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Audio drifts out of sync over time

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Matthew Belinkie
Audio drifts out of sync over time
on Nov 10, 2014 at 3:33:30 pm

Guys -

I am banging my head against the wall trying to figure out how to convert this bunch of videos to a usable format. Here are the specs according to Quicktime:
AVC Coding, 1,920 x 1,080
AAC, 44100 Hz, Stereo (L R)
30 fps

I can open them with Quicktime and the audio seems perfectly in sync. However, when I use them as part of a Premiere sequence that must be 29.97, 48000 Hz, the audio drifts out of sync over the course of like 15 minutes.

I've tried to convert the raw files to all sorts of formats, from ProRes to MPEG-2. I've tried Compressor and Adobe Media Encoder. No matter what I do, the resulting file goes out of sync gradually. This is true EVEN IF I make the settings 30fps and 44100 Hz, identical to the original. The only way I can make the video stay in sync is playing it in Quicktime.

If I had to guess, I would guess the problem is that the source files are variable framerate, and none of the encoders are dealing with that. That's why the audio drifts over time. But even if that's right I have no idea how to deal with it.

Any suggestions guys? I'm close to giving up and manually adjusting the sync every five minutes. That would suck, but right now I'm dead in the water.

- Matt

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Michael Krupnick
Re: Audio drifts out of sync over time
on Nov 11, 2014 at 10:25:00 am

This is a sequence at 48K and source at 44K audio rate…an elementary error in matching the project into compliance with the raw files. There are a number of ways to adjust for that and set up the project properly, all easy. When the sample rates match, the sync will stay solid.

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Matthew Belinkie
Re: Audio drifts out of sync over time
on Nov 11, 2014 at 11:24:04 am

If ONLY it were that simple. Trust me, I've fallen for that before, but this is something way more stubborn. Even when I put the files in a 44100 sequence, the sync is way off. Even when I play the files in the VIEWER, no sequence involved, the sync is way off. Premiere just hates these files. But when I open the originals in Quicktime, they play totally fine.

I did discover a time-consuming workaround. I bring the mp4 files into Final Cut Pro 7, drop them on a timeline, let the sequence conform to whatever format it thinks the mpg files are, and then export that. Then I have a Quicktime .mov file that is mysteriously 50% larger than the original mp4.

That STILL doesn't sync in Premiere. However, I can bring that .mov file into compressor and convert it to an MPEG-2. Bingo, that works fine. It takes forever but at least it works.

The best I can figure (and this is just a guess) there's either a variable frame rate thing going on, or maybe the occassional frames that are corrupted. Quicktime handles this stuff different than Premiere to keep video and audio in sync. I just needed to find a way to convert the file to preserve the sync that Premiere would work with.

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James Poll
Re: Audio drifts out of sync over time
on Nov 11, 2014 at 1:39:19 pm

I get this problem all the time, usually with files coming from an iPhone or iPad which uses VBR compression.

The only way I've been able to work around it, is to convert the source files to a new QuickTime file using MPEG Streamclip ( Streamclip seems to be able to do the conversion without the audio drift.

Hope this helps. Good luck!

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Ht Davis
Re: Audio drifts out of sync over time
on Mar 7, 2015 at 7:57:17 pm

Streamclip is good. And the reason the file is bigger is because you're using different compression method, resulting in more data being stored in the file... Just an FYI.

My workaround is to use AE, drop the video into a COMP with strict settings and render out to a MOV file or another intermediate file type (prores, intra, etc). Just make sure you match your sequence settings with the comp from AE.

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Ht Davis
Re: Audio drifts out of sync over time
on Mar 8, 2015 at 11:52:25 pm

It sounds like the camera has an image stabilization algorithm that alters the frame rate.

Process the video out to an intermediate first (doesn't matter which one).
When you are setting that up, just remember the following:
You need to specify the exact frame rate--no Automatic from source, as this will allow frame rate changes, resulting in a VFR instead of CFR (CFR is constant frame rate).
You need to set the size, and the field order, as some algorithms actually change these as well--I shoot progressive, so I set progressive, then output to interlaced only when I cannot output to PSF (a fake interlace).
If you do this correctly, your AV will be synced in premiere. But there's more adjustment you can make:

decide how much headroom you want to keep for your audio and how "real" you want the variation to be. Headroom will be your KHZ (sample rate) which will give you some background noise and fill to play with if you go with 96khz or higher, will give you warm and true audio in 48khz, and will squeeze into 44.1khz to limit file size. Your bit width will determine how "real" the differences can get (how deep the decimals go and how big or small the numbers get in general. 16bit is CD quality, but usually isn't for any kind of professional video\audio combination, unless you can engineer the sound in an advanced manner.

I used iMovie, imported the clips, sent them to compressor, and transcoded out to prores, which decompressed and created a proxy for me to use (2 transcodes, but that way I can load the first, place it, and then relink to the proxy for work.

Differences in editors:
Premiere doesn't go down to the subframe level. Most editors today do (especially final cut), but do so by creating an intermediate frame between them. Premiere doesn't create intermediate frames unless you apply some sort of motion effect or cleaning, and retime the frames.
Premiere is a professional oriented program. Most pros work in one standard frame rate that doesn't change. Some consumer devices, however, vary frame rates with motion, in order to make the output look better or keep the camera shake to a minimum. Most editors enable this to work fine, and will create the intermediate frames if you tell them to, or when you output your final product, but Premiere only edits a standard video stream, it doesn't "Create" the video frames. Rather, it orders the effects and frames you put together in a timeline that builds to a single frame rate video output. Premiere is more a LINEAR EDITOR than a NONLINEAR EDITOR. After-effects should be able to do the same as compressor, and do a better job than MEDIA ENCODER, as you can set more strict output profiling in your COMP, so that it forces the frame rate and the size.
I chose compressor because I could run it on more than one machine and output a video directly (farming), and it doesn't just output images from the farm.

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Ht Davis
Re: Audio drifts out of sync over time
on Mar 12, 2015 at 7:56:57 pm

I've found the above issue to be heavily related to cameras using image stabilization in camera. It adjusts frame rates to "steady" the image.

I have used adobe to fix it... ...AME will fix this problem, but will slow the motion down a bit, almost slowmo in areas where there is heavier drop, but I've found that even the speech being watched matches up alright. You just have to select "USE FRAME BLENDING". You can do the same in AE, but AME is faster. I outputted Prores files with and without. Without, I had the same issue, with the blending, it was fixed. I then dropped the output frame rate... ...nearly destroyed the motion quality. I did the same with AE, but it took 12 times as long to process; I used twixtor afterward and had it render without the blend... ...Twixtor will create the frames in-Comp, but to render them out will take even longer, as the quality is much higher. I stopped this render when it was taking too long. I checked the quality of my other tests, and they were acceptable for the purpose of my video, so I rendered out fully using AME to output a prores LT422 profile and frame blending to force a constant frame rate.

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steve knattress
Re: Audio drifts out of sync over time
on Apr 5, 2015 at 3:50:39 pm

The is no image stabilisation with a "broadcast" VIO POV_hd headcam, but it does record VBR (see below)

In all my files the audio drifts way out of sync when brought into a "same as" sequence (dragged and dropped into new sequence)

Every other audio app I try the sync is fine.
Even Avid media composer remains in sync under AMA with these files.

* * * MediaInspector for Mac - Version 2.6, build 953
* * * ©2012 by Diego Massanti
* * * MediaInfo Lib by Jerome Martinez
* * * Raw File Report for 2015 Apr 01

Complete name : /Volumes/2015Drobo/Media/POV_HD_2015/2015_04_01/DCIM/2015 Apr 01
Format : MPEG-4
Format profile : QuickTime
Codec ID : qt
File size : 3.91 GiB
Duration : 34mn 54s
Overall bit rate mode : Variable
Overall bit rate : 16.1 Mbps
Encoded date : UTC 2015-04-01 08:15:20
Tagged date : UTC 2015-04-01 08:15:20

ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4.1
Format settings, CABAC : Yes
Format settings, ReFrames : 1 frame
Format settings, GOP : M=1, N=30
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 34mn 54s
Bit rate : 16.0 Mbps
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Variable
Frame rate : 25.000 fps
Minimum frame rate : 12.500 fps
Maximum frame rate : 25.773 fps
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.309
Stream size : 3.90 GiB (100%)
Language : English
Encoded date : UTC 2015-04-01 08:15:21
Tagged date : UTC 2015-04-01 08:15:21

ID : 2
Format : AAC
Format/Info : Advanced Audio Codec
Format profile : LC
Codec ID : 40
Duration : 34mn 54s
Bit rate mode : Variable
Bit rate : 64.0 Kbps
Channel(s) : 1 channel
Channel positions : Front: C
Sampling rate : 16.0 KHz
Compression mode : Lossy
Stream size : 16.0 MiB (0%)
Language : English
Encoded date : UTC 2015-04-01 08:15:21
Tagged date : UTC 2015-04-01 08:15:21

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Ht Davis
Re: Audio drifts out of sync over time
on Apr 6, 2015 at 4:01:06 am

Frame RATE MODE: VARIABLE = in camera VFR, most likely a stabilizer.

Stabilizer is automatic. No setting for it.

VBR or Variable Bit RATE is a data standard. It has little relevance in sync. It corresponds to the compression method, not the actual photographic properties.

I can record a video on a film camera at any frame rate and as long as that rate remains constant, the sound that goes with it will sync up just fine. If I change the frame rate while shooting, and the sound is still recording at the same rate it was at the start, they will fall out of sync. I have 2 choices in analogue edits... ...try and apply my own soundtrack or stretch\squeeze the sound as needed (speed up slow down).

In digital, there are mechanisms that will drop a frame or two based on the motion of the camera or the scene. Check your specs again. It may be a built in stabilizer. It will drop frames or speed up and add frames per seccond in order to remove the camera shake. This can be based on an accelerometer (the better way usually) or an estimation from the edges of the frame (which could be moving due to actually being on some kind of vehicle. Most often, it drops frames. When storing digital video, the files can get really big, so the images for the frames are COMPRESSED. Most of the time this loses some quality, as the images are, themselves, jpeg (by design a compressed image format). There are frames that are stored fully, and then other frames are compared, and the changes are stored, the rest dropped. The calculation for tracking those changes defines how much data each second of video will take up (the Data or BIT rate). A constant measure of data will force some frames to have better quality than others. A variable bit rate keeps the quality, but drops varying amounts of information. If your camera records at a VARIABLE BIT RATE, it is a STANDARD PROSUMER GRADE VIDEO CAMERA! Truly proffesional level cameras also have a VBR, but they don't compress the footage... gets huge enough to require hard drives of hundreds of gb.

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steve knattress
Re: Audio drifts out of sync over time
on Apr 6, 2015 at 8:47:36 am

So if this were true all editing applications would exhibit this sync drift. Why is it that premiere pro is the only one that does? What is pp doing when it spends time "confirming" audio? Looks like I'll be back to a "professional" application avid a a us fine ;)

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