7.3. MP3 音樂

Contributed by Chern Lee.

MP3 (MPEG Layer 3 Audio) accomplishes near CD-quality sound, leaving no reason to let your FreeBSD workstation fall short of its offerings.

7.3.1. MP3 Players

By far, the most popular X11 MP3 player is XMMS (X Multimedia System). Winamp skins can be used with XMMS since the GUI is almost identical to that of Nullsoft's Winamp. XMMS also has native plug-in support.

XMMS can be installed from the multimedia/xmms port or package.

XMMS' interface is intuitive, with a playlist, graphic equalizer, and more. Those familiar with Winamp will find XMMS simple to use.

The audio/mpg123 port is an alternative, command-line MP3 player.

mpg123 can be run by specifying the sound device and the MP3 file on the command line, as shown below:

# mpg123 -a /dev/dsp1.0 Foobar-GreatestHits.mp3
High Performance MPEG 1.0/2.0/2.5 Audio Player for Layer 1, 2 and 3.
Version 0.59r (1999/Jun/15). Written and copyrights by Michael Hipp.
Uses code from various people. See 'README' for more!
THIS SOFTWARE COMES WITH ABSOLUTELY NO WARRANTY! USE AT YOUR OWN RISK!





Playing MPEG stream from Foobar-GreatestHits.mp3 ...
MPEG 1.0 layer III, 128 kbit/s, 44100 Hz joint-stereo

/dev/dsp1.0 should be replaced with the dsp device entry on your system.

7.3.2. Ripping CD Audio Tracks

Before encoding a CD or CD track to MP3, the audio data on the CD must be ripped onto the hard drive. This is done by copying the raw CDDA (CD Digital Audio) data to WAV files.

The cdda2wav tool, which is a part of the sysutils/cdrtools suite, is used for ripping audio information from CDs and the information associated with them.

With the audio CD in the drive, the following command can be issued (as root) to rip an entire CD into individual (per track) WAV files:

# cdda2wav -D 0,1,0 -B

cdda2wav will support ATAPI (IDE) CDROM drives. To rip from an IDE drive, specify the device name in place of the SCSI unit numbers. For example, to rip track 7 from an IDE drive:

# cdda2wav -D /dev/acd0a -t 7

The -D 0,1,0 indicates the SCSI device 0,1,0, which corresponds to the output of cdrecord -scanbus.

To rip individual tracks, make use of the -t option as shown:

# cdda2wav -D 0,1,0 -t 7

This example rips track seven of the audio CDROM. To rip a range of tracks, for example, track one to seven, specify a range:

# cdda2wav -D 0,1,0 -t 1+7

The utility dd(1) can also be used to extract audio tracks on ATAPI drives, read 節 18.6.5, “Duplicating Audio CDs” for more information on that possibility.

7.3.3. Encoding MP3s

Nowadays, the mp3 encoder of choice is lame. Lame can be found at audio/lame in the ports tree.

Using the ripped WAV files, the following command will convert audio01.wav to audio01.mp3:

# lame -h -b 128 \
--tt "Foo Song Title" \
--ta "FooBar Artist" \
--tl "FooBar Album" \
--ty "2001" \
--tc "Ripped and encoded by Foo" \
--tg "Genre" \
audio01.wav audio01.mp3

128 kbits seems to be the standard MP3 bitrate in use. Many enjoy the higher quality 160, or 192. The higher the bitrate, the more disk space the resulting MP3 will consume--but the quality will be higher. The -h option turns on the higher quality but a little slower mode. The options beginning with --t indicate ID3 tags, which usually contain song information, to be embedded within the MP3 file. Additional encoding options can be found by consulting the lame man page.

7.3.4. Decoding MP3s

In order to burn an audio CD from MP3s, they must be converted to a non-compressed WAV format. Both XMMS and mpg123 support the output of MP3 to an uncompressed file format.

Writing to Disk in XMMS:

  1. Launch XMMS.

  2. Right-click on the window to bring up the XMMS menu.

  3. Select Preference under Options.

  4. Change the Output Plugin to Disk Writer Plugin.

  5. Press Configure.

  6. Enter (or choose browse) a directory to write the uncompressed files to.

  7. Load the MP3 file into XMMS as usual, with volume at 100% and EQ settings turned off.

  8. Press Play —— XMMS will appear as if it is playing the MP3, but no music will be heard. It is actually playing the MP3 to a file.

  9. Be sure to set the default Output Plugin back to what it was before in order to listen to MP3s again.

Writing to stdout in mpg123:

  • Run mpg123 -s audio01.mp3 > audio01.pcm

XMMS writes a file in the WAV format, while mpg123 converts the MP3 into raw PCM audio data. Both of these formats can be used with cdrecord to create audio CDs. You have to use raw PCM with burncd(8). If you use WAV files, you will notice a small tick sound at the beginning of each track, this sound is the header of the WAV file. You can simply remove the header of a WAV file with the utility SoX (it can be installed from the audio/sox port or package):

% sox -t wav -r 44100 -s -w -c 2 track.wav track.raw

Read 節 18.6, “Creating and Using Optical Media (CDs)” for more information on using a CD burner in FreeBSD.

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