If a video file is too large to fit conveniently fit on a storage device or transfer over the Internet in a timely manner, video editing and converting software can adjust the content to decrease file size. A video file's size is determined by the compression bitrate and the length of the content -- reducing either will shrink the file. The bitrate is a measurement of how much data a media file uses every second and is usually measured in kilobits or megabits.
Trim Unnecessary Content
Shorter videos use less space than longer videos using the same bitrate. A 2-minute video file is half the size of a 4-minute video when both use the same bitrate. Video-editing software usually lets the user trim and cut content from a video: the file size can be reduced by removing any video content that's unnecessary. For example, someone could cut the three minutes before the guest of honor entered the room from a surprise party video recording and only include a few seconds of video from before the guest arrived.
Lower the Video Bitrate
If the video doesn't have any content that can be cut, the next step is to use video editing or compression software to render the video over again with a lower data bitrate. For example, a 1-minute long video recorded at 2 Mbps takes up twice as many megabytes as a one minute long video recorded at 1 Mbps. However, the lower the video bitrate drops, the lower the video quality. YouTube recommends using 2.5 Mbps for DVD-resolution video and 5 Mbps for HD 720p video content for good video quality. Encoding.com says DVD resolution video can comfortably go as low as 1.25Mbps and 720p video can go as low as 2.5Mbps, which are commonly used bitrates for streaming content.
Lower the Audio Bitrate
Video files use separate tracks for video and audio content, so the audio content bitrate can be dropped independently of the video content to reduce the file size. For example, a high-quality video may have the audio track recorded in 320 Kbps AAC, but a video-editing program could be used to convert the audio track to 128-Kbps MP3 with a hardly noticeable difference to the viewer. Dropping the audio bitrate from 320 Kbps to 128 Kbps would reduce the file size by almost 170MB for a two-hour video.
Compensating for Lower Bitrate
There are a few methods that can help improve video quality when using a lower bitrate. If the editing or compression software supports it, use a variable bitrate instead of a constant bitrate. Variable bitrate lets the program create higher-bitrate video in parts that could benefit and reducing bitrate where higher bitrates don't improve quality. Additionally, lowering the video resolution and frame rate can improve overall image quality at a lower bitrate.
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