audio, out of sync

[topshooter]

so I encoded a video in 1024x576 with 128kbps ac3 2 channel
the video plays fine with no artifacts
the problem is the audio is out of sync, but when played on VLC its perfectly in sync
is this a problem with my encode or with SMS?
heres a 1 minute clip of the video

http://www.megaupload.com/?d=L82D08PD

[psi88]

you can change the a/v offset by pressing O on the controller and then adjusting it by .25 of a sec at a time with L2 and R2

[topshooter]

i'll give that a try

[topshooter]

seems like using this causes more cpu usage, because it noticeably starts dropping frames and creates a skipping effect... im hoping EEUG will know why its out of sync to begin with

[qwerty159]

I'm also having an issue with audio sync. My entire video library is out of sync to varying degrees, sometimes by -.125, sometimes as high as -.375 seconds. They're mostly xvid DVD rips. Slipping the audio by hitting the circle button + L2/R2 helps, but it seems to gradually creep back out of sync and it's tough to get it dead on in 1/4 second increments.

I don't see that many people posting this issue, so do I assume that usually SMS works with perfectly sync'ed audio for most? I wonder if I need to turn off the dolby support or investigate sync parameter three in the menu. I'm using a Western Digital usb hard drive.

[dlanor]

Originally Posted by qwerty159

I'm also having an issue with audio sync. My entire video library is out of sync to varying degrees, sometimes by -.125, sometimes as high as -.375 seconds. They're mostly xvid DVD rips. Slipping the audio by hitting the circle button + L2/R2 helps, but it seems to gradually creep back out of sync and it's tough to get it dead on in 1/4 second increments.

This problem is mainly due to the widespread use of VBR (Variable BitRate) for MP3 encoding. This is an excellent way to keep audio MP3 files small for the given average bitrate, and then the (inevitable) loss of precise timing does not matter. It does matter a lot when combining that audio track with a video stream though, as that needs perfect sync (which is impossible with VBR) for perfect viewing pleasure.

Modern PC players can afford to waste a lot of CPU power on forcibly adapting the audio replay to adhere strictly to the average rate specified, thus minimizing the average sync 'slippage', but local variations of sync differencies will always occur with VBR MP3 sound, though it may be reduced to unnoticeable levels.

A PS2 player (and many cheap DVD players) can not waste sufficient CPU power to do such 'average rate adaption' well, and therefore suffer more extreme sync problems as gradual slippage accumulates for the entire length of a movie.

I don't see that many people posting this issue, so do I assume that usually SMS works with perfectly sync'ed audio for most?

No, I don't think so. But I'm sure many do what I do, which is to convert all videos/movies having VBR sound to use CBR sound instead (still MP3), which has no such problems.

I wonder if I need to turn off the dolby support or investigate sync parameter three in the menu. I'm using a Western Digital usb hard drive.

None of those factors should be responsible for this problem.

The only way to eliminate it completely is to convert the audio track to CBR (Constant BitRate) by re-encoding it. For this I use VirtualDub and set it up to use "Direct stream copy" for video and "Full processing mode" for audio, and choose an MP3 codec for the audio "Compression..." setting, which opens a configuration dialog where I set that codec to use an appropriate CBR bitrate.

For non-music movie/TV material any rate from 96kbps and up should do fine. I use 96kbps myself for most TV shows, but not all codecs support that rate, in which case 128kbps is the standard choice.

You also need to ensure that you choose a bitrate encoding with suitable sample rate, so if the original encoding (as checked by GSpot) used 48000Hz, then you need to choose an encoding using the same (most releases use either 48000Hz or 44100Hz).

Just make sure the chosen encoding isn't shown as being VBR or ABR (different name for the same thing, calling it Adaptive instead of Variable).

It may sound like a lot of work doing this for every downloaded video, like I do, but it really isn't that hard. VirtualDub has a 'Job control' system that allows you to process entire folders of videos using the same settings, so there's no need to set them up per video. You don't even have to set them up per session, as the settings can be saved for future reuse.

For a normal conversion session I simply do the following:

1: Launch VirtualDub
2: Use the command "File" / "Load processing settings..." to get my conversion settings
3: Use the command "File" / "Job control..." to open the job control dialog box
4: In the box, use its command "Edit" / "Clear list"
5: Still in the box, use its command "Edit" / "Process directory..." to select two directories
(The first one holding your original videos, the second one for new encoded copies.)
6: Still in the box, click its button entitled "Start"

And that's all there is to it. VirtualDub will then start the conversion file by file, and since this just affects the audio tracks, it shouldn't take very long. Just a few minutes for a normal TV show even on a very average (or even sub-standard) computer (like mine ).

Best regards: dlanor

[nickblame]

that is a bit sad though :/ I have the same issue with most of the media I have lying arround and there is no chance I re-encode all these things just to watch them on ps2. playing media from usb is easy. that is the whole idea. if i need to re-encode it is not easy anymore.. it is easier to plug my laptop in the tv using tv-out rather than re-encode.

is there any chance that this is fixed in future releases? at first i thought the problem was the usb1.1 bandwidth limit that caused this audio lag in some files.

don't get me wrong I'm greatful for sms!

[nickblame]

wait, i get audio out of sync on a mpeg1 video file with cbr audio

Sys Bitrate: 1411 kb/s (224 of which is the audio)

[nickblame]

i'm confused. I also tested an xvid 1226kbps with 121 kb/s mp3 audio vbr and it was all synced. is it really a cbr/vbr audio this issue?

[dlanor]

Originally Posted by nickblame

i'm confused. I also tested an xvid 1226kbps with 121 kb/s mp3 audio vbr and it was all synced. is it really a cbr/vbr audio this issue?

I never said that VBR was the only cause of such problems, nor that it always is noticeable even with VBR. But it is most commonly caused by VBR, and then the problems can usually be eliminated by the kind of conversion I suggested.

This VBR problem I wrote about is not SMS-specific, but affects other players too, including my cheap DVD/AVI player which was the reason I started converting videos that way.

As for the other types of problems that may cause SMS to lose sync, I think it better that EEUG himself explains those issues, as he knows best the limitations of the program he wrote.

Best regards: dlanor

[qwerty159]

Thanks for the replies, I especially appreciate all the info from dlanor. So it turns out that most of my files actually have ac3 audio... Would they still be affected by the same timing issues that vbr mp3 can pose?

I did further testing and the audio seems to be off by about the same amount throughout the movie, perhaps it's rather that the audio offset controls don't allow a fine enough degree of adjustment to sync it dead on.

Maybe SMS could add the ability to adjust audio +/- offset by .10 of a second instead of .25 in a future update?

[dlanor]

Originally Posted by qwerty159

Thanks for the replies, I especially appreciate all the info from dlanor. So it turns out that most of my files actually have ac3 audio... Would they still be affected by the same timing issues that vbr mp3 can pose?

No. AC3 is CBR only, as far as I know anyway.

I did further testing and the audio seems to be off by about the same amount throughout the movie, perhaps it's rather that the audio offset controls don't allow a fine enough degree of adjustment to sync it dead on.

If the sync offset is constant, then a minor adjustment at the start of the movie (using the controls of SMS) should suffice.

Maybe SMS could add the ability to adjust audio +/- offset by .10 of a second instead of .25 in a future update?

Perhaps, but that's up to EEUG (as for all SMS changes).

Anyway, even with .25 sec resolution, you can always pinpoint any constant offset to within one 8th of a second (.125 sec), which should be fairly acceptable as-is.

Best regards: dlanor

[qwerty159]

After further testing, it seems just about every movie starts off at -.125 off and slips to around -.300 by the end of a 90 minute film. I usually end up sliding it back by .25 every 10/15 minutes to keep it roughly sync'ed. This is regardless of audio codec, so maybe it could be the usb connection? And yeah, I guess .25 increments work well enough.

[solidus27]

dlanor, can you give us a link to a VirtualDub tutorial? I con't even fint the convert button! And I have no ideea to w/ video format I'm converting!

EDIT: NVM, I found this tutorial, but if you have a better one, pls post dlanor!

[dlanor]

Originally Posted by solidus27

dlanor, can you give us a link to a VirtualDub tutorial?

Sorry, but I've never used any, so I don't really know what's available.

I con't even fint the convert button!

There is none. For normal single-file conversions you start by opening your source file and then select the various encoding options for video and audio, finally you go to the 'File' menu and use the command 'Save as AVI...'

And I have no ideea to w/ video format I'm converting!

Obviously not, since you don't know the program well yet.

But it's not all that hard, really. The only 'container' supported is AVI (so no MKV complications etc), and the video encoding is chosen simply by using the menu command 'Video'/'Compression...' which opens a codec selector, where you also have the option of further configuring the chosen codec. Normally I just choose the XviD codec and configure it to use a suitable bitrate. Around 1000 kbps is fine for normal TV shows/movies, and I never bother with more than a single pass (multi-pass is horribly slow, though it does produce more efficient packing).

But most of my own conversions are only for changing the sound track, so I use the settings 'Video'/'Direct stream copy' (to avoid changing the video) and 'Audio'/'Full processing mode' (to allow tweaks to the audio track), after which I choose the 'Audio'/'Compression...' command to choose the MP3 codec and configure its settings. At this point it may also be a good idea to save the conversion settings for future use in job control, by using the command 'File'/'Save processing settings...'. And then all that remains is to use the 'File'/'Save as AVI...' command to choose where to save the result of the current conversion. And that starts the conversion process.

Once you have suitable processing settings saved to a VCF file, and have a batch of video files that need similar conversion, then it becomes much more convenient to use the job control feature, as I described in an earlier post.

EDIT: NVM, I found this tutorial,

Unfortunately that is a tutorial on video capture, not video conversion, but perhaps it may still help you familiarize yourself with the program. But I really think you should try to find another.

but if you have a better one, pls post dlanor!

I'm afraid not. But I'm sure google can find some.

Just entering: "VirtualDub tutorial" (without the quotes) into the google search box brought up tons of hits when I tried it, though I can't say which of them are any good.
(The total number of hits was rounded to 241,000, so you'll have to pardon me for not checking them all out. )

Btw: VirtualDub itself does not contain any codecs, so it can only use whatever codecs you have installed by other means. (You probably already have all you need though.)

Best regards: dlanor

[solidus27]

Thanks alot dlanor. As always, very helpfull!

[qwerty159]

After watching a bunch of movies over the weekend, I've come to terms with this and have found that simply pausing the movie for a second every 20 minutes or so will keep the audio roughly in sync.

So if I start out at -.125, I can usually just stay there if I pause a few times. The audio issue is not as bad as I initially thought and seems to have no relation to the audio encoding in the movie files. Try this approach before re-encoding your collection if you're having problems. It's not perfect, but it's close enough that an average person probably wouldn't notice unless they were looking for it.