-->
为五月的纽约流媒体保留座位吧. 现在注册!

为了与电视竞争,流媒体质量必须提高的另外四个方面

文章特色图片

In 上个月的思想之流专栏, I wrote about three quality issues the industry needs to solve as quickly as possible: artifacting, AV同步, 和缓冲.

我以一个悬念结尾, not unlike what happens when an online video suddenly stops midstream and retrieves the next few seconds of video. In many instances, this is registered in player logs as dropped frames, a topic we’ll cover below.

在某些情况下, the video just stutters because the playback device can’t handle the complexity of the encoded content. Those instances aren’t measured by any media player that I know of, 但我们需要一种方法来做到这一点, as they’re the online video equivalent of “rain fade” on MPEG-2 video delivery from satellite TV. 如果发生得太多, 这在消费者中成了一个流传的笑话, one that now has enough reach to discourage potential customers from trusting satellite’s ability to deliver quality service consistently.

颜色校正

2015年下一个紧迫的质量问题, 如果我们想要达到电视质量的传输, 是颜色校准. 作为压缩过程的一部分, many codecs still use the Motion JPEG (M-JPEG) model for color space, which itself is based on JPEG imaging technologies from more than 20 years ago.

JPEG和M-JPEG格式, nuanced colors and gradients are often replaced by a single color, 由像素周围的平均颜色推导而来. 所以你不仅没有得到50个灰度, you don’t get the palette of blues or greens or reds needed to represent “normal” colors we see in reality either—or even the less-than-real television color space. Proper color calibration for online video would go a long way towards maintaining the perception of quality, 如果前面提到的问题首先得到解决.

帧速率

丢失的帧可能永远不会被完全根除, but we’ve made progress in the past 2 years with adaptive bitrate (ABR) technologies towards at least eliminating the majority of dropped frames. In recent testing I performed via Transitions for a major online media company, it was difficult to tell when dropped frames occurred without using a logging tool.

This is probably due to the fact that we’re seeing fewer instances of multiple frames dropping all at one time—although we still have the issue of buffering and stuttering, which logging systems don’t count as dropping frames if all the frames are eventually delivered—and more instances of a single frame dropped here or there. Often times a single frame drop is masked by a consistent and fluid audio track, but the industry needs to work toward a day when no frame is left behind.

延迟

如果你有理智的话, 或者只是冲动, to watch a live stream on a laptop or mobile device within earshot of a television, 毫无疑问,您面临过延迟带来的挫折. My oldest daughter recently told me she watched a live stream on YouTube of a presidential address to the nation, and was frustrated that the live stream lagged by almost 40 seconds. “在电脑上看突发新闻有什么意义?她问我.

公平的问题, because 40 seconds could be the difference between life and death if one were watching a weather report about tornadoes in your vicinity. We celebrate the fact that we can rise to TV-scale audiences with ABR streaming, but we’re sacrificing an “acceptable” delay on the grounds so we can reach a wider audience. 这是一种不可接受的权衡,需要解决. 现在.

决议

最后一个需要解决的质量问题是分辨率. It’s not enough to say that content is delivered in 720p or 1080p, if we’re using compression to extrapolate every second or third pixel. 仅仅称内容为1080p是不够的.

I ran into this issue recently while testing on online video platform: I uploaded content into the system via a “slicer” tool, which segmented the content on the local desktop and then uploaded it to the cloud for viewing. 当我回放内容的时候, 在多个网络和设备上进行测试, 它永远不会以一定的比特率播放高于720p的内容, and was noticeably softer and less crisp than the original content.

在询问公司代表时, I was told the system didn’t change the content at all before uploading it, 但当我被追问时, the representative mentioned that 1080p content is never played back at 1080p unless requested by the content owner. So much for the simplified pricing that the company touts on its website; if you choose to play the content at its intended resolution, 还有一种不同的定价方案没有公开. Not an impressive introduction to this company’s seemingly user-friendly content management and video delivery system.

结论

The seven quality topics we’ve covered over the last two Streams of Thought columns are key to bringing streaming media quality in line with television quality. The industry should pledge to take on each of these quality issues—en masse, 如果可能的话, 或零碎的, 如有必要,到2015年中期. Only then can we really begin to blur the lines between over-the-top and over-the-air television viewing.

本文发表于2014年11月/ 12月号 流媒体杂志 “网络视频的蜘蛛侠规则”继续说道."

流媒体覆盖
免费的
合资格订户
现在就订阅 最新一期 过去的问题
相关文章

视频质量 Measurement Requires Objective and Subjective Tests

How can video compressionists assess the quality of different files? Only by combining objective mathematical comparisons with their own professional judgments.

在线视频必须提高流媒体质量才能与电视竞争

There are seven glaring quality issues that still plague online video. The industry needs to get serious if it hopes to rival television in popularity.