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-   -   BBMpeg: Output file size not changing when using lower bitrate audio (http://www.digitalfaq.com/archives/encode/748-bbmpeg-output-file.html)

gvarney 07-27-2002 06:44 PM

Output file size not changing when using lower bitrate audio
 
Hi,
I have encoded a capture of The Deer Hunter at 29.97fps in TMPGEnc with the KVCD Plus 352x480 template. I tried muxing the first 94+ minutes with bbMPEG using the DVD2AVI generated MPA file at 224kbps. It came out to 836MB, a little too large. So I used HeadAC3he to re-encode the audio as MP2 to 192kbps. Also did a conversion to 160kbps. Well, with either the original 224 or even 160 the final movie file size is the same, or within a few bytes :roll: . What's going on? I am *not* selecting to pad the VCD audio either. Here are the last few lines of the bbMPEG logs for each, adding the file size:

With 224kbps audio:

Multiplexing information
Video stream data rate : 321900 bytes/sec (2575200 bits/sec)
Audio stream 1 data rate : 28000 bytes/sec (224000 bits/sec)
Overhead data rate : 4600 bytes/sec (36800 bits/sec)
Total data rate : 354500 bytes/sec (2836000 bits/sec)

Multiplexing file e:\capture\the deer hunter00.mpg
Finished multiplexing e:\capture\the deer hunter00.mpg

Final file size: 836,206KB

With 160kbps audio:
Multiplexing information
Video stream data rate : 321900 bytes/sec (2575200 bits/sec)
Audio stream 1 data rate : 20000 bytes/sec (160000 bits/sec)
Overhead data rate : 4500 bytes/sec (36000 bits/sec)
Total data rate : 346400 bytes/sec (2771200 bits/sec)

Multiplexing file e:\capture\the deer hunter00.mpg
Finished multiplexing e:\capture\the deer hunter00.mpg

Final file size: 836,289KB

Any ideas??

Thanks,
Geoff

kwag 07-27-2002 07:41 PM

Re: Output file size not changing when using lower bitrate a
 
Quote:

Originally Posted by gvarney
Hi,


Final file size: 836,289KB

Any ideas??

Thanks,
Geoff

Yes. You didn't IVTC your capture.

-kwag

gvarney 07-27-2002 08:17 PM

Re: Output file size not changing when using lower bitrate a
 
Quote:

Originally Posted by kwag
Quote:

Originally Posted by gvarney
Hi,


Final file size: 836,289KB

Any ideas??

Thanks,
Geoff

Yes. You didn't IVTC your capture.

-kwag

Kwag,
Yeah, but that was intentional. I can't use 24fps with my Apex, so I encoded at 29.97fps. How is it possible that muxing the same video (m1v) with 2 different sized audio files can come out to so close to the same size? I shoulda been able to reduce the size by at least 20-30MB or something with 160kbps audio.

Maybe I'm not understanding something. The file size itself (over 800MB) isn't the problem, it's that I can't decrease it by reducing the audio bitrate.

Geoff

kwag 07-27-2002 11:25 PM

Re: Output file size not changing when using lower bitrate a
 
Quote:

Originally Posted by gvarney
Quote:

Originally Posted by kwag
Quote:

Originally Posted by gvarney
Hi,


Final file size: 836,289KB

Any ideas??

Thanks,
Geoff

Yes. You didn't IVTC your capture.

-kwag

Kwag,
Yeah, but that was intentional. I can't use 24fps with my Apex, so I encoded at 29.97fps. How is it possible that muxing the same video (m1v) with 2 different sized audio files can come out to so close to the same size? I shoulda been able to reduce the size by at least 20-30MB or something with 160kbps audio.

Maybe I'm not understanding something. The file size itself (over 800MB) isn't the problem, it's that I can't decrease it by reducing the audio bitrate.

Geoff

I think something is being padded in there. How did you mux the files. As VCD or SVCD?.

-kwag

gvarney 07-28-2002 10:34 PM

Re: Output file size not changing when using lower bitrate a
 
Quote:

Originally Posted by kwag
I think something is being padded in there. How did you mux the files. As VCD or SVCD?.

-kwag

As VCD, VBR, set the mux rate to 0. Everything else is left alone as is. Weird.

Geoff

UPDATE
Umm... I think I figured this out... I was (unnecessarily) entering a setting in the SIZE for the bbMPEG general settings (like 817MB) so this was maxing out. I really thought that the video size (with no audio) was coming in at a size low enough that I could add some audio to make the 800MB (plus overburn). Well, I guess I did something wrong.... I set that to zero, size came out above 900MB.

Geez! Well, at least I "figured it out". :oops: :oops: :oops: :oops: :roll:


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