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Matching sound to video

This is relevant to aviation videos, and to the difficulty of recording sound on a camera which is externally mounted.

Let’s say I have a video camera and I start/stop it as required i.e. the video is not continuous.

No sound recorded.

The sound track is recorded on a separate device, in the cockpit, but that recorder is running all the time, nonstop.

Is there some automated way to extract the relevant bits of the sound track and add them to the finished (post edited) video? It would mean recording a digital time track onto the audio, obviously. What sort of recorder would be suitable?

Is it possible to do this with .mp4 video? I read a claim by Sony that only the higher bit rate formats (XAVC) support this kind of stuff but I can’t see why since mp4 clearly has time recorded inside it too.

Administrator
Shoreham EGKA, United Kingdom

I’m not sure this is what you’re looking for but the very low-tech way I do it is to tap the microphone on my headset so that the camera can see it when I start recording the video. Like this I can align it later on in video editing.

Definitely not the most elegant solution in the world but given the precision required to get this right I’m not sure embedding time in video could really ever work.

LFLP/LSGL

That’s clever

I think the “pros” use some kind of digital sound recorder and then some “software” pulls out the corresponding sound track fragments which correspond to (what is left of, after editing) the video track.

One needs a fairly automated process because most aviation videos need masses of stuff removed – probably 95+%.

Administrator
Shoreham EGKA, United Kingdom

That’s what the clapper board is for…

When you restart the camera recording just do something that makes a simultaneous visual and loud audible cue (clap perhaps).

You can then just look at your audio file and find the peak and you know you’re at the start of the next video segment.

I’d be amazed if there was a way of automating this other than using a real timecode.

Google ‘LTC’ – this is a timecode represented as an audio signal. You can get a cheap generator and then run the signal into your camera and one channel of your audio recorder. Any decent video editing software will then be able to sync your tracks together.

That’s what the clapper board is for…

The problem is that with an externally mounted camera there isn’t anything I can do from inside the cockpit which will be picked up on the camera.

Doesn’t an mp3 audio track contain a timecode? Or is the time just the audio sample rate x the sample count from the start?

I wonder how the pro people do this e.g. when news reporting, when the camera is often far away and the reporter is recording onto a recorder they are carrying.

run the signal into your camera

That’s interesting – thanks. However that is another issue… the camera in question does have a sound input (“PLUG IN POWER” mike – the usual thing) but that is yet another cable to run. Also, while I have already modded the waterproof housing like this the mike input is at the base of the camera and cannot be accessed with the camera in the housing. And there is no way to record sound externally via wifi or (in cameras that support bluetooth) via bluetooth. The designers could have done so much more so easily…

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

The problem is that with an externally mounted camera there isn’t anything I can do from inside the cockpit which will be picked up on the camera.

If it’s just to add and sync some headset audio, wouldn’t a word and a wing rock be precise enough? I have the same problem syncing picture in picture, but there +/- 0.25 sec is close enough:


Glenswinton, SW Scotland, United Kingdom

That’s brilliant, Jacko. What software do you use for this?

Administrator
Shoreham EGKA, United Kingdom

I use this:
http://www.videosoftdev.com/free-video-editor
The developer says:
“The video editor is intended for editing video files and creating videos of any complexity involving various visual and audio effects. The program offers rich functionality and yet has a simple and intuitive interface, allowing you to create videos with a bare minimum of efforts.”
… which is rot, of course, because “videos of any complexity” are likely to need more than “a bare minimum of efforts”.

Glenswinton, SW Scotland, United Kingdom

I have probably now sidestepped this sync requirement.

The camera assembly I have built is autonomous for 10+ hrs ( here ) and I have a little £10 mp3 recorder which runs for about 100 hours at 64kbits/sec

Starting the camera and the recorder at the same time will take care of it.

Administrator
Shoreham EGKA, United Kingdom

A little update: the above “mp3 recorder” turned out to be a con. It may record to mp3 but the only way to get the data out is via analog playback from the headset socket! The USB socket is for power only. I bought a £20 one which turned out to be useless too, and now use a £80 Tascam DR-05 which works great, from a spare headset socket, via an attenuator pot.

But I now need a sound sync solution for longer flights, because the FDR-1000V camera, if used in one of the higher quality modes (50mbit/sec 1080P or any 4k mode), won’t outlast the longest possible flight. So it needs to be turned on or off.

I wonder why all these “timecode” solutions exist because surely mp3 contains a timecode already? I know video does and has done since Hi-8 (25+ years ago).

Administrator
Shoreham EGKA, United Kingdom
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