Choosing a reclock strategy

[marcdbl]

I am trying to figure out the best way to deal with smooth video playback on my HTPC.

The basic setup is this:
Plasma TV: connected via HDMI, accepts 1080 at 50i/60i/50p/60p/24p.
DTS/Dolby 5.1 Amplifier: accepts SPDIF.
HTPC: SPDIF soundcard, ATI HD3200 (catalyst 8.9), HDMI out.

I understand I can use reclock to lock the video player and video card refresh rates. And I can also use reclock to detect the framerate of a video-file and change the videocard refreshrate to something similar accordingly, using a script.

Usually I use a refresh rate of 50Hz, since I live in the UK, so the TV I record and playback is at 25fps. No problems here. However, sometimes I play a movie with a framerate of 24/23.976 fps. This actually looks ok at a refresh rate of 50Hz which surprises me. When I change to 24Hz, it gets a bit jerky, this surprises me more.

So I installed reclock, to see if that would help. It solved the problem of the constant jerkiness at 24Hz, but I seem to get dropped frames every few minutes. And this seemed to be true for PAL footage played at 50Hz too!

Clearly I need to work on this more, maybe I need to start cooking up some new refresh rates with powerstrip?

Given the capabilities of my setup (full choice of refresh rates, but I must use SPDIF), what would you guys suggest I do to get smooth playback with minimal sound-degredation. (Please note that for the time being, new hardware is NOT an option )

I realise it's my first post, so I might be asking a bit much, but any help much appreciated - I've got so much working with my HTPC but this is making my head spin!

 

[Jong]

If you are sending AC3/DTS to Reclock it has a difficult job. If the refresh rate you have set for your TV/monitor does not EXACTLY match a multiple of the rate of the video being played it cannot alter the speed of the audio it can only drop/repeat AUDIO packets to keep things in sync. I suspect that is what you mean when you say it is "dropping frames". The video should still be smooth, but if there are too many audio packets being dropped you will hear it in the soundtrack.

It is very common that the standard timings provided by your video card are not exactly correct, even for 50Hz, but they are likely to be so close you will not notice. However, if you want to be a purist (like many of us here) you can use Powerstrip to adjust your video timings so you do get EXACTLY 50.000Hz shown IN RECLOCK when playing your video. It has to be right in RECLOCK not in CCC and not in Powerstrip (unless you use the Powerstrip "camera" to measure the rate on the fly).

For "24p" material things are worse. The rate you actually want is not 24Hz at all but 23.976Hz or, alternatively if your TV does not accept "24p", two times that = 47.952Hz and again the rate has to be spot on if you are sending Reclock AC3/DTS.

You may have a further problem with "24p" material. Many PAL TVs cannot actually display at 23.976/47.952Hz even if they accept the signal. Instead they repeat frames to re-rate the video to 50Hz. This introduces judder at the TV, even if Reclock is solidly green with no dropped frames. If you notice any judder @23.976/47.952 you will need to use Reclock to re-time the video to 50Hz. To do this you will need to decode at least your 24p material so Reclock sees multi-channel PCM not AC3/DTS. Then Reclock can speed up the audio to stay in sync with the video. It can also reduce the pitch of the audio to compensate for the "chipmunk" effect, if that bothers you. However, as we have been watching PAL DVDs and US TV shows re-rated to 50Hz for TV broadcast for years often this does not bother people, in the same way that many Americans do not notice 3:2 pulldown judder.

The very latest Reclock beta is your friend if you choose to speed up 24p to 50Hz as it can re-encode the audio back to AC3 (at full bitrate, significantly better than DVD standard) after making its adjustments. Some here would argue that you should do this anyway as Reclock is "not good at handling AC3/DTS". However, I believe this is only true if you do not adjust your refresh rates to be spot on the desired rate. In my experience at least, if you do this Reclock works fine with AC3/DTS.

Finally, you will find that getting perfectly smooth video playback over a full movie duration on an HTPC is more of an art that a science. You can find that any number of background processes can jump in over a 2 hour period and briefly glitch your playback. Things like background AV scanners or OS firewalls are common culprits. If you get Reclock to where it is doing things perfectly AND you are sure your TV is not introducing 24p judder AND you still get glitches every few minutes you will need to look at all processes on your PC and progressively eliminate the cause.

 

[kaotech]

How did you set up reclock to use ac3converter with a stereo source ?

 

[marcdbl]

Thanks very much for this Jong, this is one of the best explanations I have seen.

It sounds like the best way for me to get started is to start using powerstrip to tune-in refresh rates of 50 and 23.967 exactly (as reported by reclock). Provided that my TV will accept these refresh rates without doing any compensation, I should then get smooth playback with zero dropped audio frames (ignoring all other factors for the time being).

Does this sound right, at least as a starting point?

 

[Jong]

How did you set up reclock to use ac3converter with a stereo source ?

Sorry, I did not understand this. What are you trying to achieve?

 

[Jong]

Thanks very much for this Jong, this is one of the best explanations I have seen.

It sounds like the best way for me to get started is to start using Powerstrip to tune-in refresh rates of 50 and 23.967 exactly (as reported by Reclock). Provided that my TV will accept these refresh rates without doing any compensation, I should then get smooth playback with zero dropped audio frames (ignoring all other factors for the time being).

Does this sound right, at least as a starting point?

Well I am torn. Personally I do believe you will get the very best results if your timings are spot on. As I mentioned about TVs repeating frames when fed 48Hz, I suspect many will silently drop/repeat frames if they are not fed exactly 50Hz or 23.976Hz or 59.940Hz. Then again, maybe they are not perfectly calibrated so will do this if the rate is not exactly 50.00xHz, for example, where x is dependent on your TV so unknown!

What you suggest is a good "purist" approach, the one I took!

An alternative, potentially much less painful approach, is to ignore tiny numbers of dropped packets reported in Reclock and say "does playback (audio and video) appear perfect and smooth to you"? If it does, STOP RIGHT THERE!

If it does not, is the problem audio ("pops" or similar) or video (judder).

If the problem is audio the quick approach is just to use your DVD playback software or AC3Filter to decode the audio to PCM and then use Reclock to re-encode it. Personally I hate unnecessarily decoding and re-encoding and as I now have perfect refresh rates I choose to still pass AC3/DTS for DVDs, but if you want to do that and you can hear audio problems at the moment you will need to go the Powerstrip route.

If the problem is video judder then, yes I would start by getting your refresh rates spot on. Try 50Hz for "24p" material if that still does not fix it.

Also look at eliminating processes if you have intermittent, or longer interval video judder, e.g. every 20 mins?

As I said, more an art than a science!

 

[kaotech]

Sorry, I did not understand this. What are you trying to achieve?

I try to convert stéreo channel to 5.1 channel like "DTS Connect" or "NEO :6", with the new fontion "AC3 encoding". But i don't know how to config that in Reclock.

 

[James]

I try to convert stéreo channel to 5.1 channel like "DTS Connect" or "NEO :6", with the new fontion "AC3 encoding". But i don't know how to config that in Reclock.

I am not sure why you want to do this, but just enable "AC3 encoding" as PCM output. Beware, the source must have a sample rate of 48kHz.

 

[James]

I try to convert stéreo channel to 5.1 channel like "DTS Connect" or "NEO :6", with the new fontion "AC3 encoding". But i don't know how to config that in Reclock.

If you want "surround expansion" - your surround receiver/amplifier will/should do this.

 

[Jong]

I don't think James has any plans to "upmix" stereo to 5.1 channels. At the moment he simply encodes any 2-channel PCM source to 2-channel AC3. Your amp can probably then do the upmixing if you desire it.

Edit: oops. We overlapped!

 

[kaotech]

Yup, several Motherboards, sound card or any amp can make this. But, i haven't this option and i don"t use pre-amp, just a sound card and a 7 channels amplifier. My pre-amp it's my HTPC

I'm looking for any software can make upmix (stéréo to 5.1)

 

[marcdbl]

I'm looking for any software can make upmix (stéréo to 5.1)

Ac3filter can do this.

 

[Jong]

Yes, good tip.

Just make sure AC3Filter is set to process PCM, then set output as "3/2+SW 5.1channels" and make sure "Use s/pdif" is NOT ticked.

 

[Mark_A_W]

If you are sending AC3/DTS to Reclock it has a difficult job. If the refresh rate you have set for your TV/monitor does not EXACTLY match a multiple of the rate of the video being played it cannot alter the speed of the audio it can only drop/repeat AUDIO packets to keep things in sync. I suspect that is what you mean when you say it is "dropping frames". The video should still be smooth, but if there are too many audio packets being dropped you will hear it in the soundtrack.

I read this completely differently. I think he means the VIDEO is dropping frames.



And if you do manage an accurate timing with Powerstrip, then Reclock works really well with AC3 passthrough. You might get one or two dropped/repeated AC3 packets per hour, which is COMPLETELY inaudible.

Before Hi-Res audio came with BD/HD-DVD I ran SPDIF for this reason.


Now Reclock has an AC3 encoder, but if you can it's better to stick with Analogue or HDMI out for Hi-Res audio. (The OP can't though).

 

[Jong]

I read this completely differently. I think he means the VIDEO is dropping frames.

I confess I wasn't sure. However, a lot get confused by the Reclock properties page talking of "drops" and "repeats" when using AC3. However, if it was visible video judder, with Reclock doing its job that should be due to either other processes running or his TV repeating frames both of which are covered later in the post.

And if you do manage an accurate timing with Powerstrip, then Reclock works really well with AC3 passthrough. You might get one or two dropped/repeated AC3 packets per hour, which is COMPLETELY inaudible.

That is exactly what I say in my post.