VBR transcoding

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VBR transcoding

Postby crisbtreets » Wed Jul 12, 2006 9:31 pm

I noticed a note in the Max Bitrate Help button that said only constant bitrate files can be resampled. Also noticed in the log that not every file was being resampled. Why is this? I happen to have mostly VBR mp3 files. Is there a change I can make to support VBR files? Thanks.
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Postby sindre_mehus » Thu Jul 13, 2006 6:46 am

I have good news for you! Subsonic 2.8 will support resampling of VBR files. (Well, at least VBR files with a XING header.)

The problem with MP3 VBR is that there is no way to find the average bitrate except from reading all the MP3 frame headers. (We need to know the average bitrate in order to determine whether downsampling is required). Reading the entire file would be too slow.

To overcome this limitation, some (most?) MP3 encoders adds a special proprietary XING header to the MP3 file. The average bitrate can be found in this header.

As of Subsonic 2.8 the XING header is used when trying to resolve the bitrate.

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Postby cartwright.d » Fri Jul 14, 2006 6:16 pm

I can't wait for VBR transcoding!! This will save tremendous amounts of precious bandwidth at my client sites.
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