Topic: new audio/video synch method?

[dklein]

I think I posted before about extracting the crappy camera audio and putting it in multitrack so you could line up the good audio (separately recorded).  Match and mux the good audio.  But then there's the time drift issue which also needs correction by stretch or cut.

I had a thought - just wanted to do a reality check here.  My audio is 44.1 so I automatically need to resample to 48k for a DVD.  My audio is ~700ms/hour longer than the audio extracted from the camera.  Rather than stretching or cutting it up, I calculated a resampling rate that will return the audio speed to the camera speed.  The approach is to resample to a non-standard sample rate that will yield the proper length if the header is set to 48k.

For my camera...

1.  Resample from 44,100 to 47,090 (this is an actual conversion - I just specifiied the rate instead of using 48k)
     - at the end of this step the audio is the same length (at a sample rate of 47,090)
2.  Set sample rate to 48k (no processing)
     - the audio instantly becomes shorter as more samples are eaten up per second

This essentially speeds up my audio by 720 milliseconds per hour and matches the camera within 20 ms (a cut or two can fix that).  Whaddya think?

I figure I had to resample anyways, at least there's no additional processing.  It'll give better synch than doing cuts because the drift is significant (there's 60ms of drift on by the end of a 5 minute song).

There should be some pitch change from this method but it is sooooo small I can't even tell if I flip back and forth between them (it's a 0.02% pitch change).

[firmdragon]

yep that should work.

this is pretty similar:
http://www.videohelp.com/forum/userguides/140540.php

[Ed.]

i'm working on a grandaddy video right now where someone else mastered the video and put two sources together, only when he sent me the tape it didn't have any audio on it.  so i'm trying to go thru and match it up without an audio track to synch it to.  VERY DIFFICULT.

i've got the beginning matched up but slowly over time it gets out of synch, the audio is already 48k, so i don't think i could do the resampling, right now i'm planning on stretching the audio a little bit between songs here and there when there isn't much sound.

gonna take awhile, but it'll be worth it in the long run i guess.

[dklein]

this is pretty similar:
http://www.videohelp.com/forum/userguides/140540.php

yup - thanks.  Some of the video guys don't seem to care a ton about sound (note the last step - letting tmpg convert to mp2  )

[hyperplane]

i'm working on a grandaddy video right now where someone else mastered the video and put two sources together, only when he sent me the tape it didn't have any audio on it.  so i'm trying to go thru and match it up without an audio track to synch it to.  VERY DIFFICULT.

i've got the beginning matched up but slowly over time it gets out of synch, the audio is already 48k, so i don't think i could do the resampling, right now i'm planning on stretching the audio a little bit between songs here and there when there isn't much sound.

gonna take awhile, but it'll be worth it in the long run i guess.

i've done one video that didn't have any sound to begin with, and synchronized a DAT audio source to it. it is a big pain. luckily for me, once i lined up the WAV file at the beginning, it stayed synchronized throughout the ~100 minute show. (so happy both audio and video sources were taped digitally and they were the same length.)

one trick for synchronizing audio to a video source with no sound is to watch for the drummer's stick to make contact with his kits. if the audio source is pretty decent and the drums are clear, then it can make editing life a lot easier!

in general, as for encoding to MP2: don't do it! AC3 if you must, or go flat out with L/PCM (uncompressed WAV) audio. with the right software, it's not difficult to be frame accurate in splitting up the video onto 2 DVDs so you can fit the PCM audio track on the discs.

[dklein]

Anyone ever use R8Brain for resampling?  It looks good - you can specifiy the sample rate right down to decimals and there's a separate box for setting the header.  It's designed exactly for the purpose.  I've got a job running now - we'll see if it sounds good.

Here's the site http://www.voxengo.com/r8brain/
You may have to check the google cache - looks like they've exceeded their bandwidth for the day
There are lots of places with the download (as you'll see when you google)

[spyder9]

If you guys want, I can have my buddy, Mattman, add his 2 cents to this thread.  He's a real pro.  He releases most of the Dead DVD stuff that's out on the net.  We have collaborated on a bunch of Tape > DVD projects.  I do the video conversion and he does the audio synch.  He has his thing down to a 2 hour process.  He usually sews in SBD audio.  But, he has done AUD patch work as well.  Clean.  We're currently working on some Dead Europe '90 tape conversions.

[dklein]

love to hear what he has to say.  In 2 hours I can't get shit done!

[eman]

I am a total n00b in vid, and I am going through the phase where I find out that there aren't many cameras that take line in (while shooting) $500. The alternative is to record audio and sync later- this thread is the first time I've seen that DVD requires 48kHz. Yes? So if I am recording with the intention of syncing later, then record at 48?
More questions later.
Eric

[firmdragon]

yeah that woudl make making dvds easier. dvds are 48khz

[hyperplane]

well, you can record at 32 kHz - which is also within DVD specifications. but obviously, that will lower the sound quality. or you can record at 44.1, but then you'll have to upsample to 48 or downsample to 32.

i always record at 48k anyway, and it just saves me that extra time of resampling later on when i do a DVD mix. (and for audio tapes that i don't have a video source for, i still can easily make DVD discs with the 48k audio and have the full show + opener/s on one disc. pretty sweet stuff!)

so yes, if it's possible, then try to tape at 48k if you're planning on creating a DVD with your audio source.

[Dr.FOB]

in general, as for encoding to MP2: don't do it! AC3 if you must, or go flat out with L/PCM (uncompressed WAV) audio. with the right software, it's not difficult to be frame accurate in splitting up the video onto 2 DVDs so you can fit the PCM audio track on the discs.

Any rough idea of the video time to fill a DVD when mux'ing L/PCM? ~1hr?
Rendering takes too long to miss by much...

[hyperplane]

Dr.FOB - it depends on how much video you want on the disc. if you feel the quality is ok at an average video bitrate of 5000 (a.k.a. 5 Mb/s), then you can squeeze right at 90 minutes of video with PCM audio onto 1 DVDR... and have about 100 MB left of space on the disc. and from what i've read, it's a good idea to have a good 100 MB or so of "empty space" left on the disc, because some DVD burners have problems burning right to the edge of the disc.

if you want the optimal video quality go with 7000 to 7500 for the average video bitrate, and PCM audio. with the average video bitrate at 7000 and PCM audio, you can fit right at 69 minutes on 1 DVDR, and at great quality (where the DVDR quality is so well-preserved that it's tough to differentiate between the DV .AVI file and the DVDR). i've created several hundred DVDRs, and done side-by-side comparisons with the quality of the DVDR vs. original source (often VHS, or a DV cam source), and they look virtually identical. especially for a VHS source, it's extremely well preserved - and can often be even better than the VHS tape looks, if you learn a little and use some filters to "clean up" the video.

[bootray]

I am in a similar spot as you..
I have this nice DVD of Stevie Ray Vaughan at the
Iowa St Fairgrounds in D.M. Iowa with crummy sounding audio.
Not to worry as I have a killer Audience Master recording
and I want to combine the two.
I start by Demuxing the DVD into a .m2v video and a .Ac3 of the crummy audio.
Next I import the .m2v file and a .wav file of my master recording into
adobe premier as the primary Vid & Audio.
I align the tracks at the start only to discover there is a timing
problem and the sync goes out. Video running long.
I figure I will adjust the length of the video to suit the audio since
it was recorded on a sony tcd5m w/ servo control capstan and I think
it is accurate in pitch.
I adjust the vid legnth so it syncs towards the end of the audio, only
to find the sync spot at the start has shifted. Still out of sync...
At this point I load the crummy ac3 audio and the .wav master recording
together for time comparison and discover they are similarly out of sync,
with the crummy audio (and Vid) running slower than the .wav audio replacement track.
The .wav was, 16/44 bit converted by premier to 24/48.
I concidered syncing after every track rather than over the entire legnth
of the clip...
This will be sweet when it is done but I need advice on the tech.
thanx you all.
Ray in DM

Wont be back till monday
thanx again...

[BLOODYJACK]

Record the audio separate and sync later. Why would you want anything less than the best audio on a DVD?
I just let the camera record with its mic and use its wave data in the editor to eyeball with the jb3 audio file. After you get close pan one track hard left and the other hard right and tweak by ear.