章 7. 多媒體

This section is for users who prefer to statically compile in support for the sound card in a custom kernel. For more information about recompiling a kernel, refer to 設定 FreeBSD 核心.

When using a custom kernel to provide sound support, make sure that the audio framework driver exists in the custom kernel configuration file:

Next, add support for the sound card. To continue the example of the built-in audio chipset based on the Intel specification from the previous section, use the following line in the custom kernel configuration file:

Be sure to read the manual page of the driver for the device name to use for the driver.

Non-PnP ISA sound cards may require the IRQ and I/O port settings of the card to be added to /boot/device.hints. During the boot process, loader(8) reads this file and passes the settings to the kernel. For example, an old Creative SoundBlaster™ 16 ISA non-PnP card will use the snd_sbc(4) driver in conjunction with snd_sb16. For this card, the following lines must be added to the kernel configuration file:

If the card uses the 0x220 I/O port and IRQ 5, these lines must also be added to /boot/device.hints:

The syntax used in /boot/device.hints is described in sound(4) and the manual page for the driver of the sound card.

The settings shown above are the defaults. In some cases, the IRQ or other settings may need to be changed to match the card. Refer to snd_sbc(4) for more information about this card.

After loading the required module or rebooting into the custom kernel, the sound card should be detected. To confirm, run dmesg | grep pcm. This example is from a system with a built-in Conexant CX20590 chipset:

The status of the sound card may also be checked using this command:

The output will vary depending upon the sound card. If no pcm devices are listed, double-check that the correct device driver was loaded or compiled into the kernel. The next section lists some common problems and their solutions.

If all goes well, the sound card should now work in FreeBSD. If the CD or DVD drive is properly connected to the sound card, one can insert an audio CD in the drive and play it with cdcontrol(1):

Various applications, such as audio/workman, provide a friendlier interface. The audio/mpg123 port can be installed to listen to MP3 audio files.

Another quick way to test the card is to send data to /dev/dsp:

where filename can be any type of file. This command should produce some noise, confirming that the sound card is working.

Connecting to a Bluetooth device is out of scope for this chapter. Refer to 藍牙 for more information.

To get Bluetooth sound sink working with FreeBSD’s sound system, users have to install audio/virtual_oss first:

audio/virtual_oss requires cuse to be loaded into the kernel:

To load cuse during system startup, run this command:

To use headphones as a sound sink with audio/virtual_oss, users need to create a virtual device after connecting to a Bluetooth audio device:

請參考 virtual_oss(8) 取得更多資訊。

常見錯誤訊息 lists some common error messages and their solutions:

Modern graphics cards often come with their own sound driver for use with HDMI. This sound device is sometimes enumerated before the sound card meaning that the sound card will not be used as the default playback device. To check if this is the case, run dmesg and look for pcm. The output looks something like this:

In this example, the graphics card (NVidia) has been enumerated before the sound card (Realtek ALC889). To use the sound card as the default playback device, change hw.snd.default_unit to the unit that should be used for playback:

where n is the number of the sound device to use. In this example, it should be 4. Make this change permanent by adding the following line to /etc/sysctl.conf:

It is often desirable to have multiple sources of sound that are able to play simultaneously. FreeBSD uses "Virtual Sound Channels" to multiplex the sound card’s playback by mixing sound in the kernel.

Three sysctl(8) knobs are available for configuring virtual channels:

This example allocates four virtual channels, which is a practical number for everyday use. Both dev.pcm.0.play.vchans=4 and dev.pcm.0.rec.vchans=4 are configurable after a device has been attached and represent the number of virtual channels pcm0 has for playback and recording. Since the pcm module can be loaded independently of the hardware drivers, hw.snd.maxautovchans indicates how many virtual channels will be given to an audio device when it is attached. Refer to pcm(4) for more information.

The correct pcm device will automatically be allocated transparently to a program that requests /dev/dsp0.

The default values for the different mixer channels are hardcoded in the source code of the pcm(4) driver. While sound card mixer levels can be changed using mixer(8) or third-party applications and daemons, this is not a permanent solution. To instead set default mixer values at the driver level, define the appropriate values in /boot/device.hints, as seen in this example:

This will set the volume channel to a default value of 50 when the pcm(4) module is loaded.

A popular graphical MP3 player is Audacious. It supports Winamp skins and additional plugins. The interface is intuitive, with a playlist, graphic equalizer, and more. Those familiar with Winamp will find Audacious simple to use. On FreeBSD, Audacious can be installed from the multimedia/audacious port or package. Audacious is a descendant of XMMS.

The audio/mpg123 package or port provides an alternative, command-line MP3 player. Once installed, specify the MP3 file to play on the command line. If the system has multiple audio devices, the sound device can also be specified:

Additional MP3 players are available in the FreeBSD Ports Collection.

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

The cdda2wav tool, which is installed with the sysutils/cdrtools suite, can be used to rip audio information from CDs.

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:

In this example, the -D 0,1,0 indicates the SCSI device 0,1,0 containing the CD to rip. Use cdrecord -scanbus to determine the correct device parameters for the system.

To rip individual tracks, use -t to specify the track:

To rip a range of tracks, such as track one to seven, specify a range:

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

Alternately, dd can be used to extract audio tracks on ATAPI drives, as described in 複製音樂 CD.

Lame is a popular MP3 encoder which can be installed from the audio/lame port. Due to patent issues, a package is not available.

The following command will convert the ripped WAV file audio01.wav to audio01.mp3:

The specified 128 kbits is a standard MP3 bitrate while the 160 and 192 bitrates provide higher quality. The higher the bitrate, the larger the size of the resulting MP3. The -h 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 in the lame manual page.

In order to burn an audio CD from MP3s, they must first be converted to a non-compressed file format. XMMS can be used to convert to the WAV format, while mpg123 can be used to convert to the raw Pulse-Code Modulation (PCM) audio data format.

To convert audio01.mp3 using mpg123, specify the name of the PCM file:

To use XMMS to convert a MP3 to WAV format, use these steps:

Both the WAV and PCM formats can be used with cdrecord. When using WAV files, there will be a small tick sound at the beginning of each track. This sound is the header of the WAV file. The audio/sox port or package can be used to remove the header:

Refer to 建立與使用 CD 媒體 for more information on using a CD burner in FreeBSD.

There are several possible ways to display video under Xorg and what works is largely hardware dependent. Each method described below will have varying quality across different hardware.

Common video interfaces include:

This section introduces some of the software available from the FreeBSD Ports Collection which can be used for video playback.

要用電視卡的話，就要載入 bktr(4) 驅動程式，這個可以透過在 /boot/loader.conf 檔加上下面這一行就可以了：

或者可以將電視卡支援靜態編譯到自訂的核心當中，若要這麼做則可在自訂核心設定檔加入以下行：

之所以要加上這些額外的驅動程式，是因為卡的各組成部分都是透過 I2C 匯流排而相互連接的。接下來，請編譯、安裝新的核心 。

要測試調諧器 (Tuner) 是否被正確的偵測，請先重新啟動系統。電視卡應該會出現在開機訊息檔中，如同此範例：

該訊息會依硬體不同而有所不同。若必要，可以使用 sysctl(8) 系統偵測的參數或者自訂核心設定選項。例如要強制使用 Philips SECAM 調諧器則可加入下列行至自訂核心設定檔：

或使用 sysctl(8)：

請參考 bktr(4) 查看 sysctl(8) 可用的參數說明及核心選項。

To use the TV card, install one of the following applications:

More applications are available in the FreeBSD Ports Collection.

If any problems are encountered with the TV card, check that the video capture chip and the tuner are supported by bktr(4) and that the right configuration options were used. For more support or to ask questions about supported TV cards, refer to the freebsd-multimedia mailing list.

MythTV uses Video for Linux (V4L) to access video input devices such as encoders and tuners. In FreeBSD, MythTV works best with USB DVB-S/C/T cards as they are well supported by the multimedia/webcamd package or port which provides a V4L userland application. Any Digital Video Broadcasting (DVB) card supported by webcamd should work with MythTV. A list of known working cards can be found at wiki.freebsd.org/WebcamCompat. Drivers are also available for Hauppauge cards in the multimedia/pvr250 and multimedia/pvrxxx ports, but they provide a non-standard driver interface that does not work with versions of MythTV greater than 0.23. Due to licensing restrictions, no packages are available and these two ports must be compiled.

The wiki.freebsd.org/HTPC page contains a list of all available DVB drivers.

要使用 Binary 套件安裝 MythTV 可：

或從 Port 套件集安裝：

Once installed, set up the MythTV database:

Then, configure the backend:

Finally, start the backend:

The GENERIC kernel includes the device drivers needed to support USB scanners. Users with a custom kernel should ensure that the following lines are present in the custom kernel configuration file:

To determine if the USB scanner is detected, plug it in and use dmesg to determine whether the scanner appears in the system message buffer. If it does, it should display a message similar to this:

In this example, an EPSON Perfection™ 1650 USB scanner was detected on /dev/ugen0.2.

If the scanner uses a SCSI interface, it is important to know which SCSI controller board it will use. Depending upon the SCSI chipset, a custom kernel configuration file may be needed. The GENERIC kernel supports the most common SCSI controllers. Refer to /usr/src/sys/conf/NOTES to determine the correct line to add to a custom kernel configuration file. In addition to the SCSI adapter driver, the following lines are needed in a custom kernel configuration file:

Verify that the device is displayed in the system message buffer:

If the scanner was not powered-on at system boot, it is still possible to manually force detection by performing a SCSI bus scan with camcontrol:

The scanner should now appear in the SCSI devices list:

Refer to scsi(4) and camcontrol(8) for more details about SCSI devices on FreeBSD.

The SANE system is split in two parts: the backends (graphics/sane-backends) and the frontends (graphics/sane-frontends or graphics/xsane). The backends provide access to the scanner. Refer to http://www.sane-project.org/sane-supported-devices.html to determine which backend supports the scanner. The frontends provide the graphical scanning interface. graphics/sane-frontends installs xscanimage while graphics/xsane installs xsane.

要由 Binary 套件安裝這兩個部份可：

或由 Port 套件集安裝

After installing the graphics/sane-backends port or package, use sane-find-scanner to check the scanner detection by the SANE system:

The output should show the interface type of the scanner and the device node used to attach the scanner to the system. The vendor and the product model may or may not appear.

Next, check if the scanner will be identified by a scanning frontend. The SANE backends include scanimage which can be used to list the devices and perform an image acquisition. Use -L to list the scanner devices. The first example is for a SCSI scanner and the second is for a USB scanner:

In this second example, 'epson2:libusb:/dev/usb:/dev/ugen0.2' is the backend name (epson2) and /dev/ugen0.2 is the device node used by the scanner.

If scanimage is unable to identify the scanner, this message will appear:

If this happens, edit the backend configuration file in /usr/local/etc/sane.d/ and define the scanner device used. For example, if the undetected scanner model is an EPSON Perfection™ 1650 and it uses the epson2 backend, edit /usr/local/etc/sane.d/epson2.conf. When editing, add a line specifying the interface and the device node used. In this case, add the following line:

Save the edits and verify that the scanner is identified with the right backend name and the device node:

Once scanimage -L sees the scanner, the configuration is complete and the scanner is now ready to use.

While scanimage can be used to perform an image acquisition from the command line, it is often preferable to use a graphical interface to perform image scanning. The graphics/sane-frontends package or port installs a simple but efficient graphical interface, xscanimage.

Alternately, xsane, which is installed with the graphics/xsane package or port, is another popular graphical scanning frontend. It offers advanced features such as various scanning modes, color correction, and batch scans. Both of these applications are usable as a GIMP plugin.

In order to have access to the scanner, a user needs read and write permissions to the device node used by the scanner. In the previous example, the USB scanner uses the device node /dev/ugen0.2 which is really a symlink to the real device node /dev/usb/0.2.0. The symlink and the device node are owned, respectively, by the wheel and operator groups. While adding the user to these groups will allow access to the scanner, it is considered insecure to add a user to wheel. A better solution is to create a group and make the scanner device accessible to members of this group.

This example creates a group called usb:

Then, make the /dev/ugen0.2 symlink and the /dev/usb/0.2.0 device node accessible to the usb group with write permissions of 0660 or 0664 by adding the following lines to /etc/devfs.rules:

Finally, add the users to usb in order to allow access to the scanner:

For more details refer to pw(8).