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[翻译]探究为何各种H.264编码器表现良莠不齐

2009年12月13日 Galaxy 没有评论

http://share.dmhy.org/topics/view/hash_id/7c3fae1b8e8b826c7c72b8c283ef5e6e5cef1620
http://x264dev.multimedia.cx/?p=164

Why so many H.264 encoders are bad ?

橘化为枳
——探究为何各种H.264编码器表现良莠不齐

作者:Dark Shikari(作者系x264主要开发者之一)
译者:ssnake
校对:秋月
关键词:H.264、失败、视觉心理学优化、率失真优化
原标题为Why so many H.264 encoders are bad(为什么许多H.264编码器表现糟糕),原文链接:http://x264dev.multimedia.cx/?p=164

如果潜心钻研各种H.264编码器,你无疑会发现其中表现糟糕者不在少数。当然,也不必惊讶于此,正如史特金定律告诉我们的:任何事物,其中九成都是垃圾(原文:90% of everything is crap.(Wikipedia作crud,意义接近))。而作为多年来最为公允的视频标准,支持H.264的软件不可胜计,绝对数量的巨大使得其中必然有相当数量的劣质实现方案。

但这并不足以解释优劣H.264编码器之间的鸿沟。优秀的H.264编码器——比如x264——在许多案例中可以以仅仅一半的码率击败上一代的编码器(比如XviD);而劣质的H.264编码器甚至糟糕到会输给MPEG-2!不同实现方案的差距会如此之大,这似乎是之前的各种标准从未有过的情况……当然,这里我们找到了一些缘由。
阅读全文…

分类: 译言翻译 标签: , ,

外国人看不到的中国审查

2008年8月21日 Galaxy 没有评论

http://www.yeeyan.com/articles/view/Elaine%20Lu/12525

简介

       自北京城报导奥运的外国记者发现进入海外知名网站受阻后,北京的网络监管问题近来频频见诸报端。现在政府已经解封了其中一些网站,但是更大的问题已经得到了解决吗?中国对普通百姓的电子通讯审查的变化有多少呢?

自北京城报导奥运的外国记者发现进入海外知名网站受阻后,北京的网络审查问题近来频频见诸报端。虽然现在政府已经解封了其中一些网站,但是记者们可不要认为更大的问题已经得到了解决。中国对普通百姓的电子通讯审查变化甚微。来访的记者们忽略了这一点,是因为不熟悉这些针对中文内容的审查形式:网站和服务的主机使用的是中国国内的计算机服务器。而一般而言外国人并不使用。

中国过滤系统,俗称“长城防火墙”,阻止的各类网址和关键字实际上都是来自国外的计算机服务器主机提供的网站和服务。在中国国内,拥有自己网站、博客和聊天室的公司必须为其服务发表的反对内容负责。中国所有的博客服务、YouTube类型的视频共享网站之流,都有一整个部门来标志或删除麻烦内容,否则会被政府部门吊销营业执照。

这个背景对于理解中国人的博客和聊天室中大量的政治性谈话非常关键。确实,和几年前相比,大众关注的公共话题讨论有了更大的空间。然而这样的空间仍旧是有限制的。中国网络用户受到的网络审查比以前更有针对性更隐晦。

例子很多。周一,我登陆数个中国博客服务网站,基于美国媒体对上周美国游客在北京鼓楼遭遇刀袭的报道,用中文发表第一段。中国最受欢迎的博客平台之一—新浪,几小时后删除了我发表的文章。但是新浪新闻门户网站上登出了中国新闻社有关此次袭击的报道。百度,中国最大的网络公司之一,其经营的博客服务甚至不允许我发表这篇文章。然而,在百度新闻中搜索“鼓楼”后,跳出好几个中国媒体对这个事件的报道。

策略似乎很清楚:放松对中国的专业记者的管制,让他们报道突发新闻,即使是负面新闻——因为消息总会流传出去,而且他们和博客不同,仍然在管制之下。同时,打击那些可能含有过多关于新闻自由讨论的博客、聊天室、视频共享网站。继贵州省瓮安县因一个年轻女孩的可疑死亡发生大暴乱之后。类似的事情上演了。许多中国大门户网站纷纷删除或阻止发表任何提及瓮安的博客或聊天室发言。相反,门户网站上则涌现了中国专业媒体对瓮安事件的大幅报道。

即使是幽默也逃不过审查。上周的一个晚上,一个笔名为“deerfang”的中国博客正和一个朋友分享笑话,那个朋友知道一些经典政治笑话,这些笑话是5月份其他朋友通过手机短信发来的。这个朋友试着把一则关于毛主席和胡锦涛主席的笑话发给deerfang。“我手机收到了信息,但是一片空白,说是‘文本缺失’”deerfang在她的博客中写到。她的朋友生怕是技术错误,又把这条信息发给另外几个人。结果还是一样。看来自从3个月前,中国移动就已经加紧了网络审查。

中国的审查制度远非刀枪不入。由于某种原因,一个网络平台上审查的内容常常会在另一个网络平台上泄露。用户可以想出替换的字眼或使用委婉的说法避免关键字被追踪或者干脆通过电子邮件四处传播新闻,他们确实是这么做的。长远看来,审查制度注定会失败。但是短期内,各种措施确实行之有效,有助于中国共产党手握大权。

外国人需要知道这就是此时此刻正在发生的事情。还有一点也十分有用:近来关于北京的审查制度尘嚣至上。目的是把注意力引到更大的问题上,而外行人未能理解审查制度对中国网络的实际影响如何,令这个国家的人民十分沮丧。本周的前几天,我收到了一个名叫杜东进的博客的来信,他抱怨道:“在我看来,美国之音的评论很浅显,它根本不介意中国是否有网络审查制度,它只在乎自己的利益。”此前他收到一封美国之音祝贺中国网络解封的电子邮件。

他的抱怨意味着,不论是增加的权利,还是解封美国之音网站,还是另外一个或是几个外国网站,对于北京的网络控制问题都不会有更多改观。外国记者在奥运会期间浏览特赦国际网站时应该记住这点。


http://online.wsj.com/article/SB121865176983837575.html?mod=opinion_main_commentaries

The Chinese Censorship

Foreigners Don’t See

By REBECCA MACKINNON

FROM TODAY’S WALL STREET JOURNAL ASIA

August 14, 2008

Beijing’s Internet censorship hit global headlines recently, when foreign journalists in town to cover the Olympics discovered their access to well-known overseas Web sites was blocked. Yet while the government has now unblocked some of those sites, those journalists shouldn’t think the broader problem is solved. Censorship of ordinary Chinese people’s electronic communications within China has changed little. Visiting reporters just aren’t noticing because these forms of censorship relate to Chinese-language content they’re not familiar with, hosted on Web sites and services located on computer servers inside China, which foreigners generally don’t use.

The “Great Firewall,” the common moniker for China’s filtering system that blocks various Internet addresses and keywords, really only pertains to Internet sites and services hosted on computer servers outside China. Inside China, companies that host Web sites, blogs and chat rooms are held responsible for objectionable content posted on their services. All of China’s blog-hosting services, YouTube-style video sharing sites and the like hire entire departments of people to flag and delete things that may get them in trouble with the government authorities who could revoke their business license.

This context is key to understanding the wide-ranging conversations, many of them political, that are now happening on Chinese blogs and chat rooms. There is indeed a vastly larger space for public discourse on matters of public concern than existed even a few years ago. But that space still has limits. Chinese Web users now experience a more targeted and subtle approach to censorship than before.

Examples abound. On Monday, I logged into a number of Chinese blog-hosting services and posted the first paragraph of a Chinese-language story, based on state media reports, about last week’s knife attack on American tourists atop Beijing’s Drum Tower. One of China’s most popular blogging platforms, Sina.com, deleted my post after a few hours. But Sina’s news portal ran Chinese news agency reports about the attack. A blog-hosting service run by Baidu, one of China’s biggest Internet companies, wouldn’t even let me publish the post. Yet a Baidu news search on “drum tower” turned up several Chinese media reports about the incident.

The strategy seems clear: Give China’s professional journalists a longer leash to cover breaking news even if it’s not positive — since the news will come out anyway and unlike bloggers, the journalists are still on a leash. At the same time, clamp down on blogs, chat rooms and video-sharing sites that might allow too much unfettered discussion of the news. A similar thing happened in July after large riots took place in Weng’an, a town in Guizhou province, after a young girl died under suspicious circumstances. Many large Chinese Web portals deleted or prevented publication of any blog and chat room posts mentioning Weng’an. Instead the Web portals ran extensive coverage of events in Weng’an reported by China’s professional media.

Not even humor is safe from censorship. One evening last week, a Chinese blogger who writes under the name of “deerfang” was sharing a good laugh with a friend who knows some great political jokes — learned through mobile-phone text messages sent in May from other friends. The friend tried to forward one of the jokes about Chairman Mao and President Hu Jintao — still stored in his phone’s memory — to deerfang’s mobile. “My phone received the message but in blank saying ‘missing text,’” deerfang wrote on her blog. Her friend tried sending the message to other people’s phones in case it was a technical error. Same result. It seems that censorship on the China Mobile network has tightened since three months ago.

China’s censorship is far from perfect. Often what’s censored on one Web platform somehow slips through on another. Users can and do devise alternate wordings or euphemisms to avoid the notice of keyword trackers, or simply email the news around. In the long run censorship is bound to fail. But in the short run this variety works just well enough to help the Chinese Communist Party stay in power.

And foreigners need to understand that it’s happening, and how. As useful as the recent uproar over censorship in Beijing was for calling attention to the broader issue, the failure of outsiders to understand how censorship affects the Chinese Internet in practice is a source of frustration inside the country. Earlier this week, I heard from a blogger, Du Dongjin after he received an email from the Voice of America celebrating the unblocking of their Chinese website. “In my point of view,” he complained, “it is quite a plain comment that VOA does not care if there is Internet censorship in China. It only cares its own interests.”

By this he meant that, whatever the incremental benefits, unblocking VOA’s site — or any other one or several foreign sites — won’t change the more problematic aspects of Beijing’s web control. That’s something for foreign reporters to remember as they surf Amnesty International’s Web site during the Games.

Ms. MacKinnon is assistant professor at the Journalism and Media Studies Centre, University of Hong Kong and co-founder of Global Voices (globalvoicesonline.org).

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分类: 译言翻译 标签: , ,
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