export to mp4 audio out of sync

Question

export to mp4 audio out of sync

I have a .mov that I'm trying to export as mp4 for web streaming. Actually this is the 2nd I've done and the first went OK. But the 2nd one loses it's audio sync with the video. audio is slow and gets off by maybe 2minutes by the end of the 45 minutes. The .mov is fine but the sync problem is happening when I export to mp4
Here is what I've done:
I record a webinar w/screenrecord2 and first I tried quicktime pro export (Boy it took a long time!!) to mp4 w/default (H.264, 640x480) except slower frame rate and set for webstreaming. The audio sync was off.
I read something about hinting helping audio sync problems so I then tried export to a hinted .mov and then to mp4 and still not good audio sync.
Next I tried export the hinted .mov via Streamclip and it went much faster and better video quality than the export via quicktime pro but still the audio loses sync.
The .mov is about 2.5gig and 45 minutes long exported mp4's about 80meg
Any help is much appreciated!

Is there a way in quicktime pro that I can speed up the audio of the mp4 and get it back into sync??

imac 2.4 duo, Mac OS X (10.5.2), 2gig ram

Posted on May 26, 2008 8:21 PM

Reply

Answer 1

May 27, 2008 5:56 AM in response to Robert Schwenkler

Hi Rob, sounds like a bit of a pain.

Command J when the move is playing and have a look under the properties and see how long the movie is and how long the audio. Naturally you would expect them to be the same but they rarely are. I find on a average a 10 second difference but on oaccasions up to 40 and thats where the real time drift happens.

Are you exporting to a different audio sample rate?

You could try exporting the the audio as an AIFF using QT pro, look to see in a wave editor if there are any anomalies i.e. a section of silence that shouldn't be there compared to the movie and try and remove it. Save as an AIFF and reattach the new audio using QT Pro.

For the future QT synch is a great app but will only really help you to correct a file where the sync is the same throughout. Also hinted files only add streaming data for streaming servers, get this, even if you correct sync when the hinted file is made the streaming player will still revert back to the original out of synch version...strange?

Cheers

Reply

Answer 2

May 27, 2008 10:11 AM in response to The Dougfather

Thanks for the response... properties shows both sound and video at same length... actually off by a few hundredths 35:01.50 35:01.53 There are two things going on... if .mov is OK for the web I can just put my hinted .mov original at 2.6gig size and use that- that is the easiest.
Can pretty much anyone view the .mov format? Is mp4 more viewable? I'm thinking quicktime needed for .mov but mp4 can be viewed by quicktime plus windows and other viewers??? I'd like to just post the .mov and stop spending time on this....

When I export to mp4 it's down to 80meg but I lose the sync. I did fool around a bit w/quicktime pro on the exported mp4 version and extracted the audio then chopped the original video by the 2 minutes it was off and paste back in the audio scale to fit and that fixed the sync problem but now I have a .mov again (it is 80meg now) and I'm not sure if it's still hinted for streaming and I did a re-export to mp4 and lo and behold the audio sync went off again...

Reply

Answer 3

May 28, 2008 5:01 AM in response to Robert Schwenkler

Hi Robert, i just want to check you are actually going to be posting your material to a real streaming sever i.e quicktime streaming server, darwin server, helix server.

If not then you won't actually be streaming the file, i've been doing a lot of work on streaming servers recently and the first thing i found was that the term streaming is often misused. If you are only posting your file on to a web server for people to view then quicktime has something called quickstart which will allow you to watch the video as it downloads like youtube, this isn't streaming.

With regards to extensions i would be much more inclined to use .mov over .mp4, it will make life easier for your viewers because you can guarantee at some point real player will try and hijack the .mp4 extension for some of your viewers.

Cheers

PS: Can you post hwre the file originates from, it's possible the problem stems from further up the chain but only comes to light when the file is exported. I find editing in quicktime and then exporting can often be problematic.

Reply

Answer 4

May 28, 2008 9:28 AM in response to The Dougfather

Thanks again for response!
What I did was strip the audio track via quicktime pro, shortened the video and re-added the audio selection to scale. With a little work this got things back in sync w/a smaller file size. Original files are from Screen Record2 program which I'm using to record our webinar.
As far as server I'm not sure... I put it to bluehost and it seems to work fine.. about a minute delay before it starts playing... except sometimes the audio stops playing and I pause/restart and it's OK again. I don't think they are darwin/helix.
I have the option to go to my .mac server but it is a pain in the butt to work with and I seem to get better response with video from bluehost.

Reply