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Getting ready to transcode library to AAC
Eli
post Jan 18 2013, 14:59
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I am getting ready to transcode my ~2TB flac library to AAC-LC in an MP4 container and want to be sure I get it right.

My intention is to encode at ~96kbps TVBR with QAAC. The goal is for portability and streaming, and this seems to be a good quality level that will give reasonable listening (I still have the lossless archive).

Is TVBR widely supported? I know many years ago when I used to encode to LAME MP3 VBR ipods had a hard time with it.



I need to pick the right tool for transcoding and have some specific tasks that I want to achieve and can hopefully achieve all of them in one transcode step.

- Scale down album art automatically. Probably to <50kb and 500x500. Is this still to big?
--- 90+% of my albums have embedded and folder.jpg, a minority have one or the other. If they differ, I would like to scale down from the higher resolution one.

- Identify HDCD tracks, and encode to 24b on the fly

- Identify pre-emph files and de-emph

- Apply EBU R128 ReplayGain ( I still need to calculate EBU R128 ReplayGain values for my flac files)

Is there a tool that can do all of these?

This post has been edited by Eli: Jan 18 2013, 15:18


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Dynamic
post Jan 19 2013, 14:04
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To the OP,

Foobar2000, CUETools and dBpowerAmp all cover a lot of the aspects you require and copy over your tags happily.

The first part - about your AAC encoder choice and settings is answered above. I don't believe CUETools lets you use a commandline encoder, so might not be the choice here. I've often been pleasantly surprised that speech, mono and near-mono files and some vintage material often come out at greatly reduced bitrates using VBR (so TVBR might come into its own in such instances)

HDCD: I think CUETools will detect HDCD if you set that option, and foobar2000 will also detect it using foo_hdcd.

Foobar2000 can have the foo_hdcd encoder in the DSP chain of the Convert... function (separate from the playback DSP chain) and decode on the fly using its floating point high bit-depth pipeline to maintain maximum quality.

CUETools could pre-process any such albums to 20-bit in a 24-bit container, but I don't think it lets you access QAAC (only neroaacenc). It might be worth using CueTools to verify your lossless rips for accuracy anyway.

Might want to test them with one or two of your actual HDCD albums to ensure they apply it to all tracks on the same CD, because HDCD specifies a -6 dB volume adjustment to allow room for peak extension, so you might end up with inconsistent volume through the album.

Alternatively, give up on HDCD detection, as they sound pretty damned good undecoded. I should get round to ABXing the few I have at matched volume one day to see if it's worth it for me.

Pre-emphasis is something I've not experienced, but there are threads about it and lists of pre-emphasised releases, which you can look up to see if anything you own is among them, allowing you to test for detection. Definitely desirable to de-emphasise any such CDs.

Album Art: I've seen options regarding album art size in some tools I use (probably fb2k or CUETools), but haven't used them much.

There are various external tagging tools and the fb2k plugin foo_masstagger that might have options you want.

dBpowerAmp Converter is also pretty full of options developed for mass transcoding with very much the sort of requirements you have, and I think that includes tag checking against multiple sources (PerfectMeta) and album art choices too.

ReplayGain: I personally nearly always wish to play back at Album Gain volume even in non-RG-aware players (and I'm not too bothered whether it's the original or R-128 method that is used - they're much closer for Album Gain, a bit more varied with Track Gain), so I usually encode with foobar2000's Converter and choose Apply Album Gain in its ReplayGain settings before the audio is sent to the encoder. I then rescan after encoding to generate track gain (and all my Album Gain values are close to 0.00 dB). When I've ripped a load of lossless files I throw them into fb2k and scan as albums according to tags, which is very quick at scanning and tagging them with RG metadata and then ready for me to convert with gain applied. Whether you apply the gain before encoding or rely on your player all implementing RG from tags, it's still worth scanning after conversion.

I believe dBpowerAmp's DSP plugin system also lets you deal with ReplayGain when converting, though I'm unaware of whether it applies the EBU R-128 or original algorithm or gives you the option.

Overall, for my uses, I probably favour foobar2000 for this sort of task, but definitely like features of CueTools too and have found dBpowerAmp Converter's shell integration handy for speeding up some conversion tasks (e.g. FLAC to ALAC, or some quick Vorbis encodes to throw on my phone). I'd be quite happy to split the requirements among 2 or 3 programs.

Also, I'd probably make a text file in Notepad to paste in various settings for future reference (e.g. if I want to re-encode for another device, which might have, say, Opus support or a larger memory card), and after completion, I often also record the actual number of tracks encoded, duration, average bitrate etc. from the selection properties of fb2k. For example, I like to record my destination folder and file naming format, e.g.

%album artist%\%album% - %date%\%track% - %title% - %artist%

and also I record my encoder version and commandline switches (if specified as a custom encoder) and the bit-depth passed to it.

Best of luck, and please report your findings.

This post has been edited by Dynamic: Jan 19 2013, 14:12
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