Annoying problem, Re: Merging AC3s...

[takearushfan]

Hey all,
I have 17 AC3s. I don't want any video. All I'm trying to do is merge one after the next, to make a continuous AC3. Yep, I've tried looking for the answer but haven't found it, hence my asking here.
Thanks,
Justin

[AlanHK]

If you can handle command lines, see http://ubuntuforums.org/showthread.php?t=1695477

[takearushfan]

Sometimes I am comfortable with command lines, but I'm not sure how to interpret the link you provided.

[AlanHK]

It tells you how to do it with ffmpeg or mencoder.
mencoder looks the most promising.

[FaeGiN]

https://forum.videohelp.com/threads/213080-Join-AC3-files

[Trippedout]

just tryed it out in winavi you can join them under video file in all in one converter then under common audiofiles you can output them back to ac3 it allows you to do that when you add the files you need to go to advanced and change to output to single file yes for instance i out put the ac3 files as mpg then back to ac3 in winavi all in one

[Cornucopia]

One of the cardinal rules of joining files is: All segments in a join must have the same format specifications (resolution, bit depth, sample rate, etc) for it to work correctly.
Reason: Almost NO multimedia container formats have the capacity for documenting the multiple, disparate info needed by conjoined differently formatted segments (Quicktime Playlist/Reference files excepted).*

The way it usually works is that a container has Header metadata info, then the Media Essence payload tracks (usually interleaved for parsing & buffering efficiciency), and then optional Footer metadata. So a typical MM file looks like this:

H.H.V1.V1.V1.A1.V1.V1.V1.A1.V1.V1.V1.A1.V1.V1.V1.A1.V1.V1.V1.A1.F.F.

If you JOIN the quick & dirty (and bad) way, using "copy /b", you end up with a joined file that looks like this:

H.H.V1.V1.V1.A1.V1.V1.V1.A1.F.F.H.H.V2.V2.V2.A2.V2.V2.V2.A2.F.F.H.H.V3.V3.V3.A3.V3.V3.V3.A3.F.F.

The problem with that is that those later Headers & Footers wouldn't exist in a legit copy of a combined multimedia file, and according to the specs, decoders & parsers would expect to look there for them and would ignore that information. They could ignore ANYTHING past the 1st Footer, in which case you are screwed as your joining is a waste of time. Or, they could ignore the subsequent Headers & Footers. This would be the equivalent of a legit join or a file combined in an NLE, which would look like this:

H.H.V1.V1.V1.A1.V1.V1.V1.A1.V2.V2.V2.A2.V2.V2.V2.A2.V3.V3.V3.A3.V3.V3.V3.A3.F.F.

The problem with that is that of course you now ONLY have ONE header section. So everything is decoded according to that one set of metadata.

Which is why that cardinal rule exists!

*What can sometimes work is if there is metadata info encapsulated WITHIN one of the elementary streams (V or A), but then interpretation is still left up to the decoder/player. This usually only seems to work consistently WRT bitrates (as that is often expected to vary with a stream).

Scott

[FaeGiN]

@Cornucopia Doesn't AC3fix or another tool fix those Header discontinuities...? I mean is it not possible to do the old way of copy /b and then run it through a utility? I never tried it but just found a few advising it...do you know?

[Cornucopia]

Don't know. Possibly. Could tell with a hex or atom viewer.
But that still won't help if the segments don't already match in their settings.

The point I'm trying to make is that if you have to go to the trouble of joining and then fixing and then comparing, etc, it actually makes more sense to instead use the correct tool all along: a smart-rendering NLE. (which basically internally does all those things for you)

Scott

[aedipuss]

convert them all to pcm wav then join.