Telestream, Harmonic, Sorenson, Haivision: Advanced Encoding Tips
Taking a deeper dive than most encoding and transcoding lectures do, a webinar hosted on StreamingMedia.com last week offered advanced techniques to an enthusiastic audience.
Titled "Best Practices for Advanced Encoding and Transcoding Techniques," the webinar included experts from Telestream, Harmonic, Sorenson Media, and Haivision, all of whom offered in-depth lessons in specific areas. Telestream's Kevin Loudon, product manager for Episode, started things off with a non-political definition of GOP -- "group of pictures" -- as well as definitions of I-frames, b-frames, and p-frames. Looking at H.264 specifically, Loudon explained how each type of frame plays a role in making the codec efficient. Going deeper, Loudon also explained IDR-frames, which are a special type of I-frame, that allows viewers to scrub through a video or search it without the video breaking up. He next explained special types of B-frames and told how longer and more dynamic GOP structures are good for efficiency.
Next up was Moore Macauley, director of product line management for Harmonic, who explained the anatomy of the encoding process. There are two stages, he said: preprocessing and encoding. The preprocessing stage involves a de-interlacer, a frame rate converter, a scaler, and filtering. The encoding stage includes pre-analysis (spelling out where to place frames, among other things) and rate control (which determines how to allocate bits in encoding). Preprocessing filters available include de-blocking (which removes artifacts), mosquito noise (which removes small high-frequency noise that looks likes mosquitos), and motion compensated temporal filtering (which reduced random noise). All filters work to produce better quality video at lower bit rates, said Macauley. The first two listed here are stronger for heavily compressed sources, while the last is best for lightly compressed sources.
The third speaker was Randon Morford, director of product management for Sorenson Media. After introducing Sorenson and its customers, Morford dove into methods for optimizing encoding presets. First, select and learn about the target device, he advised. As an example, he showed how to get the specs for the Apple TV and iPad, then analyze movies purchased from iTunes and get specs. A second method involves using analysis tools, such as MediaInfo, an MSU Video Quality Measurement Tool. It measure the structural similarity (SSIM) and peak signal-to-noise ratio (PSNR). That data gives information on speed and quality, showing how to create an optimal fast encode without sacrificing quality.
Finishing up the webinar was Peter Forman, vice president of business development for Haivision. Forman spoke about the tools his company applies after the codec in live streaming workflows, which result in more nimble live environments. Looking at first-mile challenges, Forman said that insufficient or unstable uplink bandwidth was often a problem, requiring companies to use a satellite truck or fiber, both of which are costly. He recommended using four steps -- constant bitrate encoding, dynamic stream shaping, microchunking, and live cloud transcoding -- instead. Forman went into detail on each step, giving best practices for best results. Dynamic stream shaping, for example, came out of a need to tackle first mile bandwidth issues. It detects the available bandwidth and changes the encoding profile if needed.
During the question-and-answer session, the presenters fielded audience questions on frame intervals, adding filters, and variable bit rate (VPR), among other topics..
The entire webinar will be archived online for 90 days.
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