Shooting for Streaming, Part 4
This article discusses the respective streaming quality produced by interlaced and deinterlaced source videos. Before I started this article, I knew two things for sure.
The first was that if you’re shooting for streaming, and have full frame rate (24fps or higher) progressive capabilities, you should definitely shoot in progressive mode.
The second was that if you’re buying a camcorder for streaming, you should buy a camcorder with progressive capture capabilities (like the Canon XH A1 I used in my tests).
What I didn’t know was whether to recommend ditching your interlaced-only camcorder (like my Sony HDR-FX1) in favor of a progressive camcorder if you are currently shooting for streaming. Since affordable, high-quality progressive camcorders are still relatively new, this is a critical issue for many producers equipped with interlaced camcorders. As with many quality-related issues, the answer is a definite "it depends."
There has been a tempest in a teapot regarding whether the 30F output of the XH A1 is "true" progressive. Certainly, reasonable minds can differ, but in my view, progressive video is any frame where all lines were shot at the same time. Whether this is accomplished via true progressive CCDs or by simultaneously capturing both fields in an interlaced CCD doesn’t seem to matter. My tests, which proved the benefit of shooting in progressive mode over interlaced mode in several clearly delineated circumstances, further confirms that the XH A1 produces progressive frames.
Let me give you the Cliff’s Notes version right away. In a controlled office environment, with relatively low motion and low detail—pretty much your standard set-based streaming shoot—you’ll see little difference if shooting between progressive versus interlaced mode, even with a high-energy performer like John Madden or Dick Vitale.
If you’re shooting sports or other high-motion video outside or under very good lighting, where you can sustain a high shutter speed, put your interlaced camcorder away and buy a progressive camcorder. Finally, if you frequently shoot under conditions that you can’t control, like documentary subjects, roving podcasts, and the like, a progressive camcorder will likely also improve the quality of your streaming video.
Let’s discuss the theoretical background of interlaced vs. progressive shooting, and then we’ll have a look at my tests.
As you probably know, analog TVs don’t display 29.97 frames per second; they display 59.94 fields per second, with the first field of each frame containing odd lines (1, 3, 5, 7, etc.) and the second field even lines (2, 4, 6, 8, etc.). This interlaced display technique was deemed necessary to promote smoothness during the early days of television.
On traditional interlaced camcorders, these fields are captured 1/60th of a second apart. This obviously works well when playing back on interlaced television sets, but creates problems for streaming formats, which are all progressive formats, and display complete frames from top to bottom, not fields.