Audio out of sync

I found a funny bug recently when playing a video through the media player. Audio seems to be out of sync, but only only for videos with 6-channel AC-3 audio. All of the files that I play that have 2-channel AC-3, or DTS play fine. Normally I have my ATV set to pass audio through my TV to my receiver, but even with the optical audio going straight to my receiver, the problem still existed with videos with 6-channel AC-3 audio.

Not a big deal since I can convert the few video files I DL with 6-channel AC-3, but something to look into.


Anyone else have any issues with this? I have noticed when streaming TV shows everything is good, but I have tried a few movies now and the audio is out of sync just a fraction of a second, but it bothers my too much making watching the movie impossible.


I assume the TV shows and Movie must be encoded differently so maybe it is the same issue we are talking about… Anyone have a solution or advice?

What type of videos files are you having trouble with? Which tool was used to create them?

A bug report may be helpful in tracking down what’s going on.

I didn’t actually create the file so I can’t speak to how it was made, but here are the specs for the video:



Unique ID                                : 252000525862082910633282255115083262351 (0xBD95892F29EAD5A18C002B766397298F)

Complete name                            : C:\Users\Public\Videos\TV Shows\Community\Season 3\Community - S03E17 - Basic Lupine Urology.mkv

Format                                   : Matroska

Format version                           : Version 2

File size                                : 486 MiB

Duration                                 : 20mn 56s

Overall bit rate                         : 3 242 Kbps

Encoded date                             : UTC 2012-04-27 01:45:06

Writing application                      : mkvmerge v3.0.0 (‘Hang up your Hang-Ups’) built on Apr 19 2010 11:58:49

Writing library                          : libebml v0.7.7 + libmatroska v0.8.1



ID                                       : 1

Format                                   : AVC

Format/Info                              : Advanced Video Codec

Format profile                           : High@L4.1

Format settings, CABAC                   : Yes

Format settings, ReFrames                : 5 frames

Codec ID                                 : V_MPEG4/ISO/AVC

Duration                                 : 20mn 56s

Bit rate                                 : 2 794 Kbps

Width                                    : 1 280 pixels

Height                                   : 720 pixels

Display aspect ratio                     : 16:9

Frame rate                               : 23.976 fps

Color space                              : YUV

Chroma subsampling                       : 4:2:0

Bit depth                                : 8 bits

Scan type                                : Progressive

Bits/(Pixel*Frame)                       : 0.126

Stream size                              : 418 MiB (86%)

Writing library                          : x264 core 124 r2197 69a0443

Encoding settings                        : cabac=1 / ref=5 / deblock=1:1:1 / analyse=0x3:0x113 / me=umh / subme=8 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-2 / threads=16 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=5 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=50 / rc=crf / mbtree=1 / crf=18.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00

Language                                 : English

Default                                  : Yes

Forced                                   : No

Matrix coefficients                      : BT.709-5, BT.1361, IEC 61966-2-4 709, SMPTE RP177



ID                                       : 2

Format                                   : AC-3

Format/Info                              : Audio Coding 3

Mode extension                           : CM (complete main)

Format settings, Endianness              : Big

Codec ID                                 : A_AC3

Duration                                 : 20mn 56s

Bit rate mode                            : Constant

Bit rate                                 : 384 Kbps

Channel(s)                               : 6 channels

Channel positions                        : Front: L C R, Side: L R, LFE

Sampling rate                            : 48.0 KHz

Bit depth                                : 16 bits

Compression mode                         : Lossy

Stream size                              : 57.5 MiB (12%)

Default                                  : Yes

Forced                                   : No


I’m no expert when it comes to audio/video encoding, but as far as I know this is the only 6 channel AC3 file I’ve ever tried to watch, and is also the only encoding configuration that I’ve seen this delay on.

I’ll submit a full bug report shortly.


Thanks for the specs. Is this file out of sync from start to finish, or does it begin somewhere in the middle?

We’re looking into a few issues where the audio stream can get out of sync due to some of the timestamps not matching up (usually due to commercials being removed from the middle of a tv show).

Thanks James. If you guys are already looking into a related issue, I’ll hold off on the bug report for now.

It’s out of sync right from the start, so not related to commercials being edited out. The audio and video sync perfectly when played on my computer too, so it definitely has something to do with the media player on the ATV.

I actually did try and down-convert the audio from 6-channel to 2-channel, but that didn’t seem to help…so really not sure what it is about the specs of this video that are causing the problem.

Keep up the good work guys.

Hmm, if it’s out of sync from the start it may be best to send in a report.

A sample file could also be very helpful if you’re able to manage.

Okay, I’ve put in a report (#32416 Audio out of sync), but the sample for the video was too large (25mb) to attach to the bug report ticket. Is there anywhere else you would want me to send it? I have a Dropbox account I can share a folder with you on temporarily if you wanted to grab it from there.

I have the same problem with ac3 6 channel sound going out of sync. It’s a recent development.

I have similar issues and only when playing movies through Media player, all files work perfect viewing through iTunes. The recent version 1.7 hasn’t made any difference, a big pain as I purchased this package purely for Media player.

Same problem here. After a couple of seconds the 6-channel ac-3 is out of sync. But not in all files with 6 channel sound. It is totaly  weird.

Send you guys a bug report via the atv settings.

Hopefully you will fix the fast. 

I finally got around to updating my ATV and still no luck. As the others mentioned, the audio still seems to be slightly out of sync on the 6 channel AC-3 files.

I have the same problem with tv shows (.mkv) where commercials have being removed.
However, the same file plays very well with Kodi.