Industry Perspectives: Keeping an Eye on Video Quality
Where possible, it is often worth applying two-pass encoding to the process. Two-pass encoding is a process whereby a video file is analysed in one pass before the second encode pass. The analysis pass allows the encoding system to more efficiently apply compression to the file which results in better quality video overall. This does take additional time as the encoding system will have to do twice the work but the results are significant at the sort of bitrates being used by many online platforms these days, for example 700Kbps.
Don’t Forget About the Audio!
Audio is an area often overlooked when dealing with online video, but it is hugely important. Some subjective quality tests we have done show that an audience can rate a video to be of lower visual quality when in fact the difference in quality between the two test files was only relative to the audio.
When browsing video online one will find a wide variation in the audio levels of different video files—some loud, others quiet. This requires us to constantly adjust the volume setting of our computer for example. This is an important consideration for companies who are publishing a lot of video online that may be from a range of suppliers, as there is no standards for the industry, one must try to balance these issues into the technical plan. Normalisation of audio levels is the term applied to creating a consistency of volume for video content, another step in a well designed encoding process.
Another consideration for audio when encoding from tape is that broadcast video standards treat audio as channels, not a simple L+R mix that we create within a digital video file. This conversion needs to be balanced properly during the encoding process.
These three areas should provide an introduction into the areas of consideration when driving for quality of online video, whether you encode video yourself or have someone else do it for you.