]

In tonight's (0313) dongle, I thought I'd have some fun and so I enabled AC3 audio. It is only for fun because the audio and video are terribly out of sync but I thought someone might be interested in see what the mvpmc is capable of.

I actually only tested with VOB files in mvpmc native mode but it could work with emulation mode if the following conditions are valid

1. You have digital output on one of the newer revision H mvp's or you have mod'ed your older mvp, perhaps using jksmurf's execellent guide at this link

http://www.mvpmc.org/~stuart/HAUPPAGE_ME...ummary.pdf

2. the only audio stream in the file is AC3

3. GBPVR sends the mpeg file without transcoding

4. AC3 passthru is enabled via the Settings menu option or through the command line option -o passthru

I'd be curious getting feedback on this.

Martin

[mvallevand]

I forgot to mention that starting in the last alpha (0327) I have provided a way to manually sync the AC3 a/v when using either the pure AC3 pass through feed or the AC3 downmix to stereo on your tv or via the analog output. The keys are

* slow video by 1/100 of a second
# slow video by 1/1000 of a second

Note that I could set an option to downmix AC3 on analog to Dolby stereo instead of stereo, if anyone wants to try this.

Martin

[jksmurf]

I'm disappointed that no one cares about AC3, Martin

I don't think no one cares but:

1. Personally, I really don't know much about AC3. I'd hazard a guess a lot of other folks think the same. If you don't have DVB yet (like me) you won't be using it right?
   
2. I guess it only makes sense if you have a NEW MVP with SPDIF, so that cuts out an awful lot of users for a start?
   
3. I have read quite a few posts that it works but is "out-of-sync". So how can I test it for you? With a DVD?
   
4. Presumably I have to install an AC3 filter? Is there a recommended one? AC3Filter, DScaler, FFDShow? I understand that PowerDVD 7 does NOT have SPDIF output. I have (and use) Nvidia PureVideo Decoder which I understand has 5.1 but I get a problem with "Audio Decoder: NVIDIA Audio Decoder" as documented here.
   
5. Do you have to have a "grunty" PC for AC3, maybe not for AC3 itself, but the accompanying Video Codec / on the fly transcoding? If so, then maybe my PC is too pathetic to do this :o
   
6. Is this an issue? "But it is a big problem with SPDIF passthrough mode: most sound cards cannot work with 44100Hz SPDIF sample rate (used by AudioCD). Currently it is no workaround for this. The only solution possible is to resample audio from 44100Hz to 48000Hz. But this feature currently is only in plans."

Sorry for soooo many Q's!!

k.

[mvallevand]

I don't think no one cares but:
Do you have to have a "grunty" PC for AC3, maybe not for AC3 itself, but the accompanying Video Codec / on the fly transcoding? If so, then maybe my PC is

I've moved the post here because I want to try to keep everything together. For AC3 all the work is done by mvpmc so your server really isn't impacted other then the audio portion of the file is bigger and it pushes the server and the network a bit more, although nothing close to the size of the video though. Definitely no AC3 filter, or on the fly transcoding, or even sound card on the gbpvr server is necessary.

I guess the easiest way for you to test is with a VOB renamed to MPG. Note my second post for the keys to manually sync the a/v. I think will be able to sync these better but I'm going to need some DVB and ATSC samples.

Also this works for any emulation mode user. If passthru isn't available the AC3 is downmixed to stereo and as mentioned I could downmix to surround sound if that was prefered (or I could even add another command line option )

Martin

[jksmurf]

For AC3 all the work is done by mvpmc so your server really isn't impacted other then the audio portion of the file is bigger and it pushes the server and the network a bit more, although nothing close to the size of the video though.

Good news.

Definitely no AC3 filter, or on the fly transcoding, or even sound card on the gbpvr server is necessary.

Better news.

I guess the easiest way for you to test is with a VOB renamed to MPG. Note my second post for the keys to manually sync the a/v.

I'll try it tonight hopefully.
Q1. Is it still only the (0313) dongle?
Q2. My MVP is downstairs, my PC upstairs. My guess is MVP owners keep these seperate, otherwise they probably wouldn't have an MVP :-). My point is, that you'll have me running up and down the stairs to press the * and # keys ... so would a future test dongle be able to programme the remote keys instead e.g. Channel Up down or sth else? to make this test adjustment?
Q3. Is Video always faster than AC3 (you have no speed up video key...in case I go too far....)

I think will be able to sync these better but I'm going to need some DVB and ATSC samples.

Where can I get a DVB stream to test? There must be 100's folks here with a short clip :-) How about a donation ...

k.

[HtV]

My point is, that you'll have me running up and down the stairs to press the * and # keys ...

It's nice picture: Mrs on the sofa, JK running up and down the stairs...... You might skip the gym, might even save you some money, better not let mrs know.:eek:

[mvallevand]

Good news.
Better news.
I'll try it tonight hopefully.
Q1. Is it still only the (0313) dongle?
Q2. My MVP is downstairs, my PC upstairs. My guess is MVP owners keep these seperate, otherwise they probably wouldn't have an MVP :-). My point is, that you'll have me running up and down the stairs to press the * and # keys ... so would a future test dongle be able to programme the remote keys instead e.g. Channel Up down or sth else? to make this test adjustment?
Q3. Is Video always faster than AC3 (you have no speed up video key...in case I go too far....)

A1 - All since then, plus last night I built 0511 to mvpmc so it's all in the nightly now

A2 Funny, the keys are on the new remote. I haven't figured out how to do this logically on the old remotes.

A3. No but I've never seen it start the other way around however if you keep slowing down the video it will be slower than the audio.

Martin

[pz1]

A1 - All since then, plus last night I built 0511 to mvpmc so it's all in the nightly now

Martin,
What do you prefer us to test, the alpha or the nightly?
Pieter

[mvallevand]

Martin,
What do you prefer us to test, the alpha or the nightly?
Pieter

Right now there better be no difference. The nightly will be more static (not necessarily better) with 99.12 the alpha will no address future versions where I might have to get experimental again. I will keep the changelog.txt current.

Martin

[zehd]

3. GBPVR sends the mpeg file without transcoding

Martin,

You know, I haven't really played much with this, but it might be time. Would you say that you don't want on- the- fly transcoding, because the transcoder may drop the multichannel sound, or downmix it?

From my perspective I would want to see ZProcess work with mvpmc, but haven't really tried yet. I have built 6 channel sound into ZProcess but haven't been able to use it yet because of the MVP being 2 channel only , til now...

I'll check through your sub-forum a bit more and see...