sound compression (128kbps ?) to achieve smallest file size

[juliusv]

Hi,

I would like to get as much video on on DVDR disc as possible. Those videos are cartoons (animated movies) for my kids. I don't want to let them "play" with the original DVD discs, so I decided to copy them. To save DVDR media and space, I'm trying to shrink every movie (usually 70min) to aproximatly 1GB, so 4 of them will fit on one DVDR. I'm using TMPGENC (2-pass variable bitrate) with average bitrate 1700kbps and half D1 (= D2) 352x576 (pal) video resolution. Video output is OK.

Next I would like to also "compress" the audio. Usually the .ac3 file is 100MB, and I can use it to:
1. Author DVD directly
2. Convert it to MP2 (leave standard setings (224 kbps CBR)) - output file .mp2 is little bit larger then AC3
3. Convert it to MP2 (change standard setings to 128 kbps CBR) - output file .mp2 is half size of .ac3 file (in this case 50MB)
4. ??? - any other ideas ?

So could you tell me if changing the bitrate of sound from 224kbps to 128 kbps will make the sound realy bad? Is it worth saving 200MB (4 movies time 50MB)? Or could I use VBR on sound bitrate?

My kids use cheap DVD player mustek and small SONY TV.

Or should I rather try to get 3 movies (instead of 4) on 1 DVDR disc, with original AC3 sound and higher average bitrate? (I guess it could be 2000kbps, but as I wrote before, 1600kbps is enought. In the begining I was thinking about VCD resolution 352x288 and VBR under 1000kbps, so I could get 8 movies on one DVDR disc)

Thanx for answers.

Julius

[tonofsteel]

I *think* from my readings in guides that AC3 is your best bet for file size. You talk about AC3 being 100MB, well what bitrate is that at??? You talk about comparing that AC3 file to different MP2 files, but what bitrate are you encoding AC3 at?

I think that 192 kbps AC3 is minimum for stereo material, but since your dropping the bit rate on the movies and cramming so much onto one DVD that dropping the audio lower than 192 for AC3 will not do any harm.....

[Shudder]

IMO the SLIGHT increase in video bitrate from dropping the audio will be barely noticeable, but the fairly drastic sound decrease will be prevalent throughout the entire video.

Maybe it's just me, but with slight pixelization/blocking I barely have any issues, but if sound is compressed too much I can't watch it.

[lordsmurf]

DO NOT let sound dip below 192k AC3 or 224k MP2 ... it will sound bad... very, very bad. You will start to clip audible sounds, not just inaudibles.

Those are minimums.

Use 256k to make it sound decent.

[thor300]

I have done an SVCD or 2 using 128kbps MP2, doesnt matter much for movies where its mostly talk and not so interesting music. For SVCD a 96kbps increase in video bitrate is noticeable in many cases.

[sacajaweeda]

128k is more than sufficient. Overkill for something as mundane as cartoon backups. Anything above 128k is lost on anybody not piping it through a high fidelity home theatre system, IMO. You won't hear the difference through those two inch speakers in your 27" TV.

[lordsmurf]

Cartoons have just as much audio fidelity, if not more, than live action.

You'll start to lose your upper registers and bass registers with 128k. The sound will be full of noisy junk. Screams, music, cars tire squeals, and high pitched voices (like children) will be destroyed. And I mean badly.

Only at 44.1hz was 128 possible, not 48hz on DVD. Even on a mono speaker on a 13-inch tv can I hear these things, and I'm not some audiophile. My 128k 44.1 MP3 sounds great. But MP2 and AC3 was never meant for such compression AND still sound good. Forget what you think you know about MP3, as it does not apply to DVD audio formats.

Video is the largest determination of space. Audio space is NOTHING compared to video space. If you need more space, cut down on the video resolution and bitrate. You can easily get 4 hours on a DVD with 2.5VBR 352x480 interlaced MPEG-2 with 192-256k audio.

I would call 128k AC3 "butchered" audio.

[sacajaweeda]

Well you're certainly entitled to your opinion. I will concede however that your dog could probably tell the difference in 128k audio on cheap TV speakers, even though you can not.

[ZippyP.]

I'm with Lordsmurf on this one, and I only listen on the TV speakers.

[juliusv]

Thanx a lot for sharing your opinion on this one.

I think I will use lordsmurf's advice and leave the AC3 sound (192kbps) there as I have demuxed it from .vob files.

I calculated that if I would save 50% of audio space (and probably loose 50% of its quality), I would gain only 5,55% video space (and probably get only +5% video quality) (calculation: if 100MB audio is 100% than 50MB is 50%, and if 900MB video is 100% than 950MB is 105,55%, together always 1000MB)

In order to save some space and increase video bitrate, while using original AC3 audio, I decided to cut off the texts that are at the end of every movie (director, actors, animators, ...). They have zero value to my kids. (sometimes this part is 5min long!)

I have another question/problem:
I have demux one movie with vstrip into one m2v file, but it seems to be corrupt. It should be 74 min long, but TMPGenc and Classic media player show that it is 41sec long with just black screen. Is the file size (4 158 000 MB = 3,87GB) a problem?

Juliusv