Problem synchronizing audio and video

[weareone]

Greetings. I recently downlaoded Total Video Converter 3.11, which is a helpful total for basic video conversion. The problem I'm having is that I do not see a way to synchronize the video with the audio when I use its multiplexing feature--that is, merge a MOV video file with an MP3 audio file. Basically, my video starts a tad earlier than my audio file, which causes the movements seen in the video to "happen faster" than the corresponding sound. The lack of synchrony results in large part from the fact that it's hard for me to start my digicam and my home recording software right at the same time. I'll work on that problem in due time. But, for the time being, I was hoping to find a software program that can fix this sort of problem. I think if I could add some dead space in the clip that I exported to an MP3, that would take care of the problem. But what if the audio has started before the video? Is there a program that could put such "dead space" in front of a MOV file? Basically, I just need a way to assure that the video recording and the audio recording are synchronized? Do you have any suggestions as to how I might be able to do this? Thank you for your time and for your input.

[redwudz]

Some video editors can do that, like VirtualDub. You can add a negative or positive 'skew' or offset to the audio track. One of the difficult problems with audio offsets is telling how much is needed. Some players like MPC have a offset control where you can correct the sync, then use that number for your 'skew' correction. And as you mentioned, you can add some silence to the beginning of a audio file or even cut some of the audio out to make a correction.

You also need to determine if the audio sync error stays the same for the length of the video. If not, then that's a different sync problem. That's usually caused by the video and audio being different lengths. You would have to change the length of one or the other.

It's also important to determine why you have this problem. If it's not one of your files, it could be bad cuts and joins, framerate conversions, VBR audio, a corrupted file and a few other causes. If it is your file, don't do whatever you did again. It a lot harder to fix than to prevent.

There's really no simple way to tell if a video and audio file are in sync, you just have to play it.

[weareone]

Let me get this straight: Even if I turn the digicam and the home recording software on right at the same time, the sync will be off if one file is longer than the other? If true, this would mean that not only do I have to turn the camera and the program on at the exact same time, I must turn them off at the exact same time. Practically, I don't think this is possible. Thus, it almost seems that you would have to be a video editing pro to get a perfect sync, like you see in concert videos. Based on the quality of the sound I hear when I watch concert videos, I assume the task of recording the music is independent of the task of shooting the video. However, you can still hear the fans as well. Thus, I infer that they just merge the audio that they've recorded into the computer or the high-end recording device into the track with the video--and audio-- that they capture with the camera. As I on to something here?

[poisondeathray]

Can you clarify what you are doing? Are you recording a video and then an audio track separately? If I'm understanding correctly, you can just shift the audio earlier or later to match the video. (e.g. if audio 1 sec too early, just do a +1000ms delay, etc...)

What is your final goal in terms of format? Leave as .MOV? Make a DVD? Make an .AVI? This determines what kinds of software you might be able to use. .MOV is not the most user friendly format. Is your .MOV the same as apple quicktime? Run mediainfo on a sample clip and post the results here.

[redwudz]

Yes, I'm a bit confused also. If you are capturing a video, the audio and video should start at the same time and not have sync problems most times. Are you talking about a web cam?

No matter, it should still stay in sync. With a concert video, it's a bit more complex. They usually capture the audio from the mixer board and even if they use several recorders, they can sync them up afterwards. If you remember the old clapperboards on early movies, that's one way to sync the video with the audio. They use a similar electronic method.

With most video captures, generally the audio is recorded with the video and then you wouldn't have sync problems. I'm not sure what you are doing.

But if you have sync problems, they can be fixed most times.

Other than that, if your video and audio are different lengths, you will definitely have sync problems.

[weareone]

I am trying to upload a video to Youtube. As I didn't want to disturb my neighbors with blaring guitar music, I decided not to record the music directly into the computer (I had headphones on). So, the digicam is recording what I am doing, including the ambient audio-- in other words, the weak sound of my non-distorted electric guitar. I tried to turn on the camera and the record button on the home recording software at the same time, in a crude attempt to sync the video and what I was recording with the home studio software. Likewise, when I was finished with the lesson, I tried to turn off the camera and my take on the recording software. Now, I have two files on my machine.

(1) MOV file made with my camera, containing video and ambient (i.e. room) audio
(2) MP3 file of what I recorded into the computer

So I used Total Video Converter to extract the stereo audio from my MOV file, so that just a MOV file without audio remained. then, I used the multiplexing feature to merge the soundless MOV file with the MP3 recording. This didn't come out bad in terms of sound and resolution. In fact, I am quite satisfied with it.

What I am not satisfied with is that the video is not totally in sync with the audio. There is a delay between my movements and the sounds that correspond to them. I suppose I should have added empty space (.25 secs or so) before the home recording track that I exported to an MP3 file. However, I neglected to do that. Can you think of anything else I might have done to fix the sync problem?

Now, I also would like to now what I should do in the event that the audio starts before the video. In this case, it seems that the easiest thing to do would be to add some empty space before the video track. However, as I am recording with a digicam and transferring it to my machine as a MOV file, there really is no track to speak of. That's why I was hoping to find a program, preferrably free, that would turn my MOV file into something that can be edited. Once edited, I suppose I could save it as a MOV file and then use Total Video Converters multiplexing feature--or some other software app you recommend--to merge it with the mp3 sound file.

I hope I did a better job of clarifying myself this time. If there is till something that you don't understand, please let me know.

[poisondeathray]

One approach would be using avidemux. If your audio & video are roughly the same length, it should work, otherwise you may need to cut some video off (with avidemux) or an audio encoder to cut some audio off.

You can also use YAMB to demux if you want, but you should be able to open the .MOV up in avidemux, and specify the audio from another track. (audio=>main track=>audio source=> (drop down menu) => external mp3 => point to location "external file"

On the video sidebar, set "copy"

Audio sidebar, set "mp3". You can also do the audio shift. In this example I have set +250ms (see attached). Adjust as necessary

Format, set "mp4" - (in the photo it says "AVI", but I bet your .MOV is h.264, and h.264 doesn't always play nice with AVI) It shouldn't matter since YouTube re-encodes everything anyways

Press save, with extension (e.g. "myfile.mp4")

[weareone]

Thanks for that response I'll see if I can try that tomorrow. I'll keep you posted.

I suppose I'd also like to know if you can shift a MOV file as you did the MP3.

[weareone]

Poisondeathray,

What you told me to do worked like a charm! I simply shifted the mp3 200ms and thereby obtained a good sync. Thanks a lot for uploading thoses screenshots. That made my task much easier.

I have a couple other questions, if you don't mind.

(1) Could you use Avidemux to shift a video file (MOV in this case) in the same way that you can use it to shift an audio file.

(2) How can I edited off (that is, delete) the last ten or so seconds of my MOV file with Avidemux? If I do this, would I have to do the same to my mp3 file before multiplexing them? If so, can Avidemux be used to do such a thing--that is, delete the last 10 s of a music file. I know that I could do this to the home recording track from which the mp3 was originally exported. However, I deleted the track by mistake.

[weareone]

Poisondeathray,

What you told me to do worked like a charm! I simply shifted the mp3 200ms and thereby obtained a good sync. Thanks a lot for uploading thoses screenshots. That made my task much easier.

I have a couple other questions, if you don't mind.

(1) Could you use Avidemux to shift a video file (MOV in this case) in the same way that you can use it to shift an audio file.

(2) How can I edited off (that is, delete) the last ten or so seconds of my MOV file with Avidemux? If I do this, would I have to do the same to my mp3 file before multiplexing them? If so, can Avidemux be used to do such a thing--that is, delete the last 10 s of a music file. I know that I could do this to the home recording track from which the mp3 was originally exported. However, I deleted the track by mistake.

Okay, I see how do you use Avidemux to delete part of a video. I cut off the last end so that it went from 7:31.7 s to 7:24. Now, I presume I have to edit the mp3 that I intend to merge with this soundless video file so that it is 7:24 s (or 7:24 minus the 200 ms I intend to shift it). Can I use Avidemux to do this? If not, do you know of any other free programs that would?

[poisondeathray]

Avidemux can't do audio cutting by itself. Audacity is free and does simple editing; should work for you

Just to let you know .MOV is just a container (like AVI, or MKV) and usually has h.264 video and AAC audio streams. So no you can't "shift a .MOV" like you do with audio

Sometimes you can use audio & video of different lengths - amazingly it's worked for me before. If it doesn't work just trim either the audio or video (whichever is longer)

Good luck

[weareone]

Avidemux can't do audio cutting by itself. Audacity is free and does simple editing; should work for you

Just to let you know .MOV is just a container (like AVI, or MKV) and usually has h.264 video and AAC audio streams. So no you can't "shift a .MOV" like you do with audio

Sometimes you can use audio & video of different lengths - amazingly it's worked for me before. If it doesn't work just trim either the audio or video (whichever is longer)

Good luck

Thanks for your help. After downloading TVC, Avidemux, and Audacity, and following your suggestions, I was able to get a couple of pretty good syncs!

There is something that still doesn't make sense to me, however. It's that when I enter a positive value in the shift field on the Audio pane in Avidemux, the video seems to move forward relative to the audio. That is, in the case in which the audio is playing ahead of the soundless video on the multiplexed video, the solution is to enter a positive value in the shift field. To me, this seems counterintuitive. Entering a negative value in the shift field would seem to be the solution in such a case.