Audio timestretching on Movie Edit Pro MX

peter-n86 wrote on 5/9/2016, 7:54 AM

Hello everybody and thanks for your help in advance: this is rather complicated, I'm afraid. I am trying to correct a video which had a fault when it was recorded, namely that the audio and video do not match perfectly until the very end. I have to resort to timestretching as I do not want to change the pitch of the audio. I realise that I have to ungroup audio from video first and I can timestretch for the whole audio file in one swoop, but this is not the solution in this particular case as it needs modifying constantly throughout the video. If, after editing, it fits at the beginning, it's out of sync later on. Therefore, I obviously need to timestretch in small parts throughout the video so that everything matches up in the end. But how do I select parts of the audio to do so? As far as I can see, I can only select the whole audio file. I want to be able to stretch the audio every minute or so by varying degrees. How do I go about this?

Comments

johnebaker wrote on 5/9/2016, 10:09 AM

. . . . I am trying to correct a video which had a fault when it was recorded . . . .

I suspect that the issue is caused by a video with variable framerate which can give syncing issues with the audio in MEP.

What was the video recorded with and its format?

If the video was recorded in MPG format then try the following:

Right click the video and select Create frametable (new) then play the video to see if the audio is now synced.

If the video was any other format then you are going to have to cut the video clip up into small sections and stretch the audio appropriately for each section. This may cause issues with the audio ovelapping the different sections.

There are other options available however without knowing the video format, framerate and audio bitrate it is not possible to advise you.

You can determine the above settings using MediaInfo and post the results from the Tree view.

HTH

John EB

peter-n86 wrote on 5/9/2016, 12:39 PM

Thanks very much for helping, John! It was recorded on a digital camera in mov format, 1280x720, AAC audio. I tried creating a new timeframe anyway, but it didn't improve. The problem, which occurs suddenly at about 1 minute into the film, is very audible: there is a jump in the sound and suddenly the audio is ahead of the picture. Like a record player needle that has suddenly jumped a groove - it happens very suddenly. Then, towards the end of the film, at a certain point, the audio suddenly stretches (can't put it any other way: it's very audible) so that at the end of the film, it all matches up again. But for the majority of the film, it is out of sync. That's why I thought the only way to correct it would be in small sections (because it doesn't stay out of sync at the same rate all the way through). If I do have to cut it up into small sections, how do I do it? And how do I circumvent the problems of overlapping?

Thanks again, John.

Peter

peter-n86 wrote on 5/9/2016, 12:43 PM

Here's the info, John:

Format                                   : MPEG-4
Format profile                           : QuickTime
Codec ID                                 : qt   2007.09 (qt /niko)
File size                                : 677 MiB
Duration                                 : 11mn 14s
Overall bit rate                         : 8 424 Kbps
Encoded date                             : UTC 2013-12-29 19:30:32
Tagged date                              : UTC 2013-12-29 19:30:32
NCDT                                     : NCTG

Video
ID                                       : 1
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : Main@L3.1
Format settings, CABAC                   : Yes
Format settings, ReFrames                : 1 frame
Format settings, GOP                     : M=1, N=8
Codec ID                                 : avc1
Codec ID/Info                            : Advanced Video Coding
Duration                                 : 11mn 14s
Source duration                          : 11mn 14s
Bit rate                                 : 8 287 Kbps
Width                                    : 1 280 pixels
Height                                   : 720 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 29.970 (30000/1001) fps
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.300
Stream size                              : 666 MiB (98%)
Source stream size                       : 666 MiB (98%)
Language                                 : English
Encoded date                             : UTC 2013-12-29 19:30:32
Tagged date                              : UTC 2013-12-29 19:30:32
mdhd_Duration                            : 674069

Audio
ID                                       : 2
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 11mn 14s
Bit rate mode                            : Constant
Bit rate                                 : 128 Kbps
Channel(s)                               : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 KHz
Frame rate                               : 46.875 fps (1024 spf)
Compression mode                         : Lossy
Stream size                              : 10.3 MiB (2%)
Language                                 : English
Encoded date                             : UTC 2013-12-29 19:30:32
Tagged date                              : UTC 2013-12-29 19:30:32

johnebaker wrote on 5/9/2016, 1:31 PM

Thanks for the MediaInfo data.

It looks like a standard HD file except for the line . . . Frame rate: 46.875 fps (1024 spf) . . . in the Audio section, is not correct.

Audio files do not have a framerate - this leads me to suspect that the file is corrupt.

If the video was recorded to a memory card in camera then possible causes are:

the card is not of the correct speed rating for HD video eg you have a class 4 card when a class 10 is needed.
the card is developing a fault
a glitch in the camera firmware - though this would be rare - check to see if there is a firmaware update for the camera, or there is a known issue with it.

To cut the video up and adjust the audio ensure that the video and audio are on seperate tracks press Ctrl + H for the selected clip

Position the timeline cursor at the point where the cut is to be made and press the T key, then ungroup the video and audio using the ungroup button (broken link symbol) just above the timeline.

The individual sections can the have the audio timestretched.

The overlapping audio may mean you have to cross fade the audio if you cannot trim it at the correct point.

HTH

John EB

peter-n86 wrote on 5/9/2016, 3:49 PM

Ok, thanks very much, John! Yes, the audio problem is quite strange but in this case not insoluble, thank goodness. Your help was much appreciated.