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Old Sep 14, 2010, 10:09 PM   #1
scotttaylor
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AppleTV HandBrake video playback choppy

All my Handbraked DVD's video playback choppy/stutter, audio is fine. I have a 160G AppleTV and have been trying various things to no avail. This is most noticeable while the scene is panning. It's very subtle but annoying. Every few seconds there's a small stutter in the playback. It seems to occur at random and replaying the same scene over and over it does not appear to stutter at the same spots each time. Every movie I've ripped with Handbrake shows the problem at some point. The audio is flawless. There are no discontinuities in the audio (5.1 pass through or 2 channel) at all. If I play the movies back via QT Player or directly within iTunes there's no problem. All movies play fine on an iPhone 4.0 and iPad...

My AppleTV is connected to my MacPro via Ethernet but I've tried direct wired, wireless, and syncing the movie before playback. All behave the same and exhibit the same choppy playback.

I've been using the latest release of Handbrake v0.9.4 x86_64 on a MacPro. I've also tried a most recent nightly build svn version 3525. I'm using the default AppleTV preset and I've tried using "Same as Source" for framerate as well as 23.976 fixed. All combinations show choppy video playback. Using the 3525 nightly build my advanced string is:

cabac=0:ref=2:me=umh:b-pyramid=none:b-adapt=2:weightb=0:trellis=0:weightp=0:vbv-maxrate=9500:vbv-bufsize=9500

Purchased or "Digital Edition" downloads DO NOT show the choppy playback so it really seems like this is a handbrake issue but other people do not seem to be complaining about it.

If purchased movies showed the same problem I'd say it seems like an AppleTV hardware problem but since they play fine it really seems like a HandBrake problem. Does anyone have any ideas...

Thanks,
Scott
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Old Sep 15, 2010, 04:29 AM   #2
Bufordt
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I've have the same type problem. How I solve it is to pause the video on the apple tv for about 10 sec. Gives the show time to buffer.
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Old Sep 15, 2010, 07:07 AM   #3
nwcs
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I've done the same thing when I see the aTV dropping frames. I pause for a few moments for it to fill the buffer. Works most of the time.
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Old Sep 15, 2010, 10:20 AM   #4
Yvan256
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My gusses would be a video bitrate problem, a video resolution problem or a PAL/NSTC problem.
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Old Sep 15, 2010, 10:46 AM   #5
rayward
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^^^

I get this with HB encodes from time to time, and it's always the bit rate causing the problem. Presuming that you use the Apple TV preset, try backing off the bit rate a couple of clicks and re-encoding. This typically does the trick but, if your movie has scenes with a ton of detail and movement, you may need to back it off even further. Trial and error is the only way to ensure you have the highest bit rate without stutter.
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Old Sep 16, 2010, 10:44 AM   #6
scotttaylor
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I think I figured it out!

Thanks for the input!

Constant framerate seems to be the answer. Even though I had previously tried setting the framerate to a constant 23.976 I was still seeing choppy playback. This time I tried 24 fps and that seems to have cured it. Not sure why setting to 23.976 didn't work? Maybe because that matched the source it behaved the same as setting "Same as Source"??? Are there any known issues to be aware of when transcoding into a different framerate than the source?

One comment regarding "buffering" of the stream. My observations have shown that when you pause a local network playback stream the network activity drops to zero - meaning there is no buffering going on when paused. I verified this by watching the network activity on my iTunes server using iStat Menus. It's possible an internet based stream continues to buffer if you're streaming from the iTunes store but I have not tested that case...
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Old Sep 16, 2010, 10:54 AM   #7
Yvan256
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Quote:
Originally Posted by scotttaylor View Post
Constant framerate seems to be the answer. Even though I had previously tried setting the framerate to a constant 23.976 I was still seeing choppy playback. This time I tried 24 fps and that seems to have cured it. Not sure why setting to 23.976 didn't work? Maybe because that matched the source it behaved the same as setting "Same as Source"??? Are there any known issues to be aware of when transcoding into a different framerate than the source?
Converting from one framerate to another is either dead simple (perfect multiple of one framerate to another, ex: 24 FPS down to 12 FPS) or problematic (film progressive 24 FPS to interlaced NTSC 29.97 FPS).

You usually don't want to convert the framerate at all. Let the hardware do any framerate conversion if necessary. Ex: An iPod touch doesn't care about interlaced or 29.97 FPS, but an old NSTC CRT TV will require it.

http://en.wikipedia.org/wiki/Frame_rate:

In short: you usually want to leave it at "Framerate: same as source" in 99.99% of cases. The other 0.001% is badly encoded DVDs, etc.
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Old Sep 17, 2010, 06:20 PM   #8
scotttaylor
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Quote:
Originally Posted by Yvan256 View Post
In short: you usually want to leave it at "Framerate: same as source" in 99.99% of cases. The other 0.001% is badly encoded DVDs, etc.
I hear what you're saying. That makes perfect sense and was the path I was on until I was derailed with choppy playback using "Same as Source" framerate setting.

I found this comment:

However, understand that DVDs and other MPEG-2 video streams use inherently variable framerates. This means that the actual framerate is not a steady number. This doesn't matter in most cases--for example, iPods handle it well. But if you find that playback is jerky, you might want to experiment by specifying a particular framerate instead of using "Same as source."


in the Handbrake FrameRate documentation today:
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Old Sep 17, 2010, 06:24 PM   #9
scotttaylor
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Whoops, hit submit before I was done...

So it appears the Handbrake team was aware of limitations in the AppleTV to play variable frame rate content. In conclusion: to avoid choppy playback you need to experiment. If you don't want to reduce quality from the default AppleTV setting RF=20, then using a constant framerate of 24 (for film) seems to be a reasonable tradeoff...
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