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Archive for August, 2020

On video sync

I’m not one to use the phrase “blew my mind” but … no, I’m not going to use it today either. But I watched this video and was .. shocked.

INTRODUCTION

The precis of the video is that syncing music videos to the audio track is not as straightforward as it sounds. In an earlier video, John Hess shows that physchoacoustics tells us that the audio beat should precede the related video event by a few milliseconds. So video editors usually cut audio so it’s one frame AHEAD of the video event. BUT in this video he finds out that YouTube shifts the audio so that it’s one frame BEHIND the video!

So, does this mean we need to cut audio TWO frames before video? and what about Vimeo? And does H.264 vs ProRes make a difference here?

I wanted to find out.

METHOD

I made 3 videos in DaVinci Resolve using a simple drum beat and some still photos. One had the video cuts exactly on the beat, on had the cuts with the audio one frame behind the video, and another with the audio one frame ahead of the video. I then rendered these into both H.264 and ProRes and uploaded all of those to YouTube and Vimeo. I’m not going to link to these videos (sorry) because I screwed up a couple of things and that messes up the results if you don’t know what I did.

RESULTS

Before uploading I had a look at the files that came out of DaVinci Resolve – using Reaper. The synced ProRes file look perfectly synced, but in the H.264 file, the audo was about 40ms behind the video – about one frame at 25fps. I don’t think this is exclusively a Resolve issue as Hess noted similar results with Premiere Pro.

On YouTube that particular difference didn’t seem to manifest itself. But the files where the audio and video where exactly synced, the audio looks clearly delayed to my eyes. On Vimeo there was a very slight delay but only really visible if you’re looking for it.

With the files where the audio was ahead by one frame, the YouTube videos looked much better. There was still a slight delay in the audio but, like the Vimeo above, it was quite reasonable. On Vimeo the files looked precisely synced.

Now this might be down to me using 25fps, I do this because I’m in the UK and that’s the TV convention here but I wonder (and haven’t had time to test this) whether 30fps might be better (or worse) on YouTube, it being American.

CONCLUSION

For best sync on both YouTube and Vimeo, cut your video so that the audio is one frame ahead of the video. In other words, when cutting video to audio, make your video cuts one frame BEHIND the beat. On YouTube (at 25fps) it’ll look fine, and on Vimeo it’ll look great.

Of course cutting video to audio is a subjective process and sometimes you want to cut across the beat – be creative folks!

All tests done on a a 2019 i9 Macbook Pro running DaVinci Resolve Studio 16.2.6 on OS/X 10.15.6, with 350Mb/s internet connection, and watched using Mozilla Firefox 79 full-screen after waiting for all online processing to complete.

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Introducing Synth Natter

Synth Natter is a YouTube podcast started by Stuart Russell in which one of us talks to someone interesting in the world of synthesizers. We’ve done 2 1/2 episodes now (the first one was just an intro) and have guests lined up for several more, so hopefully we can make a ‘go-er’ of it.

The idea is to interview someone new every second week and to get people from as wide a variety of the field as possible – the world of synths is very varied and there are people doing a huge variety of things with them.

Episode 0 was just a very short introduction from my studio where we chat about the point of the project and I give a quick tour of my studio synths.

In episode 1, Stuart interviewed Leah Kardos from Kingston University about her Stylophone Orchestra and her charge of the Visconti Studio (and its Mellotron!) as well as playing a couple of tracks of hers.

In episode 2 I chatted to Annie Jamieson (AKA Dr Sonic the Curator) from the Science and Media Museum in Bradford about the collection of fascinating synths and other audio equipment in the collection there.

The next one is on Saturday 22nd August where Stuart will be interviewing Matthew Bourne. We moved the show from Sunday to Saturday to avoid clashes with some other programmes (that I can’t remember the names of).

Subscribe to Stuart’s YouTube channel to keep informed about upcoming episodes.

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