Please Help! How can I change the audio specs ONLY of an Xvid/AVI ??

[moiz]

Hello, I'm a newbie.

I've an AVI (Xvid) file of 801 MB, the video quality is very good but, the audio is excellent. I wanna downsize the file to less than 700 MB so that it can be saved in a CD-R.

According to AVI ReComp 1.4.4, a freeware, which I've recently downloaded, the video size of that file is 565 MB and the audio size is 231 MB. How can I reduce the audio size ONLY ??

Audio specs of the file are below...

Type: ac3
Bitrate: 384 kb/s
Bitrate mode: CBR
Channels: 5.1 (surround)
Sample rate: 48000 Hz

How to change the channels from 5.1 (surround) to 2 channels (stereo) along with the Bitrate and Bitrate mode from CBR to VBR or ABR (which one is better ??) ???

Thank you!
Peace.

[Baldrick]

You could also try avidemux, choose copy under video and under audio choose mp3 and output as a new avi.

[poisondeathray]

Just to clarify Baldrick's instructions, you have to downmix the audio to stereo:

1) open in avidemux

2) set video sidebar to "copy"

3) set audio sidebar to "mp3"

4) press "filters" under the audio section, in the mixer dropdown menu, select "stereo". You can press configure also, to choose your bitrate (audio filesize)

5) set format to "avi"

6) press save with extension (e.g. "myfile.avi")

[moiz]

I've just opened it in Avidemux and it says, "Packed Bitstream detected. Do you want me to unpack it? Yes or No."

What is packed bitstream?

Can I change the audio settings only in AutoGK or in SUPER ??

[moiz]

Oh I forgot to thank you guys!

Thank you very much!

[poisondeathray]

If this is for PC playback, it is not necessary to unpack it (click no)

I don't think you can change just the audio with autogk , not sure about super (you would have to re-encode the entire video also = quality loss)

[moiz]

Hey, which Audio compressor gives better quality? I mean on 192 kb/s whose sound quality at stereo would be better?

MP3 (LAME)
or
AAC (FAAC)
or
AC3 (Aften)
or
AC3 (lavc)

[moiz]

According to the Avidemux's Calculator, all 4 of the above mentioned Audio compressors @ 192 kb/s at stereo will take 115 MB in my file.

Same Bitrate. Stereo. And same file size !!!

How come? Will they also sound same? Can they be ranked in terms of quality?

[poisondeathray]

For a given bitrate, AAC will give the best quality, but it's not compatible in .avi container. You have to use .mkv or .mp4

In terms of better compression AAC > MP3 > AC3

Filesize = running time x bitrate ; so it's not surprising that if you use the same bitrate they will be the same size

You have to add both audio & video.

[moiz]

Will AAC be better than others @ 128 kb/s as well?

I won't mind changing the container to .mp4

In fact I'm now thinking about changing the codec to H.264
Will it bring the file size further down without affecting the quality?

[poisondeathray]

Will AAC be better than others @ 128 kb/s as well?

I won't mind changing the container to .mp4

In fact I'm now thinking about changing the codec to H.264
Will it bring the file size further down without affecting the quality?

For the audio (192kbps MP3 vs. 128kbps AAC) it's tough to say, do some tests and judge for yourself.

You will lose a bit of quality if you re-encode the video, because h264 is a lossy format (unless you use lossless mode, but filesize will increase a lot)

If you used the original source (ie. DVD or blu-ray), using h264 will be better than the XviD you have now at the same bitrate.

[moiz]

OK. I'm not touching the video or it's codec (Xvid)! File size: 565 MB

Will change the audio to 192 kbps AAC, as you said that it's better than MP3 and AC3. File size (would be): 115 MB

In total (audio + video) the file size would be just more than 680 MB, the issue of saving it in a CD-R is solved.

Now, the question is...

What effect would the change in container make on the video (Xvid) ??
And which container is better for PC playback with above settings, .mp4 or .mkv ??

[moiz]

Thanks a lot for your kind support!

[poisondeathray]

.mkv has more utility (supports more things), but overhead is slightly bigger (minimal, like a few kb)

Either should be fine for PC playback, .mp4 might be better for older/slower systems (again difference is minimal)

You can do test it out yourself - it only takes a few minutes since you are only re-encoding the audio.

[jagabo]

If you think you might ever want to play the video on a set-top Divx/DVD player you should use the AVI container and MP3 audio.

[moiz]

poisondeathray,

If this is the case then I'll test .mkv & .mp4 on my PC and will report back!
Thank you very very much for your help!

jagabo,

Hmmm... I'm not planing to play it on DivX/DVD player, only on PC.
Thank you for your concern.

[moiz]

Something is wrong with THE file whose audio has to be changed. When I press 'Save' button ---> Avidemux (Not responding) !!!

But Avidemux is working fine on other AVI files no matter what their audio or video codec is.

Anyways, I've used AVI ReComp for THAT file.

As far as the .mkv & .mp4 comparison is concerned, I tested them with 2 other files and I'm unable to find any difference, but, remember I'm a newbie!

Thank you!