Improving Quality of Meeting Recordings
By Tolga Kilicli, Product Owner, Microsoft
We released the Lync 2013 client for Windows almost a year ago, which included some changes to how calls and meetings are recorded. Those changes included introducing MP4 as the recording format to make recordings more broadly accessible across different devices and applications. As a side benefit, MP4 recordings are processed much faster on Windows 8 thanks to support for hardware acceleration.
We also discovered and received feedback on some problems with the recording feature in Lync 2013, principally:
- Meeting recording files got larger – too large to be uploaded or easily shared, which is important to people who use Lync recordings for training or knowledge sharing.
- Meeting recording quality got worse, much worse in some cases.
- These issues are interrelated – higher quality recordings usually result in larger files, all else being equal. We made some changes in a subsequent update to Lync 2013 for Windows (the CU2 update), which fixed the size but made quality even worse.
So we took a harder look at the different parameters for meeting recordings – what we could change, and why. We looked more closely at the nature of what is being recorded, in terms of screen refresh and motion and text and graphics resolution.
Analysis and user testing
Based on our analysis and useful customer feedback, we calculated a new set of recording resolutions, frame rates, and bitrate ranges. We aimed to increase the resolution of recordings yet also provide smart tradeoffs with recording size, so we landed on 3 different resolutions options: 480p (854x480 pixels), 720p (1280x720) and 1080p (1920x1080). We also increased the frame rate from 10 to 15 frames per second – not quite movie quality, but sufficient to capture PowerPoint animations and document scrolling. That improved frame rate plus the resolution options were designed to produce sufficiently high-quality recordings and yet allow users to pick their preferred balance between recording resolution and file size.
But how would that work in the real world? Before shipping an update to Lync client recording, we tested these options and few others by taking a set of real meetings and creating recording using a range of settings. We also varied the maximum bitrate of the recording, which impacts both quality and file size. Then we came up with perceptual measures of video quality, such as readability of text, animation smoothness, and image clarity.
We talked to a small group of users, had them watch different versions of the same recorded meeting (with different options), and asked them to rate each video for each perceptual measure. The results are shown below:
These results led us to a few conclusions:
- The 15 fps frame rate is necessary for sufficient quality, regardless of resolution.
- Lower bitrate (kbps) for lower resolutions does not cause a significant decrease in quality.
- Increasing bitrate without changing resolution improves quality up to a point but beyond that point quality does not significantly change.
We then finalized the options that are now available in the latest update of the Lync 2013 client for Windows:
|Resolution||Bitrate, Frame Rate||Estimated file size for 1-hour meeting (observed on Windows 8*)|
|480p (854 x 480)||500kbps, 15fps||150MB|
|720p (1280 x 720)||1250kbps, 15fps||250MB|
|1080p (1920 x 1080)||2500kbps, 15fps||400MB|
Which option to choose?
We worked on the 720p resolution to provide a good quality in a size that would fit in SharePoint 2013's default max file size limit for uploading to lists. Even though file size is dependent on the content in the video, in our tests for regular meetings we have seen 1-hour, 720p recordings to be less than 250MB on Windows 8 PCs. Also if you are using SkyDrive Pro, you can share your videos by just putting them in the local synchronized folder and sharing them with your colleagues. SkyDrive Pro also offers 25GB storage and 2GB upload limit with SharePoint Online.
For a meeting that did not have much content shared, or if file size is more important for you compared to readability of text or fine details on the content shared, you might want to consider the 480p resolution.
On the other hand, if you intend to view or present the recording on a large screen (wall display, TV), and you have multiple things being shared in addition to videos of participants (e.g. screen sharing), then the 1080p option will work much better. And the 720p option sits in the middle as the default choice and gives decent quality, decent file size, and decent resolution for most users.
To change the option used for your recordings, go to the Lync Options dialog (Tools > Options) and find the Recording tab:
Recording Manager follows these settings and when you "Publish" a meeting to an MP4 file the output will be in your selected resolution:
This also gives you an option to change the resolution in the options dialog and "Publish" your meeting again in the resolution.
We look forward to hearing your feedback on these updates and improvements to the recording feature.
*Codecs shipped in Windows 8 provides more granular control over encoder parameters. File size might be different and higher on Windows 7 as a result.