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I have a few CDs lying around that I'd like to rip and encode in MP3 format using Rhythmbox. After installing the ubuntu-restricted-extras package, one of the options that shows up in Rhythmbox's preferences under "preferred format" is "CD Quality MP3," but from the encoder options it appears that it uses a constant bitrate.

I'd like to set up an Audio Profile to encode at a variable bitrate (VBR) at a reasonably high quality. What options do I need to use under "gstreamer pipeline?" Or alternatively, is there a more discoverable way to enter encoding options than entering command-line options into Rhythmbox?

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up vote 4 down vote accepted

Just so we're talking on the same page, the pipeline used by this encoding target looks like the following on my system:

audio/x-raw-int,rate=44100,channels=2 ! lamemp3enc name=enc target=0 quality=6 ! xingmux ! id3v2mux

You can learn about each of the elements in the pipeline with the gst-inspect-0.10 tool. For example, to learn about the MP3 encoder used here, you could run:

gst-inspect-0.10 lamemp3enc

Among other things, this will tell you about the various properties supported by the element and their defaults. This tells me:

  • encode using variable bit rate (cbr=false from defaults)
  • the encoder has been set to optimise for quality rather than a target bitrate (target=0)
  • uses a VBR quality setting of 6 (quality=6)
  • uses the standard quality of the LAME engine (encoding-engine-quality=standard from defaults)

So you should already be getting VBR output from that pipeline. If you want higher quality, lower the 'quality=' number (0-10, 0 is the highest quality) and perhaps add encoding-engine-quality=high.

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Awesome. Thanks for breaking it down for me. I'm not sure what my original pipeline was because I stupidly edited it instead of adding a new one, but it seemed to be CBR from reading it. Two small hitches in this answer though: 1) for LAME, lower numbers == better quality and 2) I had to restart Rhythmbox before my new Audio Profile showed up in the list. – Ryan Apr 17 '11 at 14:16

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