AC3 sound & mpeg sound (file sizes / DVDlabpro)

[bgspoonz]

I used DVDlabpro to try and bring the overall size of a movie clip down.
I transcoded the original mpeg sound (.mpa elementary) to AC3, which uses the TMPG...AC3 plugin... but, the file size of the two is the exact same!
Also, I didn't up the bitrate of the AC3 either, the original is 192 and I chose 192 for the AC3...
Am I missing something? I thought the AC3 was supposed to be much smaller than the mpeg sound file....
Any clues, or did I not (obviously) do something/changes when doing the transcode?

(original) Audio : 7.80 MB, 192 Kbps, 48000 Hz, 2 channels, 0x50 = Mpeg-1 audio Layer 1,
(trans. AC3) Audio : 7.80 MB, 192 Kbps, 48000 Hz, 2 channels/Dolby

[reboot]

AC3 is relatively the same size as mp2. You did nothing wrong.
Both AC3 and mp2 are smaller than PCM wav.
If you need to bring file sizes down, you can either cut the end off the video, author anyhow then use DVDShrink, or re-encode the whole video.

[bgspoonz]

yea, Im aware of 'shrinking' it down...but i thought that ac3 was supposed to be just a fraction of mpeg/LPCM sound size?

edit : by the way, ur guides are righteous!

[jimmalenko]

LPCM is the big one - MP2 and AC3 are roughly the same. THe files are the same size because you used the same bitrate

[bgspoonz]

ok... understood... now really wondering whats the 'real' purpose for ac3?
I tried this mpeg 2 AC3 sound transcode because I have a dvd that a friend gave me it was originally 6 gigs... he got it all the way to 1.3 gigs and there is no pixel. at all! But it did have ac3.... there is not that much dvdshrink in the world!

[yoda313]

Hello,

now really wondering whats the 'real' purpose for ac3?

Simple - its the DVD standard

Kevin

[bgspoonz]

Hello,

now really wondering whats the 'real' purpose for ac3?

Simple - its the DVD standard

Kevin

now, really wondering why with all the audio synch problems compared to mpeg/.mpa or LPCM working so well and less audio problems!

[guns1inger]

The sync issues come from the fact that LPCM and mpeg-2 encoders can be done without license, and the code to do it is well known. AC3 on the other hand needs to be licensed, and the most common encoders are not licensed, and are not necessarily 100% compliant. The other culprit is VBR mp3, which plays ok, but most encoders don't handle well. Always convert vbr mp3 to lpcm before encoding to AC3.

[bgspoonz]

The sync issues come from the fact that LPCM and mpeg-2 encoders can be done without license, and the code to do it is well known. AC3 on the other hand needs to be licensed, and the most common encoders are not licensed, and are not necessarily 100% compliant. The other culprit is VBR mp3, which plays ok, but most encoders don't handle well. Always convert vbr mp3 to lpcm before encoding to AC3.

VERY GOOD nfo! Thanks! Knew about the AC3 licensing...but didnt know about the vbr mp3 to AC3 probs! Will check into this, not to negate you...just love to find and apply good knowledge!