4K网络直播工作流程:获取到交付

如果你像我一样, then just when you think you have mastered your HD 1080/60P workflow for live production, 你意识到你已经需要将工作流程转移到超高清4K. 在本文中, we’re going to take a first look at what it takes to work in 4K from acquisition to live webcast delivery, 以及介于两者之间的一切.

采集分辨率和帧率

The first big consideration in your workflow is if you can settle for a 30P workflow or if you require a 60P one. This one question is likely to have a big impact on your equipment choices down the workflow line. 在收购端, 大多数产消者, 入门级专业, 早期的4K/UHD摄像机型号限制在30P 4K, 即使他们也可以制作60P的高清.

Delivering in 30P might be fine for most talking-head content where there is not much action, but sports content can benefit from a higher frame rate when you’re trying to avoid intraframe blurring. Content that you want to replay in slow motion is also a good candidate for a higher initial frame rate, 尤其是当你考虑到60P是2的时候.比24P镜头快5倍. In other words, when you play back 60P footage on a 24P timeline, you can slow the footage down by 2.5倍而不复制任何帧.

One big workflow consideration for all live video content is which video camera(s) you select for the job. I find that many creative producers often overlook live workflow considerations like the availability of a live 4K HDMI or HD-SDI output. Although I do wish that my Sony X70 and FS5 video cameras supported 4K output from the HD-SDI connection, 这两款流行的机型都只有3G HD-SDI输出, 限制在1080/60P. 4K/UHD需要6G HD-SDI支持30P, 12G HD-SDI支持60P, 而索尼还没有把这一点放在首位. 6G and 12G HD-SDI connections for 30P and 60P UHD signals are more common on 4K Blackmagic Design video cameras such as the new URSA Broadcast.

It isn’t the end of the world to be starting your 4K workflow from an HDMI connection, 这是我的索尼相机和许多其他相机所支持的, 但请注意，你只能使用4K/30P. 这是, unless you move to the Sony FS7 line of cameras or use the RAW output from a camera like the Sony FS5 at 4K/60P (only the RAW output supports 4K/60P) and pair it with monitor/recorder like the 原子忍者刺客 to convert the RAW signal into an output like 12G SDI or 4K HDMI (下面的图1).

图1. 原子忍者刺客

The 原子忍者刺客 is the first 4K monitor and recorder that can record RAW from Sony, 松下, 和佳能的视频摄像机都采用了新的ProRes RAW编解码器. (ProRes RAW只能在Final Cut Pro X中编辑.)

I would prefer to work with standard HD-SDI because it supports longer cable runs and has locking bayo网 connectors. 您可以将4K HDMI转换为HD-SDI或光纤以进行更长的运行. One other HDMI solution to overcome the 25′ HDMI limitation is to use the $39 Magewell HDMI 4K Mini Repeater to extend your HDMI cable run another 25′ (下面的图2). The Repeater can often draw sufficient power from the HDMI signal but can also be externally powered if needed.

图2. Magewell HDMI 4K迷你中继器

如果我必须使用HDMI, I prefer working with a full-size HDMI connector because they are more common and I have plenty of them and they are easy to replace in a pinch if you need to. 我不喜欢使用迷你或微型hdmi线, which is what some smaller mirrorless 4K video cameras like my Sony a7S II use. I dislike the smaller HDMI variants because I find the cables are much lower quality and need to be replaced far more frequently. My own experiences with bad micro- and mini-HDMI cables isn’t isolated—in fact, one of my local camera rental stores has a policy to always send two micro-HDMI cables with Sony a7S models they rent because the cable failure rate is much higher than with standard HDMI cables.

也, I find that the micro-HDMI cables also generally come in shorter cable length runs of 3′ or less, which is fine for an on-camera monitor/recorder but not great when the camera is 5′ up on a tripod and you need to connect the short cable to some type of signal converter or distribution amplifier that you inevitably need to gaff tape to your tripod.

One final note on outputting a 4K HDMI signal from most Sony video cameras: Most models cannot record 4K internally at the same time as displaying video on the LCD/OLED viewfinder and outputting a 4K HDMI signal. 如果你需要索尼摄像机的4K画质，并且想要记录下信号, 你需要添加一个外部4K显示器/录像机.