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hafr · (This post was last modified: 2011-11-15, 00:29 by hafr.)

I was gonna watch the latest episode of The Amazing Race today, an x264 720p rip. The Amazing Race S19E08 720p HDTV X264-DIMENSION, 1,7 GB and 42 minutes. There was no problem watching it on the computer, but when streaming it to the ATV2, the video was way slower than the sound.

No "choppiness" in the playback of the video or the sound, and other films with higher bitrate were working just fine. I decided not to bother and just got a regular SD rip to watch instead and deleted the HD one. It was the same when it was rar'ed as when it was unpacked and playing the .mkv.

But now it's bugging me. Why did this happen? Has this happened to anyone else, and is it a known "thing"?
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After some consulting with Mr. Google, I've found out that the rip is in 60 fps, and that ATV2+XBMC just won't play 60 fps in 720p...

That sucks, because I really like the smoothness in 60 fps rips...

mcpish · (This post was last modified: 2011-11-16, 06:29 by mcpish.)

The rip of the episode you got was probably taken taken from a 720p60 source and encoded at 60 frames/second. You can use something like mediainfo to find out for sure.

I've noticed this problem with videos that are recorded at 60 fps (frames/second); The AppleTV can't handle them. It can only do either 24 fps recordings (telecined) or deinterlaced 30 fps, not hi-motion 60 fps. What's happening is that the AppleTV ends up playing your 60fps video at 30fps, hence it's running at 1/2 the speed.

It's a known hardware limitation of the AppleTV2. It's the same reason why you can't get good hi-motion (bob) deinterlacing working with the mythbox plugin under xbmc either. So if you record something off a channel that broadcasts in 720p60 (both ESPN and ABC do this, plus CBC in Canada), you must also reduce the framerate from 60 to 30 when you transcode. (59.94 to 29.97 to be exact). Most other channels broadcast in 1080i30 which most show-cappers end up using some sort of "field combination" de-interlacer. This process effectively halves the temporal resolution of a 1080i30 recording from a 60Hz refresh rate (60 unique fields) to a 30Hz rate (30 unique frames). You end up with a choppier video than true "live broadcast tv", however the result is compatible with the AppleTV. When cappers record from a 720p60 channel like ESPN or ABC, they don't need to bother deinterlacing so they just keep the native 60 fps frame rate (which causes problems for AppleTV). If most cappers used a "field extension" deinterlacer instead of a "field combination" deinterlacer and preserved the 60Hz hi-motion signal when recording a 1080i30 channel, you'd see this problem a lot more.

hafr · 2011-11-16, 11:29

It's a known hardware limitation? That sounds a bit strange, I must say. I used the passthrough option (keeping the video intact) in iVI to get in to an iTunes friendly format, added it in iTunes and the ATV2 played it flawlessly, but XBMC still played it as if the video was 24 or 30 fps.

And when googling around, there are people posting logs of the same problem, and it seems to be XBMC misinterpreting something and playing it in 24 or 30 fps instead of 60, making the video "slower" than the sound.

mcpish · (This post was last modified: 2011-11-16, 21:12 by mcpish.)

hafr: yes it's a hardware limitation. The AppleTV simply cannot play 60 frame/sec video files. There's nothing wrong with the file (they play fine on PC) but you can't play them properly on the AppleTV. As I said, the AppleTV will play back a 60 frame/sec file at 30 frames/sec, therefore it will appear to run at 1/2 speed (ie. it takes 2 seconds to display that should be displayed in 1 second).

hafr · 2011-11-16, 21:28

So why is the same file playing back perfectly in the standard ATV2 GUI?

The Apple TV can clearly play 60 fps films, but not in XBMC.

maxsql · 2011-11-16, 22:21

What exactly do you mean by playing it in the standard GUI?
Via iTunes home sharing??

I also had issues with 60fps videos - also thought its a hardware limitation - which seemed plausible to me

hafr · 2011-11-16, 22:32

maxsql Wrote:What exactly do you mean by playing it in the standard GUI?
Via iTunes home sharing??

I also had issues with 60fps videos - also thought its a hardware limitation - which seemed plausible to me

Yes, via iTunes home sharing, as I said earlier Smile

The same file that plays in half speed in XBMC plays in normal speed when played on the ATV2 "as Apple intended".

maxsql · 2011-11-16, 22:37

I think that iTunes sends out a ATV compatible stream so It plays back smoothly.
XBMC decodes the "raw" video. There must be some kind of "conversion" when using home sharing

hafr · 2011-11-16, 23:18

In other words, there is nothing at all that points to a hardware limitation. The more I read about this, the more it seems like it's XBMC choosing to play it in 24 or 30 fps.

g-off · 2011-11-17, 00:38

It is clearly a conspiracy - or transcoding

hafr · 2011-11-17, 01:30

g-off Wrote:It is clearly a conspiracy - or transcoding

So... If I play a video on my ATV2 through iTunes, it's actually my computer playing the video and the ATV2 is just relaying the pictures, but if I play it in XBMC it's the ATV2 playing it?

g-off · 2011-11-17, 02:13

I don't actually know if itunes will transcode content through home sharing as I don't run itunes except for firmware. I was just being flippant. Although there is a good chance it does Smile

Post a mediainfo and a xbmc.log for the file in question otherwise you are just discussing how many angels can dance on the head of a pin.

hafr · 2011-11-17, 02:24

g-off Wrote:I don't actually know if itunes will transcode content through home sharing as I don't run itunes except for firmware. I was just being flippant. Although there is a good chance it does

Post a mediainfo and a xbmc.log for the file in question otherwise you are just discussing how many angels can dance on the head of a pin.

It's not a new issue, and everyone has the same problem with all of the files. This is what makes me think the problem of the slow video playback lies in XBMC and not in hardware limitations:

DEBUG: ReadEditDecisionLists - Assuming NTSC or 60i interlaced content. Adjusted frames per second from 59.940 (~59.940 fps) to 29.970

It's possible that the ATV2 can't process the file on it's own, but it's obviously not the reason why XBMC is playing it back in half speed...

g-off · 2011-11-17, 06:28

If you provide information about the problem it is more likely to be fixed. Make it easier for the devs by doing so.

hafr · 2011-11-17, 10:36

g-off Wrote:If you provide information about the problem it is more likely to be fixed. Make it easier for the devs by doing so.

Well, as I said this is not a new issue, and it has been reported in this very forum not too long ago, with file info, logs and everything. I think more of the devs than that they should need the same information over and over Wink

I've been in a situation where I handled problem reports, and there was nothing as annoying as getting the same problem reported over and over and over and over...