Compress Video File Without Losing Quality: What You Need to Know

Video compression is a process that reduces the file size of a video in order to save space or to stream it smoothly. Depending on their length and resolution, videos can grow to several gigabytes in size and take up a lot of space on a hard drive. They're also much too big to send by email or stream on a website. To carry out these tasks, the data within the video must be reduced in size – in other words, compressed.

An uncompressed video would produce an enormous amount of data. A one-minute long HD video with 1920 x 1080 resolution requires 10.5 GB of storage space, while a single uncompressed movie in HD quality would take up more than a terabyte of storage space. 4K videos require about four times more storage space, 8K eight times more.

Video files, such as those filmed with a camcorder, are almost always already compressed. But they're still far too large for streaming online, so they need to be compressed further beforehand.

You first need to load your files into video compression software and export them with the right file format and codec setting. But which file format and codec settings should you choose? And what's the difference between file format and codec, anyway? We explain all this and more below.

The answer is yes, it can downgrade the quality of your video. However, there is usually no way around reducing the amount of details in your video, because lossless compression simply isn't very effective for videos. The good news is that modern codecs can limit this loss in quality.

The basic rule also applies to modern codecs: The more compression is required, i.e. the smaller you want the file size to be, the greater the effect on video quality.

Lossless video codecs are available too – these preserve the original video in full quality. At first, this sounds good. But if you use these codecs, you'll also need significantly more storage space. The purpose of codecs is to reduce the required storage space to make it possible to stream your video, or use it in other ways. As a result, lossless codecs are rarely used for video, simply because they are too inefficient and produce files that are too large.

The situation is different in the audio sector, where the FLAC format (Free Lossless Audio Codec), as well other audio codecs, enable efficient compression without affecting the sound quality.

Anyone who edits videos using a computer has to work with different video formats – from older formats such as AVI and MPG or newer MP4 files to WMV, AVI, MOV, FLV, MKV and a thousand other file extensions. Every software or hardware manufacturer develops their own file format – that's why there are so many different video formats and file extensions available. Since most file formats use the same compression methods, however, there aren't a ton of technical differences. This reason for this is that while there are thousands of file formats, there are only a few compression methods.

Many of these file formats are known as containers, because they contain data that can be packaged in various ways. For example, an MP4 file can contain video data with the codecs H.265, H.264 or even MPEG-2 and even MPEG-1, as well as image data with the codecs JPG and PNG and audio with the codecs MPEG-4 Part 3, AAC, MP3, MP2 and MP1. This means that with container formats like MP4 or AVI, you don't know exactly what data is included.

Which file format should you choose? If you want to be able to play a compressed video file on many different devices, we recommend MP4 files with H.265 or H.264 for the video data and AAC or MP3 for the audio. This combination of file format and codecs ensures high video quality and a small file size, and it is currently supported by almost all hardware and software players.

The codec provides the compression method used by the file. The codec is the "language" of the video, which contains the information used to combine bits and bytes into a video image. A major function of codecs is to save space, which is important for streaming. Some codecs offer low encoding and decoding bitrates to saves processor and battery power.

A codec can also be thought of as an engine that is used inside a compressed video file. Codecs mostly used these days for MP4, are the video codec H.265/HEVC or its predecessor H.264/AVC as well as the audio codec AAC for the audio data.

Bitrate refers to the amount of information a video player or video editing program needs to process in order to play back a video. The more information available, the better the video image – but also the more processing power required for playback.

This means that reducing the bitrate compresses your video. The compression rate reflects the ratio between the original amount of data and the reduced amount of data. A low compression rate results in better image quality, but also requires more storage space. So a compression ratio of 1:8 indicates that the original video data has been reduced to 1/8.

But in terms of the quality of different compression methods, compression rate has limited significance. There may well be noticeable differences in image quality between two methods with the same compression rate. This is because some more modern compression methods work more effectively and provide better quality results than other, older ones.

Bitrate is expressed in bits per second (bit/s) Other bitrate units are kilobits per second (kbit/s, often abbreviated as "kbps"), where data transfer rate equals thousands of bits per second or megabits per second (mb/s), which means millions of bits per second. A higher bitrate usually means higher image quality, but also increased file size. Lower bitrates equal smaller file size – but the quality is reduced.

Which is better? It all depends on your needs. If you need the best possible image quality regardless of file size, higher bitrates are better. But if quality is less important than smooth playback – as is the case with streaming – then lower bitrates are better.

Let's take a closer look.

These two terms look very similar, so let's explain how they're related. As already mentioned, the frame rate is the number of video frames displayed per second. Most countries in Europe broadcast at 25 frames per second as standard, while 30 fps is the norm for North America. The human eye perceives this rapid sequence of frames as a moving image.

Since the video plays through the frames so quickly, only a small part of each image changes, but not the entire image. Most areas in the video do not change every 1/25 of a second – the sky in the background remains the same, the colors and lighting conditions too. Only the position of the objects might change a little.

Compression makes note of these minimal changes from frame to frame. Instead of storing the entire frame, it stores only the changes that it has detected. Since it stores less information, it also ends up reducing the file size. This means that very large videos can be converted into much smaller videos.

Storing less information only affects the bitrate, not the frame rate. You can lower bitrate for static frames without noticeably losing quality, but more fast-paced action frames require higher bitrate because things are changing faster in the frame. In all cases, the frame rate remains the same at 25 fps (in Europe).

It's best to use a modern codec that lets you use a variable bitrate. The file format MP4 is an example of a modern codec. You can more precisely define your options when using this format too. You can enter an average bitrate that forms an average value that the codec will keep to.

The bitrate values you should set depend on the individual video material – they're not generally applicable to all footage. That being said, we'd like to mention a useful rule of thumb here: If you lower the maximum bitrate from 24,000 to 6,000 kbps and the average bitrate from 19,000 to 3,800 kbps, you'll save a lot of data volume and (for a resolution of 1280 x 720 pixels) will usually achieve satisfactory results.

Often, you'll need to test things out first. In this case, it's a good idea to create a test project and export sample 10-second clip with different settings. Then, check out the results and project them to the total length to decide which codec setting to use for the complete video.

One more thing to remember: The audio track also plays a role if you want to reduce the video size, of course – even though file size for audio track is much smaller than that of video files.

If you choose an export format for your video, an audio codec will be set in addition to the video codec (for MP4 the audio codec is AAC). You can also change the preset values for audio codecs in the encoder settings. If you're making a music video, for instance, it's good to increase the bitrate from 128 kbps to 192 kbps to achieve better sound quality. This increases the file size too, but not by much.