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Background:

I have a music playlist of .M4A files (AAC codecs) at varying bitrates that I'd like to lower to a set bitrate for the purpose of conserving space on the phone that I'll be transferring them to. Because many of these files were downloaded directly from YouTube (using youtube-dl), I'd like to avoid re-encoding them.

Therefore, I'm looking for a Windows program that...

  • Works on Windows 7
  • Is free
  • Is a GUI program, not a command-line solution
  • Is able to convert a batch of .M4A files to a set bitrate without re-encoding

Thanks, would really appreciate any help in advance.

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    By definition if you change the bitrate you will have to re-encode - otherwise you will get nonsense - it is a bit like saying that you wish to change then number of pages in a book without re-laying out the text. – Steve Barnes Nov 12 '16 at 12:42
  • So it can't be done? Are you positive on that? I could have sworn I've heard references to lossless re-encoding during my extensive reading up on the topic, especially when it concerns the same file format. Maybe I misunderstood. – Hashim Nov 12 '16 at 23:21
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    Lossless re-encoding is not the same as without re-encoding which is what your question is asking! So yes I am 100% sure that what you are currently asking cannot be done. – Steve Barnes Nov 13 '16 at 4:05
  • Sorry, to clarify; when I said lossless re-encoding, I meant re-encoding lossy files without further loss, rather than re-encoding lossless file formats. – Hashim Nov 14 '16 at 2:02
  • The problem is that your question says "without re-encoding" not "re-encoding without further loss" - Anyway a lower bit rate will almost always result in further losses as there is less data bandwidth available in a lower bit rate - that is what it means. – Steve Barnes Nov 14 '16 at 6:18
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+50

Frankly the question as asked cannot be done as changing the bit rate must always require re-encoding and reducing the bit rate will almost always reduce the quality of the track - the exceptions will be when the track had already been processed to increase the bit rate above that which was originally recorded but not always in this case or for simple waveforms that fit the new bit rate as well as they do the old.

Think of it as changing the size of the pages in a book, unless you reflow or scale the text and images you cannot do it and retain all of the original information unless you are lucky enough that all of the page contents fit within the new page dimensions without change because there happened to be large borders.

There are a number of GUI based Audio Editors that can change the bit rate on save or export and support .M4A format, necessarily re-encoding the format but not many that I know of that support batch processing.

  • Audacity allows you to create a 'Chain' of operations which can include exporting with given settings and apply them to the opened file but opens a window for each file so still requires a fair amount of manual intervention.
  • VLC Media Player may well be able to do this but it certainly isn't clear how.

This brings us back to a not GUI option FFMPEG which can do this with ease and with minimal loss of quality. This can easily be input into a batch file containing something like:

REM UNTESTED!
for fn in $* (
   ffmpeg -i %fn% -c:a aac -b:a 160k fixedrate/%fn%
)

That you coud then drop your files onto.

There are a number of FFMPEG GUIs such as AVAINTI & FfmpegYAG that are worth checking out.

  • Thanks, Steve. With regards to the ffmpeg syntax - don't percent signs have to be doubled up for batch files? – Hashim Nov 17 '16 at 22:46
  • @Hashim as I said untested – Steve Barnes Nov 18 '16 at 6:29
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Hashim, Have you looked into what VLC can do: https://www.vlchelp.com/convert-audio-format/ ?

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