AC3 file same size as MP2 source file

[Mark Fredrickson]

I de-multiplexed my MPEG2 home video into MV2 and MP2 files, then ran AC3Machine (BSweet) to convert the MP2 to AC3 and the AC3 file size was almost exactly the same (205,071 kb for MP2 and 205,070 kb for AC3). The AC3Machine settings used were all unchecked except for Channels Mode set to Stereo. I thought that AC3 was more compressed than MP2 and I would gain some extra disk space for video if I used AC3. Was I wrong? If so, is there any reason to convert home video to AC3? I'm creating DVD's for all my home videos and the MPEG2 with MP2 plays ok on my DVD player.

[Tri]

Check your bitrate settings. They are most likely the same as your source mp2-file.

[Mark Fredrickson]

Yes they are - 224. But I thought that AC3 encoded at a higher compression therefore it would be smaller than MP2. Maybe I got that impression from other posts where people were encoding to AC3 but from PCM not MP2. In that case (PCM to AC3) you would see a difference, but not from MP2 to AC3? But it was interesting that the files were almost identical in size.

[KpeX]

Bitrate * length = filesize

Compression type or format has nothing to do with your filesize. You are better off staying with the MP2 source if your DVD player supports it because when transcoding from MP2 to AC3 you will lose quality. PCM is uncompressed audio so when encoding PCM there is no loss. MP2 and AC3 are both 'lossy' formats, so the less conversions you have to do, the better. hth,

[Mark Fredrickson]

Thank you. I will do that. Not converting to AC3 makes my job a lot easier (I have over 200 hours of home video I have to cut to DVD).

For passing these DVD's around to other family members and for the long term future, do you think that MPEG2/MP2 will be supported by the other main DVD player manufacturers?

[KpeX]

MPEG-2 Video is the only video format supported by DVD specifications. MP2 audio (Mpeg-1 Layer 2) is also supported under DVD specs but due to the fact that it is not commonly used some players do not support it. Personally I have not tested it on a wide range of players, perhaps someone else can chime in on if many players support MP2.

[fccHandler]

My understanding is that MP2 is required for PAL DVDs and AC-3 is optional. The situation is reversed for NTSC DVDs (AC-3 is required, and MP2 is optional). So, technically an NTSC DVD player need not support MP2, but it's likely that it does if it can play VCDs.

[echooff]

I own 4 different brands of dvd players here in Florida. All of them play mp2 with no problem. I have made a number of dvds from home video and set them to relatives as far north as New Hampshire and as far west as California. All report the dvds work. The only time I use ac3 anymore is if the original source is ac3 (rip a dvd). Other than that mp2 works for me. However, my understanding is to be NTSC compliant a Dvd must have ac3 or pcm audio.