[SOLVED] is m4a THAT much better than flac

Frabato · 2012-04-08 04:51:23

Hi All,

I just picked up 186.5 mb worth of music in .m4a format and I thought I'd convert it to flac. When I did, it turned out to be over 500 mb and I thought, this is silly, so I converted it to wave and it turned out to be 1 gigabyte. Now, these conversions were done using dbpoweramp under wine. But my question is this, can .m4a really compress wave files to less than 1/5th of their size? I got flac to compress the wave files to about 1/2 of their original size, a bit over 500 mb. Does anyone know about this stuff that can help me understand what's going on here?

Thanks

Last edited by Frabato (2012-04-09 22:58:49)

Grinch · 2012-04-08 05:03:55

Seems to me that the m4a files in question is using lossy compression (aac?), afaik m4a can contain both lossless and lossy audio. Flac as the name implies is lossless.

/dev/zero · 2012-04-08 05:59:40

If I understand correctly, m4a is a container, whereas flac is a codec. This would imply that you could, theoretically, actually create files that are both flac and m4a, in much the same way as you can put xvid encoded video inside an avi file.

(This is actually covered on wikipedia, but okay, I won't worry about telling you to stfw this time, since I agree this stuff can seem a bit abstract.)

karol · 2012-04-08 08:23:36

Frabato wrote:

But my question is this, can .m4a really compress wave files to less than 1/5th of their size? I got flac to compress the wave files to about 1/2 of their original size, a bit over 500 mb

Flac usually compresses to about half the size but it does so w/o any loss of quality.
You can easily compress to 1/11th of the original wav file by coding it down to 128kbps mp3s. Need more compression - pick libvorbis-aotuv [1] and see if tiny (about 64kbps) ogg files still sound decent to you.

graysky · 2012-04-08 10:51:48

/dev/zero wrote:

If I understand correctly, m4a is a container, whereas flac is a codec. This would imply that you could, theoretically, actually create files that are both flac and m4a, in much the same way as you can put xvid encoded video inside an avi file.

**ding ding ding**

Correct answer

Perhaps a package like mediainfo can tell you the codec used to compress the stream inside your m4a files.

/dev/zero · 2012-04-08 11:54:57

Check it:

I first convert a wav file into m4a,

ffmpeg -i /usr/share/sounds/alsa/Side_Right.wav -y -strict experimental -acodec aac -ar 48000 -ab 256k ./Side_Right.m4a

Now let's have a peak under its hood.

$ ffprobe ./Side_Right.m4a 
ffprobe version 0.10.2 Copyright (c) 2007-2012 the FFmpeg developers
  built on Mar 19 2012 11:26:39 with gcc 4.6.3
  configuration: --prefix=/usr --enable-libmp3lame --enable-libvorbis --enable-libxvid --enable-libx264 --enable-libvpx --enable-libvo-aacenc --enable-libtheora --enable-libgsm --enable-libspeex --enable-postproc --enable-shared --enable-x11grab --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libschroedinger --enable-libopenjpeg --enable-librtmp --enable-libpulse --enable-gpl --enable-version3 --enable-runtime-cpudetect --disable-debug --disable-static
  libavutil      51. 35.100 / 51. 35.100
  libavcodec     53. 61.100 / 53. 61.100
  libavformat    53. 32.100 / 53. 32.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 61.100 /  2. 61.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from './Side_Right.m4a':
  Metadata:
    major_brand     : M4A 
    minor_version   : 512
    compatible_brands: isomiso2
    encoder         : Lavf53.32.100
  Duration: 00:00:01.36, start: 0.000000, bitrate: 218 kb/s
    Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, mono, s16, 212 kb/s
    Metadata:
      handler_name    :

You can clearly see from the output of ffprobe that I've encoded the audio as aac. Less obviously, the container is mp4/m4a; this is apparent not just from the file extension (which I wouldn't necessarily trust), but also the major_brand field. The moral of the story is, the container (-> file extension) doesn't really have much to do with what kind of compression is taking place.

It's like if you move house, it doesn't really matter whether the removalists drive an Isuzu or a Mitsubishi, all you care about is the trade-off between them not charging you much money and them not breaking all your gear (lossy vs lossless). Of course, the kind of truck does matter if you have a strange environment such as a steep driveway or restrictive road rules (and likewise, not all containers are universally well-recognised by all devices - ogg quickly comes to mind).

Last edited by /dev/zero (2012-04-08 11:58:01)

R00KIE · 2012-04-08 13:58:51

/dev/zero wrote:

If I understand correctly, m4a is a container, whereas flac is a codec.

According to wikipedia[1] flac can also be the name of the container for flac encoded files.

A simple container format for the stream, also called FLAC (or Native FLAC)

[1] http://en.wikipedia.org/wiki/FLAC#Composition

.:B:. · 2012-04-08 14:42:51

M4a can only be a container afaik, mostly for AAC; FLAC can be both a container and a codec. So you're comparing apples and oranges.

Unless your m4a files are lossless (and at this size, it is very improbable), there is no reason to convert to FLAC. Quality will not improve; only deteriorate.

Last edited by .:B:. (2012-04-08 14:43:48)

Frabato · 2012-04-09 15:45:33

Thanks to all for the piles of replies. One reason for my confusion is that I thought m4a was always lossless. I've converted .m4a to flac many times and the flac files were always just slightly larger than the original .m4a's so when I saw the size difference here I was indeed perplexed. I ran ffprobe on one of the files but I'm not sure how to tell the level of compression. If it is compressed then I suppose I'm better off leaving it as an .m4a.
Here is the output:

ffprobe version 0.10.2 Copyright (c) 2007-2012 the FFmpeg developers
built on Mar 21 2012 07:09:54 with gcc 4.6.3
configuration: --prefix=/usr --extra-cflags='-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Wformat-security -Werror=format-security ' --extra-ldflags='-Wl,-z,relro' --cc='ccache cc' --enable-shared --enable-libmp3lame --enable-gpl --enable-nonfree --enable-libdirac --disable-decoder=libdirac --enable-libvorbis --enable-pthreads --enable-libfaac --enable-libxvid --enable-postproc --enable-x11grab --enable-libgsm --enable-libtheora --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libx264 --enable-libspeex --enable-nonfree --disable-stripping --enable-libschroedinger --disable-encoder=libschroedinger --enable-version3 --enable-libopenjpeg --enable-libvpx --enable-librtmp --enable-avfilter --enable-libfreetype --enable-libvo-aacenc --disable-decoder=amrnb --enable-libvo-amrwbenc --enable-libaacplus --libdir=/usr/lib/x86_64-linux-gnu --disable-vda --enable-libdc1394 --disable-altivec --disable-armv5te --disable-armv6 --disable-vis --shlibdir=/usr/lib/x86_64-linux-gnu
libavutil 51. 35.100 / 51. 35.100
libavcodec 53. 61.100 / 53. 61.100
libavformat 53. 32.100 / 53. 32.100
libavdevice 53. 4.100 / 53. 4.100
libavfilter 2. 61.100 / 2. 61.100
libswscale 2. 1.100 / 2. 1.100
libswresample 0. 6.100 / 0. 6.100
libpostproc 52. 0.100 / 52. 0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'test.m4a':
Metadata:
major_brand : M4A
minor_version : 0
compatible_brands: M4A mp42isom
creation_time : 2010-06-06 12:14:17
title :
artist :
composer :
album :
track : 1/21
disc : 1/2
date : 1966
gapless_playback: 0
encoder : iTunes 9.1.1.12, QuickTime 7.6.6
genre : Pop/Rock
Duration: 00:02:21.15, start: 0.000000, bitrate: 296 kb/s
Stream #0:0(und): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, s16, 287 kb/s
Metadata:
creation_time : 2010-06-06 12:14:17
handler_name :

Should I leave the file as is. Does anyone know how to interpret this stuff?

Thanks

.:B:. · 2012-04-09 16:24:18

The bitrate is often the most reliable indicator. FLAC often hits 1 Mbps; heavier MP3 encodes do ~300 Kbps.

Frabato · 2012-04-09 17:11:04

OK, so the best thing is to leave these files as .m4a's. Thanks to everyone for your help!

DSpider · 2012-04-09 17:39:21

Exactly. Trying to convert a lossy format to lossless is redundant. You're not improving the quality.

PS: Here's what I wanted to say before I scrolled down and saw your reply (thought I should post it anyway since I bothered to write it):

".m4a" is just an mp4 container to indicate audio, just like ".m4v" is an mp4 container to indicate video. In fact, you can even change the extension from a (DRM-free) .m4a (or .m4v) file to .mp4 and it will work fine:

http://en.wikipedia.org/wiki/M4a#.MP4_versus_.M4A
http://en.wikipedia.org/wiki/M4v

As you can see, Apple stuck their nasty, slimy little tail into it (just like they did with ePub, but that's a different story).

FLAC's description here: http://flac.sourceforge.net/index.html. Maybe check out the FAQ.

Arch Linux

#1 2012-04-08 04:51:23

[SOLVED] is m4a THAT much better than flac

#2 2012-04-08 05:03:55

Re: [SOLVED] is m4a THAT much better than flac

#3 2012-04-08 05:59:40

Re: [SOLVED] is m4a THAT much better than flac

#4 2012-04-08 08:23:36

Re: [SOLVED] is m4a THAT much better than flac

#5 2012-04-08 10:51:48

Re: [SOLVED] is m4a THAT much better than flac

#6 2012-04-08 11:54:57

Re: [SOLVED] is m4a THAT much better than flac

#7 2012-04-08 13:58:51

Re: [SOLVED] is m4a THAT much better than flac

#8 2012-04-08 14:42:51

Re: [SOLVED] is m4a THAT much better than flac

#9 2012-04-09 15:45:33

Re: [SOLVED] is m4a THAT much better than flac

#10 2012-04-09 16:24:18

Re: [SOLVED] is m4a THAT much better than flac

#11 2012-04-09 17:11:04

Re: [SOLVED] is m4a THAT much better than flac

#12 2012-04-09 17:39:21

Re: [SOLVED] is m4a THAT much better than flac

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