Tutorial: How to Restore A/V Sync to Variable Frame Rate Video for Editing in Premiere Pro

Have you ever shot video with your iPhone or with your iPad, 或者和Camtasia一起制作视频, and found that it looks and sounds great when you play it in VLC Player or in QuickTime, then you bring it into Adobe Premiere Pro and all of a sudden it totally loses audio/video sync? In this tutorial, we’ll tell you why that happens and more importantly, we’ll show you how to fix it.

The reason this happens is a problem with Premiere Pro--specifically with handling variable frame-rate video. 在我做过的项目中, I've seen this issue crop up in footage from an iPhone, footage that I've captured from Camtasia, footage that I've captured in Wirecast, and pretty much any program that captures in variable frame-rate mode. This problem has also been known to occur with Skype interviews captured with Call Recorder and imported for editing in Premiere Pro.

进入手闸

现在, the easy fix for that is a program called 手煞车. 手煞车 is a free cross-platform (Mac and Windows), downloadable tool. Basically, it’s a very elegant front end for the X.264编解码器. 图1(下面) 显示界面. You bring in your source file by clicking the Source button (shown with its tooltip in 图1).

图1. 手刹UI. Click the image to see it at full size.

选择手刹设置

In the example used in the video that accompanies this article, the file that I've been working with is iPhone.mov, and the file that we're going to create is CFR1 (for “constant frame rate”). After you import the file, there are just a couple of settings that you need to worry about.

Number one, you’re going to use an embedded preset called High Profile (on the right in 图1). Choose that to make sure you have a good starting point. 我们将使用射频编码. What RF encoding does is encode at a constant quality and if you drop the RF setting (下面的图2) all the way down to zero, you're going to get pretty much lossless quality. Even though you're encoding with X.264或H.264编解码器, you're not going to see any quality degradation.

图2. 将RF设置为0以获得无损质量.

The key configuration option you need to make is Framerate. You want to check the Framerate of your source--with the iPhone it’s 30--and then you want to make sure that you choose Constant Framerate (下面的图3).

图3. Make sure your framerate matches the framerate of the source video and—most important of all—choose constant framerate to lock that framerate in and make your video synced and editable in Premiere Pro.

That's the one thing that you absolutely have to do to make this work. 然后你可以检查音频, and then if you'd like you can boost the audio data rate up to around 320 or so to make sure that you get very little compression on the audio. Then you come back the video and press Start (up top, just to the right of Source in 图1). 当你按下开始键, 如果你有一个相当快的系统, 手煞车 should take one or two minutes for each minute of video.

现在, if you go back to Adobe Premiere Pro and import the 手煞车 video, you should find that the audio sync is perfect.

底线是, any time you bring video into Adobe Premiere Pro from any of these sources that do variable frame rate encoding and experience loss of sync, try the adjustment that we just made in 手煞车. 99%的情况下, just changing from variable frame-rate to constant frame-rate should give you perfectly restored A/V sync.