Ocaisional Stutter in ATV Video Playback
#1
Hi all,

I'm getting a stutter in video playback on my Apple TV running 8.10bf1 (ATV 2.2). It is very subtle (but enough to drive me loopy) and happens every 10 seconds or so. It is most evident in HD mp4/mkv files, I cannot say for sure it is exclusive to HD content but it's definitely more pronounced. I've gone to considerable lengths to ensure the encoding method was something ATV could handle, using different programs, etc so I don't think it's that. Additionally a sample file run locally through ATVfiles ran just fine.

I am playing these files from a Window's share over a powerline adapter. Speed has never been an issue.

Some settings.
I have upscaling disabled
VSync enabled
Rendering Method: tried all 3, no change
CPU Usage during playback is between 40-60% depending on file

Handbrake Encoded Video File Stats.
Video
Format : AVC
Format/Info : Advanced Video Codec
Format profile : [email protected]
Format settings, CABAC : No
Format settings, ReFrames : 3 frames
Muxing mode : Container [email protected]
Codec ID : V_MPEG4/ISO/AVC
Duration : 3h 12mn
Width : 960 pixels
Height : 384 pixels
Display aspect ratio : 2.445
Frame rate : 25.000 fps
Resolution : 24 bits
Colorimetry : 4:2:0
Scan type : Progressive
Writing library : x264 core 65
Encoding settings : cabac=0 / ref=3 / deblock=1:0:0 / analyse=0x1:0x131 / me=umh / subme=7 / psy_rd=1.0:0.0 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=0 / 8x8dct=0 / cqm=0 / deadzone=21,11 / chroma_qp_offset=-2 / threads=6 / nr=0 / decimate=1 / mbaff=0 / bframes=6 / b_pyramid=0 / b_adapt=1 / b_bias=0 / direct=3 / wpredb=1 / keyint=250 / keyint_min=25 / scenecut=40(pre) / rc=crf / crf=20.9 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.40 / pb_ratio=1.30 / aq=1:1.00

Audio
Format : AAC
Format/Info : Advanced Audio Codec
Format version : Version 4
Format profile : LC
Format settings, SBR : No
Codec ID : A_AAC
Duration : 3h 12mn
Channel(s) : 2 channels
Channel positions : L R
Sampling rate : 48.0 KHz
Resolution : 16 bits
Language : English


I wouldn't mind spending the extra money for a full fledged HTPC but I don't want to do it if system power is not my problem.

Thanks a bunch
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#2
25.000 fps video content on a 60Hz display maybe?
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#3
I believe my set is 120Hz. It's a Sony KDS-60A3000. I really don't know anything about re-encoding. Does the framerate have to match the source? Can it be changed? Also, samples seem to play fine locally on ATVfiles. I guess one thing I can try is playing the file locally through XBMC just so I can eliminate the network as a possible culprit.

Edit: Checked some of my other files, 23.976fps files have the same stutter. :\
The overall experience is still amazing and I guess I shouldn't complain but the perfectionist in me is going nuts.
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#4
I have the 55 inch version of that set and experience all of the same issues with 24fps content. I think with the newer faster refresh TVs it's far more noticable than the older ones.

Essentially it appears as though XBMC (and subsequently boxee) doesn't do any standard frame rate conversion (2:3 pulldown) when displaying 24fps material at 60hz. The default resolution of the appleTV is 720p at 60hz (it'll support 1080i and 1080p at 60hz or 50hz for PAL). It will not allow outputting of 1080p/24hz (which that Sony TV will support).

ATVFiles uses quicktime for playback which does a proper 2:3 pulldown (inserting extra frames to smooth playback) so the video looks nice and smooth. DVD players, Blu-Ray players, HTPCs, dedicated streaming boxes, even most media players on PCs do proper framerate conversion to help with this problem. I believe this should be considered a requirement for XBMC, and hope one of the developers gets the motivation to work on it.

The product is fantastic, but that alone is enough to keep me bouncing in and out of XBMC to frontrow for playback of movies.
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#5
Perhaps, but if that is what I am seeing, wouldn't I definitely see it on all video formats? It seems I do not see it on lower quality xvid files. DVD ISOs also seem to play ok. Additionally, I never had this issue on XBMC for the XBOX with the same TV.

Frustration!
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#6
"I never had this issue on XBMC for the XBOX with the same TV" -> the XBMC on XBOX can change the display framerate and resolution depending on the video content. XBMC for Mac does not work the same way.

As far as I know, there is no pulldown going on with XBMC code. So 24/25/50 fps video content on 60Hz displays will have a slight framerate miss-match. It does not look like a stutter but it's a slight tear in the video content.

120Hz TVs do an internal framerate adjustment, they are still 50/60Hz inputs.

I would find some 30 or 60 fps video content and try that to see if you are seeing the same artifact. If it looks good with no periodic stutter, then it's a video content framerate conversion issue.
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#7
I have done tests with 30fps videotape based video and it does not suffer from the same "stutter" look that I get with 24fps film based video. Unfortunately more and more TV video is being shot on film or with HD cameras which shoot in 24fps to mimick the film look. Almost any new TV show seems to be in 24fps on DVDs so the problem is very prevalent.

I am sort of curious why this isn't a bigger deal to people on this and other forums. It annoys me enough to switch out of XBMC whenever I want to watch a movie... Not quite what I want to have to do.
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#8
dan1son Wrote:I have done tests with 30fps videotape based video and it does not suffer from the same "stutter" look that I get with 24fps film based video. Unfortunately more and more TV video is being shot on film or with HD cameras which shoot in 24fps to mimick the film look. Almost any new TV show seems to be in 24fps on DVDs so the problem is very prevalent.

I am sort of curious why this isn't a bigger deal to people on this and other forums. It annoys me enough to switch out of XBMC whenever I want to watch a movie... Not quite what I want to have to do.

Might be a display difference. My WestingHouse LCD HDTV seems to be very good at being insensitive to framerate issues. I never notice them.
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#9
davilla Wrote:Might be a display difference. My WestingHouse LCD HDTV seems to be very good at being insensitive to framerate issues. I never notice them.

That could very well be the case. The SXRD TV I have seems to have an amazing response time. It has a "motion enhancer" which works by implanting black or grey (depending on the mode) frames in between the proper frames to give it more of a film look. This makes the picture appear darker but when waving my hand in front of the screen you can clearly see the screen does get amazingly dark in between frames. I have this turned off since it only makes the stuttering worse.

I have tried every combination of their motion enhancers and, while some help, it's still obnoxious on panning scenes.

I'm guessing since the developers don't notice the problem much... it's not on the radar for being worked on.

What library does XBMC use for decoding/displaying H.264 content on OSX?
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#10
dan1son Wrote:That could very well be the case. The SXRD TV I have seems to have an amazing response time. It has a "motion enhancer" which works by implanting black or grey (depending on the mode) frames in between the proper frames to give it more of a film look. This makes the picture appear darker but when waving my hand in front of the screen you can clearly see the screen does get amazingly dark in between frames. I have this turned off since it only makes the stuttering worse.

I have tried every combination of their motion enhancers and, while some help, it's still obnoxious on panning scenes.

I'm guessing since the developers don't notice the problem much... it's not on the radar for being worked on.

What library does XBMC use for decoding/displaying H.264 content on OSX?

The display resolution and 24/25/50/60 framerate issues are on the radar but it's not going to be solved tomorrow.

XBMC uses ffmpeg for h.264 decode. Display is handled using OpenGL.

XBMC for Mac uses both Cocoa and SDL routines for display handling.
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#11
Does XMBC for Windows and XBMC for Linux have this same limitation? or are they more like the XBOX version?
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#12
gferrazzano Wrote:Does XBMC for Windows and XBMC for Linux have this same limitation? or are they more like the XBOX version?

Sorry, You would have to ask in the platform specific forum areas. My specialty is OSX/AppleTV.
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#13
I found a pretty large thread on the topic in the Windows forum.

While they're is no solution yet, it feels good to at least know what the problem is. Thanks for answering my questions davilla.
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