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norderney
2010-10-28, 15:41
Just curious about MPEG-4 which is the file format used by iTunes.

I noticed that the bit rate on downloaded tracks shows as 256kbps CBR, but it then says Converted to 705kbps FLAC.

How does this actually work? I know with MP3 files you CANNOT convert an MP3 file to FLAC, so how is MPEG-4 able to convert the 256kps file to 705kps FLAC?

Are MPEG-4 files of higher quality than MP3 files?

JJZolx
2010-10-28, 16:07
Just curious about MPEG-4 which is the file format used by iTunes.

I noticed that the bit rate on downloaded tracks shows as 256kbps CBR, but it then says Converted to 705kbps FLAC.

How does this actually work? I know with MP3 files you CANNOT convert an MP3 file to FLAC, so how is MPEG-4 able to convert the 256kps file to 705kps FLAC?

Are MPEG-4 files of higher quality than MP3 files?

AAC (.mp4 files) can't be decoded natively on older Squeezeboxes (Touch and Radio can do it), so Squeezebox Server decodes them to WAV and then encodes that into FLAC for streaming. The reason for the FLAC encoding is to save bandwidth.

There's only one lossy decoding being done, and then a lossless encoding, so there's no loss in quality in the process.

Technically, you can transcode from just about any format to any other. What you're thinking of is the general advice that once you've encoded something in a lossy codec like MP3 or AAC that the quality is lost forever. You lose additional quality if you transcode the file to another lossless (or even the same) codec.

Skinny
2010-10-28, 22:34
What you're thinking of is the general advice that once you've encoded something in a lossless codec like MP3 or AAC that the quality is lost forever.

I'm sure you mean lossy, then this is absolutely true.

@ OP yes, AAC is a more advanced audio format than MP3 and is supposed to give better quality at the same bitrate. My understanding is that the difference is greater the lower the bitrate.

-Skinny

bigblackdog
2010-10-29, 02:06
Would I be correct in thinking that the touch therefore is a better option than the duet when streaming the apple lossless files. I have approximate 66,000 songs all in apple lossless and it seems that my system is 'slowing down'. Considering switching from the duet just for 24/96.
Would seem to me that if the server has to do less work then should free it upmarket bit

Skinny
2010-10-31, 04:15
(...) I have approximate 66,000 songs all in apple lossless and it seems that my system is 'slowing down'. (...)
Would seem to me that if the server has to do less work then should free it upmarket bit

By default, when you play a format not supported by a player (such as Apple Lossless Audio Compression on the SBR), it is converted to FLAC for streaming to the player. You can disable FLAC compression if you wish to ease the CPU load a little. The audio is then streamed as uncompressed PCM to the player. The only difference is a small increase in your local network traffic. Sound quality is unaffected.

In the Web UI, go to Server Settings --> Advanced --> File Types. For Apple Lossless, choose FLAC [Disabled] and make sure PCM is enabled [faad]. Click Apply.

You may need to restart the server.

-Skinny