Blackmagic Forum

Hello,

I have some MP4 clips on my computer that I needed to trim down and export. I've done this many times, but all of a sudden today all of my video segments have their audio clipping constantly in Resolve.

For example, I play my 30s video in VLC and the audio is perfect. After dragging it in to Resolve and watching it in there, the audio is constantly clipping.

Not sure how to solve this. I can record my monitor and show me playing both separately if needed but thought I'd check and see if someone knows of this issue first before doing that.

Thank you for your time,
Castle

I have the exact same problem. Been using Resolve for a few months (and loving it) but just imported a .mov clip and it's seriously clipping. But plays perfectly in VLC. I'm using the latest Resolve (16.2.1.017) and here are the (sorta weird - thanks Apple) parameters of the clip:


Any ideas?

Would either of you care to share a sample file that exhibits the issue?

Check your sliders in Fairlight ... I had an instance where they were very different from the past 18 months
... an easy correction once I found it but a surprise because they were not how they had previously been set.

OK, here is an example of a .mov file with this clipping issue: (apparently I'm not allowed to post URLs, so this will take some minor decoding) www dropbox com/s/d0z92kjd9g8n30j/clipping%20example.mov. It's first prominent at "adapted" about 5 seconds in. It plays with no clipping in Firefox and Microsoft Edge on Windows, and also cleanly in Firefox, Safari, and Opera on OS X. It also sounds good in Quicktime Player and VLC on both platforms.

But it sounds terrible in Resolve (as well as avidemux and Audacity).

Adjusting the volume of the clip in Resolve does not reduce the clipping:

Before reducing volume:

After reducing volume:

I thought an easy work-around would be to extract the audio from a player that plays it back undistorted, but when I stripped the audio out using VLC (where it sounds fine as a .mov), the resulting waveform is still clipping.

The audio is encoded as MPEG AAC (mp4a). My best guess is that there is a "gain" multiplier value embedded in the audio header that increases or decreases the entire audio track volume (presumably to maximize dynamic range).

Some programs see that this value would cause clipping and reduce it so there is no clipping, others (like Resolve) interpret it literally and if that causes clipping, it clips. Or perhaps this gain value (which would lower track volume) is ignored by Resolve, and that is the problem.

If Resolve is interpreting this gain coefficient correctly, it's hard to say this is a problem with Resolve. But if Resolve is ignoring a gain coefficient, that should probably be considered a bug. Either way, changing Resolve so it would work better for rogue clips like this would save some users this headache.

In the end I declipped it in iZotope RX 7, which (while it worked amazingly well) is hardly an ideal or inexpensive solution solution for everyone.

Very interested in other people's thoughts on this - I could be completely off-base.

Update: Just upgraded to Resolve 17.1, problem is still present.

Now that I have upgraded posting privileges, here's a better link to the example:
https://www.dropbox.com/s/d0z92kjd9g8n30j/clipping%20example.mov

Watch/listen to it in your browser, then in Resolve.

It would appear that VLC and Windows Media Player are applying some processing such as clip recovery. If you display the VU meters they are hitting the top of the scale which means the signal is way to hot.
In the Quicktime Player the distortion is loud and clear, exactly the same as in Resolve. It is also evident if I convert the 44.1k audio to 48k with Shutter Encoder.
In Resolve the audio is certainly clipping hence the squared off waveform, and also the meters are rammed to the top. The audio has been recorded much to hot.

On my Mac, the audio sounds the same in VLC, QuickTime Player and Resolve 17.1.

I do have to turn the volume way down on VLC and QuickTime Player so as not to get blasted.

The VLC VU meters show lots of pegging, as Charles mentioned.

So aside from the clipped waveform display in Resolve, I don't see that it's doing anything worse to the audio than other apps.

In much earlier versions of Resolve, this type of clip would have played very distorted sounding audio. But that was addressed some time ago.