problem with AC3 in vegas

[John Rofrano]

[Nadia Yaghmour] “so, all of my avi’s encoded with 0x2000 (Dolby AC3) AC3 have problems working in sony vegas. some will either import with no sound, or the sound will take foorrreeeverrrr to build peaks, and even when i cancel it, it makes sony vegas get sooooo stuck and then ex out! i dont understand, i tried installing so many ac3 filters and codecs and nothing!!! i dont understand whats going wrong…”

What’s going wrong is that Vegas doesn’t support AC3 in an AVI container. Don’t bother doing it because it won’t read it properly. AC3 is a deliver format not an editing format. Vegas will tolerate AC3 from camcorder DVD’s but that’s about it.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Nadia Yaghmour]

seriously? well that sucks… but thanks, i’ll stop trying…

[John Rofrano]

Well the real question is where is this footage coming from, and can you deliver it in a more edit friendly format? Vegas will import AC3 for AVCHD files.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[Nadia Yaghmour]

well, no because they arent originally mine. its a tv show i downloaded, and i searched for foreeverr for some with mpeg audio layer and it was nowhere to be found…
oh, they import just fine, but the audio either doesnt work, or it will build the peaks soooooo slowly and then eventually freeze the whole program and ex out….

[John Force]

AC3 is a deliver format not an editing format.

Can you please explain this statement to me (I’m a moron)?
The reason I ask is because for the last 2 days I have been trying to accomplish what SHOULD BE (and probably is for non-morons) a simple task:

1-Import a 5.1 concert recorded on a DVD with my DVD/Hard-Drive TV recorder.
2-See all six audio tracks in Vegas Pro 10c (or other NLE’s mentioned below).
3-Edit the video only (cut commercials, add chapter markers, etc).
4-Render and burn back to a new DVD (without losing the 5.1).

I’ve tried this using Vegas Pro, VMSP 10, Premiere Pro, and Premiere Elements.
Some of my results:
1-I only see stereo tracks (rather than 5.1) on the timeline on import.
2-I only see stereo tracks (rather than 5.1) on the rendered file.
3-I get vague codec error messages using one NLE, but not another.

If I import a file properly (and see all the audio tracks), edit it, and render it as an NTSC DVD with 5.1 audio, will I see all the tracks when I look at the finished DVD in Vegas, or do the NLE’s “downmix” the 5.1 to a stereo track?
If they do downmix to a stereo track on the DVD, is the 5.1 info mixed in the track and decoded to 5.1 by my stereo equipment?
The reason I ask is because while fighting all of this, I created a 5.1 DVD (without seeing all the audio tracks on the timeline) using SVMSP 10, which I read does not encode 5.1, and the finished DVD sounds like a Dolby SS project (higher volume from the SS speaker when the audience claps, etc).

Also, I am familiar with exporting separate audio and video streams and using DVD Architect to create my DVD, but I don’t like following that procedure (no flames please!). I want to use “Create DVD” under the “Tools” menu like I do with all my other projects (I am fairly certain that I have used this procedure a few times in the past to edit my concert DVD’s without losing surround-sound, but I may be wrong).

Sorry for all the questions, but I am getting old and I’m getting confused trying to figure this stuff out!

Thanks for the help.

[John Rofrano]

[John Force] “AC3 is a deliver format not an editing format.

Can you please explain this statement to me (I’m a moron)?”

Video and audio data streams are quite large. Too large sometimes. The solution is to compress them into something smaller. The more you compress, the more information you loose about the original stream. Also if you compress it, you must decompress it to use it again. The software that preforms this COmpression and DECompression is called a CODEC.

There are codecs that are good for acquisition. These codecs usually are aimed at producing small file sizes using a interframe compression where not every whole frame is encoded. Instead, an occasional full frame is encoded and then only changes from previous frames are encoded. That makes the data stream smaller, but more work is required to decompress it because a single frame requires multiple frames around it to be decompressed and joined together in order to reconstruct the original frame.

Then there are codecs that are used for editing. These usually contain full frames using an intraframe codec. There are also digital intermediaries which aim to achieve lossless or near-lossless reproduction. These both eases the task of editing because only one frame needs to be processed to produce one frame of output.

Finally, there a codecs that are used for delivery which usually stress small file sizes again. They may also “color” the stream to make it look better or sound better on a particular delivery device (e.g., TV, Surround System, Radio, etc.)

Some formats work well for all of these, some are just good for one or the other.

AC3 is a delivery format which is highly compressed and actually applies profiles to the audio so that they sound good through your surround speakers. Once applied, the audio has been changed forever. You don’t want to reedit this audio and apply the profiles again and again and again. You want to edit the uncompressed source audio that is pristine.

Originally, no equipment would actually capture AC3 because it is not really high enough quality. Then camera manufacturers said, “What if we created a camera that recorded direct to DVD so people could just shoot and watch?” That’s when AC3 was used for acquisition only because the acquisition format was also the final delivery format. That doesn’t make AC3 suddenly good for acquisition or editing. It just means the camera manufacturers compromised quality for convenience. You should never buy one of these cameras if you plan to edit your footage. These are ‘shoot-n-watch’ cameras. (or as I like to call them, ‘soccer mom’ cameras)

AVCHD is like this too. It’s great for acquisition and delivery but horrible for editing. Do people still edit it? Yes. But it’s not the best editing experience. The best editing experience was good ole’ DV. DV used an intraframe codec (where every frame stands on it’s own) and 5:1 compression which made it good for acquisition, editing, and delivery. This spoiled everyone. One codec to rule them all! Then HD came about and you had 5x the data. Yikes! Now you need 5x the compression (25x) to maintain the same file size. That’s why interframe codecs that don’t store every frame are now used. They are a compromise and are good for acquisition and deliver but not editing.

I’m not sure if this explains it or confuses you more but feel free to ask more questions if it confuses.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[John Force]

John:
Thanks for taking the time to describe AC3.
But I still don’t know what I need to know:

Using Vegas Pro 10, or SVMSP 10, can I record a DVD (with a DVD/Hard Disk recorder) of a concert that plays back 5.1 surround sound from the DVD, can I edit the video portion (cutting commercials and the associated audio), and re-render it back from Vegas Pro or SVMSP10 to a DVD without losing the 5.1 surround sound?

If I then reimport the A/V from the DVD I just burned from the rendered file and look at the audio on the timeline using one of the above-mentioned NLE’s, will I see all 5.1 channels for the audio, or just two?

Thank you again for spending so much time helping so many people on this forum. You are truly an expert and a gentleman!

[John Force]

John:
I think I may have just found the answer (while looking at the SVMSP10 site):

Surround sound mixing and encoding
Import multichannel (5.1) source files from your camcorder including Sony® DVD and AVCHD Handycam® models. Use the surround sound mixing and panning tools to create surround DVD soundtracks. Encode AC-3 stereo or 5.1 mixes without leaving the software using the included Dolby® Digital AC-3 encoding software.

That is of course, if this applies to 5.1 imported from a DVD rather than a camcorder (that is mentioned in the paragraph).
What do you think?
Thanks again.

[John Rofrano]

[John Force] “That is of course, if this applies to 5.1 imported from a DVD rather than a camcorder (that is mentioned in the paragraph). What do you think?”

Yea, I was going to recommend that you change your project audio to 5.1 Surround Sound in the Audio tab of the Project Properties. Then use File | Import | DVD Camcorder Disc… and see if it imports the audio correctly.

~jr

http://www.johnrofrano.com
http://www.vasst.com

[John Force]

I’ll give it a try.
Again, thanks so much.