AC3 Joining

[EpheMeroN]

I captured a video stream that had AC3 audio, but I missed the first 3 minutes of the program. A friend captured it too with the first 3 minutes intact. I know I can join the video together using AviSynth, but is there a way I can merge the 2 AC3 files without having to do a re-encode? I just want to cut AC3 #1 where I need it, and then join AC3 #1 with my AC3 #2.

[tebasuna51]

Use BeSplit to cut and join.
For cut you can use DelayCut if your ac3 is 48 KHz.
For join you can use:
copy /B 1.ac3 + 2.ac3 New.ac3
Read the FAQ.

[XIII]

Look Here

http://forum.doom9.org/showthread.php?t=103416


XIII

[EpheMeroN]

Okay I have BeSplit v0.9 b6, but how can I trim AC3-1 before joining it with AC3-2? I need to trim AC3-1 at frame 5404.

[setarip_old]

@EpheMeroN

For my personal insight only, with no offense intended, would you please explain why you feel comfortable in using the first three minutes of your friend's video (and going through the effort of properly/synchronously joining it to your incomplete file), rather than simply accepting the entirety of your friend's copy?

It's just that I'm at a loss to understand what, if any, ethical/legal difference is involved in the two options...

[EpheMeroN]

Sure. I have no problem explaining. You see, my friend and I both had the same original source, but he converted his to an HR HDTV AVI while I want to make a DVD out of it. So the reason why I want to use his first 3 minutes and then splice that with mine, is because mine is of higher quality as he only has the AVI. He already deleted the source files.

[tebasuna51]

1) BeSplit work with time not frame. Your 5404 frame, is ac3 frame or video frame?
For ac3 frame (each ac3 frame 48 KHz = 32 ms): t = 5404*0.032 = 172.928
For video frame (the example is for PAL 25 fps): t = 5404/fps = 216.16
Then the command line for BeSplit (use your paths and calculated t):
Besplit -core( -input g:\ac3_1.ac3 -prefix g:\s -type ac3 -a ) -split( 0 t )

2) You say the ac3_2 is higher quality than ac3_1. I doubt any authoring DVD software accept an ac3 stream with two parts with different quality. At last you must reencode the first part with same parameters than part 2 (bitrate, samplerate, num channels, ...).

3) To join the ac3's you can use:
copy /B new_1.ac3 + ac3_2.ac3 full.ac3

[EpheMeroN]

Frame 5404 referred to the video. The video was 23.976 NTSC. And even though the 2 different videos are of different quality, the audio is the same. My friend muxed his AVI with the original 384kbps AC3 and that is what I have too.

[EpheMeroN]

Although both AC3 files are 384kbps, the volume in AC3 #1 is slightly lower than in AC3 #2.

Are there any free tools that can analyze both AC3 files, and tell me the difference in dB so I can amplify AC3 #1 to match the volume of AC3 #2?

[EpheMeroN]

... and if there aren't any, is there a way I could just amplify an ac3 file a few dB and nothing else?