7.4. 播放影片
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## 7.4. 播放影片

Contributed by Ross Lippert.

Video playback is a very new and rapidly developing application area. Be patient. Not everything is going to work as smoothly as it did with sound.

Before you begin, you should know the model of the video card you have and the chip it uses. While Xorg and XFree86™ support a wide variety of video cards, fewer give good playback performance. To obtain a list of extensions supported by the X server using your card use the command xdpyinfo(1) while X11 is running.

It is a good idea to have a short MPEG file which can be treated as a test file for evaluating various players and options. Since some DVD players will look for DVD media in `/dev/dvd` by default, or have this device name hardcoded in them, you might find it useful to make symbolic links to the proper devices:

`#` `ln -sf /dev/acd0c /dev/dvd` `#` `ln -sf /dev/racd0c /dev/rdvd`

On FreeBSD 5.X, which uses devfs(5) there is a slightly different set of recommended links:

`#` `ln -sf /dev/acd0 /dev/dvd` `#` `ln -sf /dev/acd0 /dev/rdvd`

Note that due to the nature of devfs(5), manually created links like these will not persist if you reboot your system. In order to create the symbolic links automatically whenever you boot your system, add the following lines to `/etc/devfs.conf`:

link acd0 dvd link acd0 rdvd

Additionally, DVD decryption, which requires invoking special DVD-ROM functions, requires write permission on the DVD devices.

Some of the ports discussed rely on the following kernel options to build correctly. Before attempting to build, add this option to the kernel configuration file, build a new kernel, and reboot:

options CPU_ENABLE_SSE

### 注意:

On FreeBSD 4.X `options USER_LDT` should be added to the kernel configuration file. This option is not available on FreeBSD 5.X and later version.

To enhance the shared memory X11 interface, it is recommended that the values of some sysctl(8) variables should be increased:

kern.ipc.shmmax=67108864 kern.ipc.shmall=32768

### 7.4.1. Determining Video Capabilities

There are several possible ways to display video under X11. What will really work is largely hardware dependent. Each method described below will have varying quality across different hardware. Secondly, the rendering of video in X11 is a topic receiving a lot of attention lately, and with each version of Xorg, or of XFree86™, there may be significant improvement.

A list of common video interfaces:

1. X11: normal X11 output using shared memory.

2. XVideo: an extension to the X11 interface which supports video in any X11 drawable.

3. SDL: the Simple Directmedia Layer.

4. DGA: the Direct Graphics Access.

5. SVGAlib: low level console graphics layer.

#### 7.4.1.1. XVideo

Xorg and XFree86™ 4.X have an extension called XVideo (aka Xvideo, aka Xv, aka xv) which allows video to be directly displayed in drawable objects through a special acceleration. This extension provides very good quality playback even on low-end machines.

To check whether the extension is running, use `xvinfo`:

`%` `xvinfo`

XVideo is supported for your card if the result looks like:

X-Video Extension version 2.2 screen #0 Adaptor #0: "Savage Streams Engine" number of ports: 1 port base: 43 operations supported: PutImage supported visuals: depth 16, visualID 0x22 depth 16, visualID 0x23 number of attributes: 5 "XV_COLORKEY" (range 0 to 16777215) client settable attribute client gettable attribute (current value is 2110) "XV_BRIGHTNESS" (range -128 to 127) client settable attribute client gettable attribute (current value is 0) "XV_CONTRAST" (range 0 to 255) client settable attribute client gettable attribute (current value is 128) "XV_SATURATION" (range 0 to 255) client settable attribute client gettable attribute (current value is 128) "XV_HUE" (range -180 to 180) client settable attribute client gettable attribute (current value is 0) maximum XvImage size: 1024 x 1024 Number of image formats: 7 id: 0x32595559 (YUY2) guid: 59555932-0000-0010-8000-00aa00389b71 bits per pixel: 16 number of planes: 1 type: YUV (packed) id: 0x32315659 (YV12) guid: 59563132-0000-0010-8000-00aa00389b71 bits per pixel: 12 number of planes: 3 type: YUV (planar) id: 0x30323449 (I420) guid: 49343230-0000-0010-8000-00aa00389b71 bits per pixel: 12 number of planes: 3 type: YUV (planar) id: 0x36315652 (RV16) guid: 52563135-0000-0000-0000-000000000000 bits per pixel: 16 number of planes: 1 type: RGB (packed) depth: 0 red, green, blue masks: 0x1f, 0x3e0, 0x7c00 id: 0x35315652 (RV15) guid: 52563136-0000-0000-0000-000000000000 bits per pixel: 16 number of planes: 1 type: RGB (packed) depth: 0 red, green, blue masks: 0x1f, 0x7e0, 0xf800 id: 0x31313259 (Y211) guid: 59323131-0000-0010-8000-00aa00389b71 bits per pixel: 6 number of planes: 3 type: YUV (packed) id: 0x0 guid: 00000000-0000-0000-0000-000000000000 bits per pixel: 0 number of planes: 0 type: RGB (packed) depth: 1 red, green, blue masks: 0x0, 0x0, 0x0

Also note that the formats listed (YUV2, YUV12, etc) are not present with every implementation of XVideo and their absence may hinder some players.

If the result looks like:

X-Video Extension version 2.2 screen #0 no adaptors present

Then XVideo is probably not supported for your card.

If XVideo is not supported for your card, this only means that it will be more difficult for your display to meet the computational demands of rendering video. Depending on your video card and processor, though, you might still be able to have a satisfying experience. You should probably read about ways of improving performance in the advanced reading 節 7.4.3, “Further Reading”.

#### 7.4.1.2. Simple Directmedia Layer

The Simple Directmedia Layer, SDL, was intended to be a porting layer between Microsoft® Windows®, BeOS, and UNIX®, allowing cross-platform applications to be developed which made efficient use of sound and graphics. The SDL layer provides a low-level abstraction to the hardware which can sometimes be more efficient than the X11 interface.

The SDL can be found at `devel/sdl12`.

#### 7.4.1.3. Direct Graphics Access

Direct Graphics Access is an X11 extension which allows a program to bypass the X server and directly alter the framebuffer. Because it relies on a low level memory mapping to effect this sharing, programs using it must be run as `root`.

The DGA extension can be tested and benchmarked by dga(1). When `dga` is running, it changes the colors of the display whenever a key is pressed. To quit, use q.

### 7.4.2. Ports and Packages Dealing with Video

This section discusses the software available from the FreeBSD Ports Collection which can be used for video playback. Video playback is a very active area of software development, and the capabilities of various applications are bound to diverge somewhat from the descriptions given here.

Firstly, it is important to know that many of the video applications which run on FreeBSD were developed as Linux applications. Many of these applications are still beta-quality. Some of the problems that you may encounter with video packages on FreeBSD include:

1. An application cannot playback a file which another application produced.

2. An application cannot playback a file which the application itself produced.

3. The same application on two different machines, rebuilt on each machine for that machine, plays back the same file differently.

4. A seemingly trivial filter like rescaling of the image size results in very bad artifacts from a buggy rescaling routine.

5. An application frequently dumps core.

6. Documentation is not installed with the port and can be found either on the web or under the port's `work` directory.

Many of these applications may also exhibit “Linux-isms”. That is, there may be issues resulting from the way some standard libraries are implemented in the Linux distributions, or some features of the Linux kernel which have been assumed by the authors of the applications. These issues are not always noticed and worked around by the port maintainers, which can lead to problems like these:

1. The use of `/proc/cpuinfo` to detect processor characteristics.

2. A misuse of threads which causes a program to hang upon completion instead of truly terminating.

3. Software not yet in the FreeBSD Ports Collection which is commonly used in conjunction with the application.

So far, these application developers have been cooperative with port maintainers to minimize the work-arounds needed for port-ing.

#### 7.4.2.1. MPlayer

MPlayer is a recently developed and rapidly developing video player. The goals of the MPlayer team are speed and flexibility on Linux and other Unices. The project was started when the team founder got fed up with bad playback performance on then available players. Some would say that the graphical interface has been sacrificed for a streamlined design. However, once you get used to the command line options and the key-stroke controls, it works very well.

##### 7.4.2.1.1. Building MPlayer

MPlayer resides in `multimedia/mplayer`. MPlayer performs a variety of hardware checks during the build process, resulting in a binary which will not be portable from one system to another. Therefore, it is important to build it from ports and not to use a binary package. Additionally, a number of options can be specified in the `make` command line, as described in the `Makefile` and at the start of the build:

`#` `cd /usr/ports/multimedia/mplayer` `#` `make` N - O - T - E Take a careful look into the Makefile in order to learn how to tune mplayer towards you personal preferences! For example, make WITH_GTK1 builds MPlayer with GTK1-GUI support. If you want to use the GUI, you can either install /usr/ports/multimedia/mplayer-skins or download official skin collections from http://www.mplayerhq.hu/homepage/dload.html

The default port options should be sufficient for most users. However, if you need the XviD codec, you have to specify the `WITH_XVID` option in the command line. The default DVD device can also be defined with the `WITH_DVD_DEVICE` option, by default `/dev/acd0` will be used.

As of this writing, the MPlayer port will build its HTML documentation and two executables, `mplayer`, and `mencoder`, which is a tool for re-encoding video.

The HTML documentation for MPlayer is very informative. If the reader finds the information on video hardware and interfaces in this chapter lacking, the MPlayer documentation is a very thorough supplement. You should definitely take the time to read the MPlayer documentation if you are looking for information about video support in UNIX®.

##### 7.4.2.1.2. Using MPlayer

Any user of MPlayer must set up a `.mplayer` subdirectory of her home directory. To create this necessary subdirectory, you can type the following:

`%` `cd /usr/ports/multimedia/mplayer` `%` `make install-user`

The command options for `mplayer` are listed in the manual page. For even more detail there is HTML documentation. In this section, we will describe only a few common uses.

To play a file, such as ``testfile.avi``, through one of the various video interfaces set the `-vo` option:

`%` `mplayer -vo xv testfile.avi`
`%` `mplayer -vo sdl testfile.avi`
`%` `mplayer -vo x11 testfile.avi`
`#` `mplayer -vo dga testfile.avi`
`#` `mplayer -vo 'sdl:dga' testfile.avi`

It is worth trying all of these options, as their relative performance depends on many factors and will vary significantly with hardware.

To play from a DVD, replace the `testfile.avi` with `dvd://`N` -dvd-device `DEVICE`` where `N` is the title number to play and ``DEVICE`` is the device node for the DVD-ROM. For example, to play title 3 from `/dev/dvd`:

`#` `mplayer -vo xv dvd://3 -dvd-device /dev/dvd`

### 注意:

The default DVD device can be defined during the build of the MPlayer port via the `WITH_DVD_DEVICE` option. By default, this device is `/dev/acd0`. More details can be found in the port `Makefile`.

To stop, pause, advance and so on, consult the keybindings, which are output by running `mplayer -h` or read the manual page.

Additional important options for playback are: `-fs -zoom` which engages the fullscreen mode and `-framedrop` which helps performance.

In order for the mplayer command line to not become too large, the user can create a file `.mplayer/config` and set default options there:

vo=xv fs=yes zoom=yes

Finally, `mplayer` can be used to rip a DVD title into a `.vob` file. To dump out the second title from a DVD, type this:

`#` `mplayer -dumpstream -dumpfile out.vob dvd://2 -dvd-device /dev/dvd`

The output file, `out.vob`, will be MPEG and can be manipulated by the other packages described in this section.

##### 7.4.2.1.3. mencoder

Before using `mencoder` it is a good idea to familiarize yourself with the options from the HTML documentation. There is a manual page, but it is not very useful without the HTML documentation. There are innumerable ways to improve quality, lower bitrate, and change formats, and some of these tricks may make the difference between good or bad performance. Here are a couple of examples to get you going. First a simple copy:

`%` `mencoder input.avi -oac copy -ovc copy -o output.avi`

Improper combinations of command line options can yield output files that are unplayable even by `mplayer`. Thus, if you just want to rip to a file, stick to the `-dumpfile` in `mplayer`.

To convert `input.avi` to the MPEG4 codec with MPEG3 audio encoding (`audio/lame` is required):

`%` `mencoder input.avi -oac mp3lame -lameopts br=192 \ -ovc lavc -lavcopts vcodec=mpeg4:vhq -o output.avi`

This has produced output playable by `mplayer` and `xine`.

`input.avi` can be replaced with `dvd://1 -dvd-device /dev/dvd` and run as `root` to re-encode a DVD title directly. Since you are likely to be dissatisfied with your results the first time around, it is recommended you dump the title to a file and work on the file.

#### 7.4.2.2. The xine Video Player

The xine video player is a project of wide scope aiming not only at being an all in one video solution, but also in producing a reusable base library and a modular executable which can be extended with plugins. It comes both as a package and as a port, `multimedia/xine`.

The xine player is still very rough around the edges, but it is clearly off to a good start. In practice, xine requires either a fast CPU with a fast video card, or support for the XVideo extension. The GUI is usable, but a bit clumsy.

As of this writing, there is no input module shipped with xine which will play CSS encoded DVD's. There are third party builds which do have modules for this built in them, but none of these are in the FreeBSD Ports Collection.

Compared to MPlayer, xine does more for the user, but at the same time, takes some of the more fine-grained control away from the user. The xine video player performs best on XVideo interfaces.

By default, xine player will start up in a graphical user interface. The menus can then be used to open a specific file:

`%` `xine`

Alternatively, it may be invoked to play a file immediately without the GUI with the command:

`%` `xine -g -p mymovie.avi`

#### 7.4.2.3. The transcode Utilities

The software transcode is not a player, but a suite of tools for re-encoding video and audio files. With transcode, one has the ability to merge video files, repair broken files, using command line tools with `stdin/stdout` stream interfaces.

A great number of options can be specified during the build from the `multimedia/transcode` port, we recommend the following command line to build transcode:

`#` `make WITH_OPTIMIZED_CFLAGS=yes WITH_LIBA52=yes WITH_LAME=yes WITH_OGG=yes \ WITH_MJPEG=yes -DWITH_XVID=yes`

The proposed settings should be sufficient for most users.

To illustrate `transcode` capacities, one example to show how to convert a DivX file into a PAL MPEG-1 file (PAL VCD):

`%` `transcode -i input.avi -V --export_prof vcd-pal -o output_vcd` `%` `mplex -f 1 -o output_vcd.mpg output_vcd.m1v output_vcd.mpa`

The resulting MPEG file, `output_vcd.mpg`, is ready to be played with MPlayer. You could even burn the file on a CD-R media to create a Video CD, in this case you will need to install and use both `multimedia/vcdimager` and `sysutils/cdrdao` programs.

There is a manual page for `transcode`, but you should also consult the transcode wiki for further information and examples.

### 7.4.3. Further Reading

The various video software packages for FreeBSD are developing rapidly. It is quite possible that in the near future many of the problems discussed here will have been resolved. In the mean time, those who want to get the very most out of FreeBSD's A/V capabilities will have to cobble together knowledge from several FAQs and tutorials and use a few different applications. This section exists to give the reader pointers to such additional information.

The MPlayer documentation is very technically informative. These documents should probably be consulted by anyone wishing to obtain a high level of expertise with UNIX® video. The MPlayer mailing list is hostile to anyone who has not bothered to read the documentation, so if you plan on making bug reports to them, RTFM.

The xine HOWTO contains a chapter on performance improvement which is general to all players.

Finally, there are some other promising applications which the reader may try:

- Avifile which is also a port `multimedia/avifile`.

- Ogle which is also a port `multimedia/ogle`.

- Xtheater

- `multimedia/dvdauthor`, an open source package for authoring DVD content.

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