Encoding for Online Distribution 101

Helpful and informative independent filmmaker sources

Encoding

Encoding is the format your movie is recorded, or stored, or converted to. It is a digital format used for displaying the movie. Everything on the Web is or has migrated to H.264 (an MPEG group version) as the encoding of choice for video (movies). Flash and other codecs are still around, and still supported on the Web, and Netflix is still using a proprietary form of Microsoft's VC-1 (Microsoft's old video player format). VC-1 is quite good, but not as good as H.264.

H.264 is created by the MPEG video group that created MPEG-2, which has been a digital standard for many decades. H.264 has much better compression than MPEG-2. It retains most of the original color information (4.2.2). It is backed by major manufacturers and supported in almost every browser.

Color information is also affected by how many bits the encoder outputs. Cameras with an 8-bit output are only able to store 256 colors, which is a very low color depth. You can store a larger variety of colors by increasing the number of bits used to store the colors. For example 64-bit computers are able to store and display 16 million colors. But that comes at a price. It takes a lot more bandwidth to send, and a lot more computing power to display. 12-bit cameras store over 14,000 colors, and 14-bit cameras store over 16,000 colors. It is very difficult to do color correction using only 8 bits.

H.264 isn't the end of story. H.265 encodes to around half the size of H.264, but requires very intensive decoding, which many devices may not support because they don't have a powerful enough CPU and RAM. Several manufacturers of encoders continued to work on H.264 with various proprietary enhancements. As a group, they brought those enhancements together into MPEG Dash. MPEG Dash is likely to be the next important encoder for production.

If it's video and goes online, it's best to have it in H.264 format, or MPEG Dash. Why? Because bandwidth costs money. A two hour movie in H.264 format, 30 fps, 1080p, runs around 16 Gigabyte in size. To stream that from the least expensive CDN servers is likely to cost around $4.00, and this size file will not stream to a lot of computers with low bandwidth.

Encoding affects the appearance of your movie. Encoders use compression to create the smallest possible file size, so it takes less bandwidth, whether over the air, cable, DVD, or the Internet. If you sent in MPEG-2 format with low compression, the file would be too large to send for some viewers. So compression is essential. But most compression formats are "lossy," meaning that they remove "unnecessary" picture and audio information. However, removing too much information causes a variety of problems. They are also "predictive," meaning that they expect the next frame to appear the same, and only send the information that changed.

Too highly compressed images appear blocky, splotchy, or lack detail. Blocky means that you see visible squares on the screen. You lose the impact of detail in the image. Due to prediction, you might also see parts of people's faces standing still as their faces move. In movies with fast action, or even movies with some close up action, you might see choppy movement.

The number of frames per second is also set on the camera and then the editing encoder. Low frame rates emphasize choppiness. Low action movies can be in the industry standard 24fps for NTSC (American) movies, or 25fps for PAL European movies. High action movies and sports should be in the industry standard 30fps for both NTSC and PAL. Frame rates above 30fps currently take too much Internet bandwidth. Delivery in greater than 30fps makes very little difference, unless it is sports where a lot of detail is wanted.

Note that NTSC encode frame rates are actually 1% lower than 24 or 30, while PAL frame rate is 25 fps.

Encoding is an art. Following are some things to consider on the video portion.

The masters of film have never emphasized detail on the large screen. Today's 1080p television broadcasts show far more detail than film ever did. Why were details not emphasized? Because the world of film is a fictitious environment and too much detail destroys the fictional dream. They used "pancake" makeup that hid every blemish on an actor's face. Background detail was beautiful, but rarely crisp. This was a function of the type of film used, and camera techniques that emphasize "Bokeh," showing background detail out of focus.

While it is often nice to see vivid detail in some images, it is also good not to see detail overly clearly. What experts have found is that 720p is often the best HD format for sending. If the viewers system upscales it to 1080p, it has a better appearance than the same movie sent in 1080p. Additionally, a movie that is encoded in 720p, and then given a second encoding pass in 720p, often looks better and is more compressed than the first pass.

Note that at this date, television broadcast in the US is typically 720p or 1080i, including programs on satellite and cable carriers, which requires half the bandwidth of 1080p. Blue Ray discs and online movies are in 1080p. Newer digital televisions generally can display 1080p. Televisions are not expected to have 4K resolution (4x 1080p) for at least another 5 years due to lack of demand, slow technology development, very high price, and lack of 4K content. Forget 4K TVs for five years.

For video encoding, during editing or additional compression, you should be looking at the encoded output on a large screen 1080p monitor, or close up on a 21 inch monitor, to see how it looks. Calibrating your monitor is important. Analog monitors lose brightness over the years, and LED monitors lose about 30% of their brightness in the first year. Calibrate your color and brightness levels before you start work, or you may have no idea how your movie actually looks. For LED and LCD monitors, you can use The Lagom LCD monitor test pages for calibration.

Important: Always store a copy of the original, not just the encoded version. Even the H.264 version from a digital camera should be stored as is, as the original. Edited copies never have as much of the original picture and sound information.

Next page: Encoding for smooth streaming and multiple devices.

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