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Ask Slashdot: Synchronizing Sound With Video, Using Open Source?

Posted by timothy on from the speed-of-sound-vs-speed-of-light dept.

An anonymous reader writes: I have a decent video camera, but it lacks a terminal for using an external mic. However, I have a comparatively good audio recorder. What I'd like to do is "automagically" synchronize sound recorded on the audio recorder with video taken on the video camera, using Free / Open Source software on Linux, so I can dump in the files from each, hit "Go," and in the end I get my video, synched with the separately recorded audio, in some sane file format. This seems simple, but maybe it isn't: the 800-pound gorilla in the room is PluralEyes, which evidently lots of people pay $200 for --and which doesn't have a Linux version. Partly this is that I'm cheap, partly it's that I like open source software for being open source, and partly it's that I already use Linux as my usual desktop, and resent needing to switch OS to do what seems intuitively to be a simple task. (It seems like something VLC would do, considering its Swiss-Army-Knife approach, but after pulling down all the menus I could find, I don't think that's the case.) I don't see this feature in any of the Open Source video editing programs, so as a fallback question for anyone who's using LiVES, KDEnlive, or other free/Free option, do you have a useful workflow for synching up externally recorded sound? I'd be happy even to find a simple solution that's merely gratis rather than Free, as long as it runs on Ubuntu.

12 of 103 comments (clear)

  1. A Clapboard by Anonymous Coward · · Score: 4, Informative

    What you want is a simple Hollywood style clapboard. Use any two track + video editor and visually line up the audio spike to the video frame where the board is closed.

    1. Re:A Clapboard by cayenne8 · · Score: 4, Informative
      Yep, the good old fashioned way of doing this is looking for the "CLAP" on the waveform and lining it up with the video.

      However, if you want something very polshed and fancy and automatic....take a look at Davinci Resolve 12 Beta.

      This is the free version that contains about 98% of the $1K paid version...what's missing likely you won't miss either....it is now a full blow NLE that compete with Premier and FCPX and others...

      You can do some amazing sync'ing of multi-clip video and sound with this thing..take a look at the demos on site.

      Unfortunatley, the Linux version is only available for Paid version, but hell, who doesn't have a mac or windows box laying around? I mean, if you have money for a decent video set up, you've already poured out some decent cash (camera, lights, software....hell, lenses ALONE)....surely you have laying around a win/osx box or can buy one.

      But, do give Davinci Resolve 12 a look...they also have out Fusion, which is IMHO, going to be a competitor to Adobe After Effects too for SPFX....worth looking into too.

      --
      Light travels faster than sound. This is why some people appear bright until you hear them speak.........
  2. Clap Clap Clap by lars3232 · · Score: 4, Informative

    That is what the movie claps you see in documentaries are for. You produce a clap with your hand, resulting in a spike in your external mic and in the video cameras mic. That way, you know where to sync the two in your favorite video editing tool and you're fine. No need for special software or something similar.

  3. Sorry but you are screwed by Sycraft-fu · · Score: 2, Informative

    Unless the devices themselves have some kind of common sync like wordclock or the like, they will drift out of sync. So sync the audio at any given point, it'll be out of sync later. That's why studios have all kind of gear to slave everything to a master clock.

    So you either have to have something that can do an advanced auto-sync and make sure the sync gets corrected in multiple places, or you'll need to do it manually. Depending on how long the recording is that may not be too bad and you may not need to adjust it that many times, but it is really all you can do.

    Now of course if you gear has some kind of clock input and output you can slave it together, but I'm guessing it doesn't.

    Finally your request for Linux stuff makes it really hard. The Linux video editing scene is, well, really really bad. There are no good tools that I've come across. GRanted I haven't looked in awhile but last time I did all I found were things that were incomplete, or buggy, or not very useful (or all 3).

    Something like Sony Vegas Movie Studio would do the trick and make it pretty easy to do what you needed manually, but it does cost money and isn't for Linux.

    1. Re:Sorry but you are screwed by Anonymous Coward · · Score: 0, Informative

      This is not correct.

    2. Re:Sorry but you are screwed by Anonymous Coward · · Score: 3, Informative

      He is correct. AV is my job, and I do a lot of it on Linux.

      My multi-track audio recorder and my video claim to run at the same speed - but there is variance between any two clock sources that are not linked.

      I use Harrison Mixbus (an excellent Linux/Mac/Windows DAW) and XJAdeo, both slaved to the Jack clock. You can shuttle audio and the video tracks your position according to the audio elapsed time.

      The two clocks drift apart very slowly. For the purposes of syncing live music footage, you only need to make a small correction to the audio every five minutes or so to keep things together.

      If you don't want to pay for Mixbus, you can use Ardour - it's getting very useable these days.

  4. Open Broadcaster Software by JohnnyComeLately · · Score: 4, Informative

    Your issue is very similar to what Twitch streamers go through with delay between audio and video. I'd suggest checking out OBS and there are quite a few how-to videos on YouTube to show you how to sync.

  5. Sync to the audio by linuxwrangler · · Score: 5, Informative

    Don't sync to the video, sync to the audio. Your video recorder records the audio "reference" track and you just sync your externally recorded audio to the reference track. Kdenlive has this feature. Other editors may a well.

    --

    ~~~~~~~
    "You are not remembered for doing what is expected of you." - Atul Chitnis
    1. Re:Sync to the audio by Fone626 · · Score: 5, Informative

      The above is totally correct, I use a separate recorder all the time so that I get better quality audio than my video recorder will supply, and then use Kdenlive to align the audio to the camera's reference audio.

      I've actually made a video that includes how to do it (among other features), and the video itself uses the Align Audio to Reference feature:
      https://www.youtube.com/watch?v=eIO73t228k0

      Here's a short text version:
      https://userbase.kde.org/Kdenlive/Manual/Timeline/Right_Click_Menu

  6. mencoder by carlhaagen · · Score: 4, Informative

    mencoder will do exactly what you need, muxing separate video and audio tracks into one container file of your choice, with tunable offsets for each track.

  7. A/V sync command line by mungewell · · Score: 5, Informative
    I had a recent project which needed to sync Audio from recorder with video from several cameras. I found this project on GitHub which has a command line tool to measure the delta between the high quality audio from recorder and the low quality from the cameras, and then I could just put this offset in my video editor when inserting the clips.

    https://github.com/allisonnico...

  8. I'm not sure about doing it live, but... by waspleg · · Score: 3, Informative

    I use avidemux and audacity to add Rifftrax to movies. Basically copying out the existing audio, merging the rifftrack with the movie audio in to one track and then putting it back in as a separate audio track so the original audio is there too if you want to watch the movie without jokes (pretty rare for me actually, but it's nice to have options ;)).

    Someone else already suggested OBS, I've used that too for recording gaming video. It can be pretty intensive and it takes some fiddling to make it workable but it's not bad.