常见问题

总体问题

什么是 WebM?

WebM 是一款为网络开发的开放的、无专利税的媒体文件格式。WebM 文件由 VP8 视频编码压缩的视频流和 Vorbis 音频编码压缩的a音频流组成。WebM 文件结构是基于 Matroska 媒体容器的。

什么是 VP8 视频编码?

VP8 是一款高效的 视频压缩技术,由 On2 Technologies 开发。Google 在2010年2月收购了 On2。更多信息请参阅下文“VP8 视频编码”段落。

什么是 Vorbis 音频编码?

Vorbis 是一款开源的音频压缩技术。It is an independent project of the Xiph Foundation. For more information about Vorbis, please visit www.vorbis.org.

合法的 WebM 文件只能包含 VP8 视频与 Vorbis 音频,容器必须为 .webm。你们为什么将 WebM 定义得如此狭隘?

We decided to define WebM files in this way because we wanted to do what’s best for users. Users just want video to work, they don’t want to worry about supported codecs, file formats, and so on. After much discussion with browser makers, tool developers and others, we reached a consensus that a narrowly defined format would cause the least confusion for users. If a user has a .webm file, they can be confident that it will play in any browser or media player that supports WebM.

我为什么要 WebM?

A key factor in the web’s success is that its core technologies such as HTML, HTTP, and TCP/IP are open and freely implementable. Though video is also now core to the web experience, there is unfortunately no open and free video format that is on par with the leading commercial choices. To that end, we started the WebM project, a broadly-backed community effort to develop an open web media format.

WebM was built for the web. By testing hundreds of thousands of videos with widely varying characteristics, we found that the VP8 video codec delivers high-quality video while efficiently adapting to varying processing and bandwidth conditions across a broad range of devices. VP8’s highly efficient bandwidth usage and lower storage requirements can help publishers recognize immediate cost savings. Also, the relative simplicity of VP8 makes it easy to integrate into existing environments and requires comparatively little manual tuning in the encoder to produce high-quality results.

如何播放 WebM 文件?

要播放 WebM 文件,您只需要一款支持的网页浏览器或者媒体播放器

在哪里可以观看到 WebM 视频?

YouTube 在它已有格式之外还支持了 WebM,作为其 HTML5 试验的一部分。说明见 用户页面

我如何才能将自己的视频文件转换成 WebM 格式?

创建 WebM 文件很简单。您可以使用 工具 页面中的任一款支持的软件产品。

我如何才能亲自评测 WebM 视频的质量?

Download our VP8 SDK, which includes scripts that are preconfigured to get the best out of VP8. The kit includes links to the same files used in our own testing. You can test VP8 decoding speed using FFmpeg and tools in the Chromium source tree (for example, media_bench).

Also, playback performance is still not optimized in the Developer Preview releases of the browsers that support WebM. The computational efficiencies of the VP8 codec are more accurately measured today using codec-level development tools in the SDKs. Optimizations of the browser implementations are forthcoming.

If I use publishing tools that do not handle WebM today, how should I incorporate WebM into my workflow?

Visit our Tools page for a list of open source and commercial products that support creating WebM files. In the coming weeks we will release QuickTime and DirectShow plug-ins that will enable many third-party encoding applications to produce WebM files.

我如何才能让自己的网站既能采用 WebM 也能支持其他格式?

There are open-source libraries such as the Kaltura HTML5 Media Library, Open Standard Media (OSM) Player, Projekktor, Modernizr and others that make accommodating multiple video formats in a single page very easy.

编码 WebM 视频似乎非常慢。你们打算如何处理?

For the Developer Preview we focused on optimizing the VP8 decoder. Today, encoding VP8 in “best quality” mode is the slowest configuration. Using “good quality” mode with the speed parameter set between 0 and 5 will provide a range of speeds. Best Quality is admittedly slow. We have room for great improvement on both the encoder and the decoder. We have only begun to optimize the VP8 encoder and believe that we will make very substantial speed improvements soon — especially with your help!

WebM 项目标注了“开发预览版”的标记。这是什么意思?

Today we are releasing APIs, source code, and specifications that will be useful to you if you are a developer; they are much less useful if you are not. We hope developers will use what we’ve released to build WebM as a “preview” feature in their products.

While we’re proud of our quality and performance today, there is more work to be done. The VP8 bitstream is final, but some features of the WebM format are not yet complete. We expect to achieve better visual quality and performance in an official release soon while also doing a lot more testing. You can help us get there by helping us tackle our roadmap.

Are VP8 or WebM subject to change?

The VP8 and WebM specifications as released on May 19th, 2010 are final. We believe that the code and tools can evolve and improve for many years without requiring changes to the core specifications. We’ll maintain a separate branch of the code, however, for bold new ideas that could alter the specifications. If there are significant improvements to warrant a new revision we might adopt them, but only after careful consideration and after discussing suggested changes with the WebM community.

Are you encouraging people to simply test WebM or actually use it?

The VP8 and WebM specifications as released on May 19th, 2010 are final and we encourage everyone to use them for developing applications. Google, Mozilla and Opera are all adding WebM support to their browsers and all videos that are 720p or larger uploaded to YouTube after May 19th will be be encoded in WebM as part of its HTML5 experiment. The WebM/VP8 source code and content creation tools are a Developer Preview with room for further improvement of the code. We encourage the community to help us complete the work items on our roadmap.

When do you expect WebM to evolve from the “developer preview”?

We expect to provide regular updates, and when the WebM community is sufficiently happy with our joint results and is ready to move forward, the developer preview will end.

WebM 与 VP8 是开源的。我如何获取代码和贡献代码?

The code, specifications and development guidelines are available on our Code page.

要使用 WebM 和 VP8,我一定要是程序员才行吗?

You only need to be a programmer if you want to build WebM support into a software application or contribute improvements to the VP8 or Vorbis source code. To play WebM files, all you need is a supported browser or media player. To create WebM content you can use the software listed on our Tools page. Also, YouTube is supporting WebM as part of its HTML5 experiment.

WebM 项目是归 Google 所有还是独立的? 假如 Google 改变主意了呢?

WebM is an open-source project sponsored by Google. Google licenses its intellectual property that is covered by VP to VP8 users for free, under a BSD-style license. These licenses are revocable only if the licensee files a patent infringement lawsuit against the VP8 code that Google released.

If I convert my video files to WebM, can you guarantee that they won’t become obsolete in the future?

WebM is a new format and will likely evolve over time. We will try to keep the bitstream constant and provide re-encoding tools as appropriate.

VP8 视频编码

VP8 是 Google 作为 On2 Technologies 一部分收购的那款编码吗?

是的。

如果我的显卡能加速视频回放,它能加速 VP8 吗?

The performance of VP8 is very good in software, and we’re working closely with many video card and silicon vendors to add VP8 hardware acceleration to their chips.

我可以用除了 WebM 以外的文件容器封装 VP8 或者使用除 Vorbis 以外的音频编码吗?

Yes, the license gives you the freedom to use VP8 in virtually any way you like. It should be noted, however, that when VP8 is used in a container other than WebM it will not play in browsers that support WebM.

If other applications on my system use VP8, does this mean my WebM files are compatible with those apps?

VP8 is an an open-source technology and developers are free to use it in any application, but the only applications that will play VP8 video inside WebM files are those that support WebM.

What are the limits of VP8 in terms of resolution, datarate, and framerate?

VP8 uses 14 bits for width and height, so the maximum resolution is 16384×16384 pixels. VP8 places no constraints on framerate or datarate.

WebM playback seems to use a lot of processor resources on my computer. Why is this?

The Developer Preview releases of browsers supporting WebM are not yet fully optimized and therefore have a higher computational footprint for screen rendering than we expect for the general releases. The computational efficiencies of the VP8 codec are more accurately measured today using codec-level development tools in the SDKs. Optimizations of the browser implementations are forthcoming.

WebM 视频文件格式

我如何才能知道计算机中是否安装了 WebM?

WebM 不是用来单独安装的。它包含于应用软件,如网络浏览器、媒体播放器、媒体插件等分发。我们维护有长期更新的支持 WebM 回放的产品列表

我如何知道正在观看的视频采用了 VP8 编码?

采用 VP8 编码的视频文件的扩展名为 .webm。如果您无法查看文件扩展名,请尝试读取文件属性(例如在 Mac OS 上使用 Get Info),得到的 MIME 类型应为 video/webm。如果您正在 YouTube 上播放 WebM 视频,播放器工具栏中会出现“WebM”图标。

WebM 文件是否可以在 TV、机顶盒、PVR 等设备上播放?

敬请期待!WebM 社区正与硬件厂商合作,以使更多设备支持 WebM。

有没有可以播放 WebM 文件的便捷式媒体播放器?

现在市场上还没有,不过我们正与硬件厂商合作,以使更多设备支持 WebM。

其他 Google 产品何时才能支持 WebM 与 VP8?

WebM support in Android is expected in the Gingerbread release (currently planned for Q4, 2010). We expect many other Google products to adopt WebM and VP8 as they prioritize it with their other product requirements. Keep an eye on the WebM blog for announcements.

许可

Please explain how WebM is “royalty-free.”

Some video codecs require content distributors and manufacturers to pay patent royalties to use the intellectual property within the codec. WebM and the codecs it supports (VP8 video and Vorbis audio) require no royalty payments of any kind. You can do whatever you want with the WebM code without owing money to anybody. For more information, see the License page.

What does this license let me do?

Like most BSD-style licenses, this license allows you to use the VP8 code with a minimum of restrictions on your use. You can use the code in proprietary software as well as open source software. We also offer a patent grant, whose details are discussed below.

Do I need to release the source if I make changes?

No, the license does not require you to release source if you make changes. However, we would love to see any changes you make and possibly incorporate them, so if you want to participate please visit the Code page and submit some patches.

Why didn’t you use the Apache license?

The Apache license is very similar in effect to this license in that it offers a permissive copyright license and a patent grant. The Apache license is, however, deemed incompatible with a number of projects that might make use of VP8, so we were unable to maintain compatibility with these projects and choose the Apache license.

Why didn’t you use the GPL license?

One of the goals of having this code licensed as liberally as possible is to encourage adoption by as many users as possible. This includes both proprietary and free software. Using the GPL license would not be a good match for this goal.

Doesn’t this cause license proliferation?

No. As the copyright license is simply a BSD license, and the patent
grant is fully separate from it, it is not a new license. When we first
released VP8, we had a
clause
in
the patent grant that called this into question. We’ve since fixed that
by decoupling the patent grant from the copyright license. We are
confident that this new regime is broadly compatible with permissive
and copyleft licenses.

What if I want to continue to use the first license with its extra restrictions and open source compatiblity issues?

It’s up to you, but you may be better off under the new regime.

What if someone gets the code from Google and gives it to me without changes. Do I have a patent grant from Google?

Yes, you still have the right to redistribute and you still have a patent license for Google’s patents that cover the code that Google released.

What if someone makes a change to the code and gives it to me. Do I have a patent license from Google for that change?

You still have the right to redistribute but no patent license for the changes (if there are any patents covering it). We can’t give patent licenses for changes people make after we distribute the code, as we have no way to predict what those changes will be. Other common licenses take the same approach, including the Apache license.

What if Google receives or buys a patent that covers the code I receive sometime after I receive the code. Do I have a patent grant for that patent?

Yes, you still have the right to redistribute and you still have a patent license for Google’s patents that cover the code that Google released.

What if my competitor uses the code and brings patent litigation against me for something unrelated to the code. Does he or she still have a patent license?

Yes, he still has the right to redistribute and he still has a patent license for Google’s patents that cover the code that Google released.

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