Industry Perspectives: Keeping an Eye on Video Quality
The following 3 areas are most important in the encoding of video:
Find the best source available
The quality of any encoded video file is relative to the quality of the source from which it has been encoded. Any degeneration introduced through the application of compression will remain visible through any futher lifecycles of the content.
It is important to remember that DVD is already a compressed digital media, and so ripping files off DVDs and encoding them will not provide a result that can be delivered from a Digibeta or similar production format. Getting back to the highest-quality version as your source is a key objective if you wish to get the best quality.
Transcoding existing compressed video files also presents significant quality issues, and providing an already compressed digital file as the source to create files of a different format or bitrate will result in further degeneration of the signal quality.
All codecs compress video data in different ways; when you have multiple encoding cycles you aggregate the negative effects of all of the codecs used. This issue is seen again and again online with video files being flipped from one format to another depending on the platform, the result is video that is blocky and lacking clarity being delivered at the expense of video that could look pretty good had it been handled well.
Create a High-Resolution Digital Master—If this is OK, then Encode!
A common phase these days is mezzanine file; it refers to a "clean" digital master which is used to create copies for streaming or download. The mezzanine file is typically a high-bitrate digital file using a production codec (for eg MPEG 50i or uncompressed AVI). This file is then used to create proxy files—repurposed versions of the master file created with specific technical settings—usually created through an automated or batched process.
When creating the mezzanine file a number of key steps must be taken, such as removing slates and breaks from a broadcast master tape, and cropping the frame to exclude edge noise that may be present. Cropping can also be applied to exclude any misalignment that may be present in the edge of the frame as a result of the content using different sources with different screen dimensions being edited together.
Once this master mezzanine file has been created, you are ready to encode for online video. During the process of encoding tests should be carried out to check the effectiveness of the de-interlacing algorithms used and the efficiency of the video compression applied.