Need CBR MP3 in FFMPEG encode, can you help?

[RogerTango]

Here is the line I am using:
ffmpeg -i "input.avs" -vcodec libxvid -s 1280x720 -b 5500k -acodec libmp3lame -ab 128k -r 30 -ar 44100 -aspect 16:9 -g 20 -y -f avi "output.avi"

The arguments work FINE, but is yielding VBR MP3.

How can I modify my line to encode CBR MP3?

Thanks for any help,
Andrew

[AlanHK]

See http://lame.cvs.sourceforge.net/*checkout*/lame/lame/doc/html/switchs.html

* --cbr enforce use of constant bitrate
This switch enforces the use of constant bitrate encoding.

* --abr n average bitrate encoding
Turns on encoding with a targeted average bitrate of n kbits, allowing to use frames of different sizes. The allowed range of n is 8-310, you can use any integer value within that range.

* -b n bitrate

* -B n maximum VBR/ABR bitrate

So it looks like "-ab" is "average bitrate" (vbr).
If --cbr doesn't work try setting -b and/or -B instead of -ab

(Assuming these switches work the same in ffmpeg.)

PS: Where did you get a build of ffmpeg that supports Avisynth?
I see http://www.ffmpeg.org/faq.html#TOC28 says "If you have built FFmpeg with ./configure --enable-avisynth...."
But I don't want to try to roll my own.

[RogerTango]

The LAME switches are not valid in FFMPEG, the -AB switch is different, this is AudioBitrate.

The FFMPEG I have is the Win32 binary I download, I dont recall where, but it is r16596 Jan 14, 2009 build.

I *may* have to just do the vid in FFMPEG, the audio in LAME and then mux into AVI, I just wanted a "one stop solution".

Andrew

[AlanHK]

Are you sure that it's VBR?
According to this thread:
http://lists.mplayerhq.hu/pipermail/ffmpeg-user/2008-November/017719.html
it's really CBR, but flagged VBR in the header.

I found the ffmpeg included in Avanti supports Avisynth.

[RogerTango]

According to VirtualDub, the read AVI is reported to have a VBR MP3, I dont know if it is the header, or the entire MP3 segment is VBR.

I feel that a CBR should be marked as CBR, and VBR be marked as VBR. It almost seams to me to be illogical to generate a CBR audio and then header it as VBR.

I know a lot about video and audio, but when it gets to the headers, how it's used, manipulating it, etc.. Im no expert. This information is beyond my scope of needs, so I dont dive that far into the technical aspects.

UPDATE:
I just looked at the resulting AVI with MediaInfo, this is reported:
Bit rate mode : Constant
Bit rate : 128 Kbps

GSpot also reports it to be CBR.

It appears it *IS* CBR, but for some reason VDub is reading VBR...

This thread can be considered "closed", many thanks to Alan for your time and effort!

Andrew

[RogerTango]

I just had VirtualDubMod write a piece of the original AVI, using direct stream copy for both audio and video, and in the beginning when I loaded it it reported VBR, "Should I rewrite the header?", I told it no... Then used MediaInfo to look at the cropped AVI.. That *ALSO* shows CBR MP3 stream...

It looks like its more of a "problem" with VirtualDub... I dont think any other software has given me any problems.

Andrew

[AlanHK]

I just had VirtualDubMod write a piece of the original AVI, using direct stream copy for both audio and video, and in the beginning when I loaded it it reported VBR, "Should I rewrite the header?", I told it no... Then used MediaInfo to look at the cropped AVI.. That *ALSO* shows CBR MP3 stream...

In posts in the thread I linked people say that letting VDub rewrite the header fixes the (apparent) problem.

[Bonie81]

I would rather suggest use WinFF gui for FFMpeg with additional command line options for CBR.