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Lame VBR to LAME CBR; Less frames, Shorter Time?!?
TheDogInBackyard
post Jan 19 2013, 01:20
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Hello guys,

Years ago i turned my cds to mp3, mostly in VBR. Now I'm cleaning my collection and re-doing the mp3s with 128kbps using the last version of lame. Tested the lame.exe and tested other apps thats uses lame. The result is always mp3s with a second shorter and less frames. I'm skipping something here? If you do a recode with 100 frames, you have an output with 100 frames? I'm wrong? And the output files is always using a lower values for replaygain... odd too...

Off-topic:
It's ok to use lame 64bit or it's better to stick with the safer 32bit?

Thanks.
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mjb2006
post Jan 20 2013, 15:51
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Here are some things to think about, things which affect the sample counts (sorry if you know this already):
  • The MP3 encoder adds junk samples to the beginning (encoder delay) and end (padding) of the MP3. This happens every time you encode.
  • The MP3 decoder adds even more junk samples to the beginning (decoder delay), and lags behind its input, so the same # of samples at the end will be unreachable—hence the need for padding.
  • The delay is consistent for each encoder, but padding varies with the length of the input and various esoteric factors.
  • VBR files encoded by LAME (3.12 and up) should have a VBR header (contains the string "XING"). CBR files encoded by LAME (3.94 and up) should also have a VBR header (contains the string "Info").
  • Info about the encoder delay & padding can be stored in the LAME tag (3.90 and up), which is embedded in the VBR header. A player can use the info to trim the junk samples from each end of the decoder's output.
  • If you use foobar2000 to "fix" a CBR file that has no VBR header, it will add a header with a fake LAME tag saying 0 padding and 0 delay, which is probably wrong.
  • Many players don't honor the LAME delay & padding values, and trim nothing, or just trim the decoder delay. Those that do trim encoder delay & padding, like foobar2000, usually don't handle low padding values as well as they could.

If you need to convert VBR to CBR, or vice-versa, it can be done without loss using MP3packer.
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