制作会议视频Pt. 4:现场交付和后期制作

The postproduction phase of a video project comprises the set of activities a video producer performs after the event is completed. Editing is the main activity but audio and graphics work also fall into the postproduction category, DVD制作也是如此, 视频编码, 以及网络交付. 但是当你直播你的活动时会发生什么呢? 这对电视直播公司来说并不新鲜, but more and more event video producers are being asked to perform their postproduction activities in real-time—that is, 在事件发生时现场直播.

这些新的需求通过网络直播(和, 在较小程度上, 极大地改变了捕捉事件的方式, 导演, 混合, delivered as the timeline has moved from a delayed turnaround time to as close to real-time as technology and the physical limitations that our world's physics allow. (就像声光速度一样, it still takes a few milliseconds for audio and video signals to be acquired, 转换, 传播, 和接收.)

In the previous three articles in this four-part series on 制作会议视频, 我讨论了 生产计划和设置的重要性, 视频的灯光和音频, 拍摄演示和指导现场切换事件. Now in this fourth and final instalment I'm going to discuss both traditional postproduction workflows where the event is edited after the filming and live production workflows, 特别是当它们与直播或网络广播有关时.

视频的新速度

Postproduction workflows have come a long way since I first started digital video editing with a nonlinear editing computer program in 2001. 模拟录像带被数字录像带所取代, 这是, 反过来, 被基于硬盘和闪存的媒体所取代. 尽管有这些变化, all editors need to ingest their footage before they can start editing, this used to be the first major bottleneck in the production workflow. 正如我们将探讨的那样，情况已不再如此. Capturing videotape is a linear process, so it takes one hour to capture an hour of footage. Tapeless workflows break away from linear capture times as digital footage can be transferred as fast as the media allows, 通常在线性时间的一小部分内.

Apples-to-apples comparisons get complicated when comparing new HD video formats to older standards, for the simple reason that most new codecs have a variety of data rate options. 旧的标准，如DV, DVCAM, DVCPro, 和HDV都是25mbps, 这是 only slightly higher than the 24Mbps of the highest-quality prosumer AVCHD format. But as you move up the codec food chain, codecs come in 35, 40, 50, even 100Mbps variants. Simple math will tell you that it would take about three times longer to transfer a minute of 100Mbps DVCPro HD footage as it does to transfer a minute of XF Codec footage from Canon's new XF300/305 video cameras, 设置为35Mbps时, but this ignores the speed at which the card can theoretically transfer footage, 如果有必要转移的话.

在速度的高端是新的索尼SxS-1存储卡, 哪些承诺达到了1的传输速度.2 gbps. Now be careful not to confuse Gigabits per second (Gbps)with Gigabytes per second (GB/sec), as 1.2 gbps转换成0.15GB.每秒(或150MB/秒). These transfer rates don't really start to mean much until you translate it into a larger time unit: 1.2gbps也相当于每分钟9GB. 再做一点数学运算，我就知道只需要7个.1 minutes to transfer a full 64GB (the largest available card capacity), 这是 a full two hours of footage using the highest quality 50Mbps codec in Sony's XDCAM lineup, 或者刚好超过4.7小时的SD DV 25Mbps编解码器. 令人难以置信的是，这转化为前所未有的1.5 minutes to capture an entire hour of the same DV footage that it used to take an entire hour to capture (and when you factor in the tape rewind time the SxS-1 footage would likely be ready to edit before the tape's footage was even ready to begin capturing).

还有什么比快速传输时间更好的呢? 完全没有传输时间. Most of the flash memory formats can be edited straight from the card, 甚至没有被转移到计算机的硬盘驱动器. Whether or not this is practical or not depends on the speed of the card and its corresponding ability to serve up the video files fast enough for smooth preview and editing.