[Google Chromecast] bhiga:
Great point. "1080" is just part of the story, "1080p" is a little more, but still not the full story. It's like calling a seamstress and asking them to make you a shirt, but only telling them "I'm male" or "I'm a tall male" - not unhelpful, but still not enough data. :)

A video file consists of:

Resolution

This is the stored or "captured" resolution, not necessarily the displayed size

Pixel aspect ratio (PAR)

The "shape" each data pixel should be displayed at. The combination of resolution and pixel aspect ratio determines the display aspect ratio (DAR), which is sometimes defined in place of PAR. Unfortunately pixel aspect ratio is not defined the same way in all formats. For MPEG and most containerless formats, it's defined by the CODEC itself. The AVI container does not have a place to store it, so AVIs will play assuming square pixels except Windows Media Player makes some assumptions about certain video frame sizes and tries to compensate (sometimes incorrectly).

Luckily, the HD and UHD resolutions use square pixels so there's less to worry about.

Field Order

Whether samples are full frames (

p

rogressive), or fields (

i

nterlaced) in upper/top field first (UFF/TFF) or lower/bottom field first (LFF/BFF) order. Sometimes you'll see field order referenced as "odd" or "even" field first, but this is ambiguous as some things label the upper field as field 0 (which would be even) while others label the upper field as field 1 (which would be odd)

Sampling rate

How many samples per second (ie, 50 Hz, 60 Hz)

Higher sampling rate = smoother motion. This is why 24 Hz content that isn't shot specifically for film rate (avoiding fast motion and fast pans/zooms) looks "jumpy" compared to "regular" video.

Bitrate

What the data rate is - usually stated in bits per second (bps), kilobits per second (Kbps) or megabits per second (Mbps)

This is what determines the size of the video portion, regardless of resolution, interlacing and sampling rate.

Bitrate and video quality go hand-in-hand. The more bits you have, the better each video frame will look.

Compression type (CODEC)

What format the video is compressed in, for example, MPEG-1, MPEG-2, MPEG-4, WMV, VP6, DivX, Lagarith, etc.

CODEC and bitrate go hand-in-hand as well. More-complex compression algorithms can provide better quality with a lower number of bits.

Container format

How the video is "wrapped" or packaged. Some formats like MPEG and Windows Media support multiplexing and can be self-contained, so they can exist outside of a container. Other formats usually exist in a QuickTime container (.mov file) or DirectShow/Video for Windows container (.avi file)

Elements from containers can be added and removed without impact to audio/video quality.

Audio compression type

Like video compression, what format the audio is compressed in, if any. Common formats include MPEG-1 Layer 3 (aka "MP3), AAC, Dolby Digital, etc. Audio can also be uncompressed LPCM, often referred to as just PCM.

Audio sampling rate

The number of audio samples per channel, per second - usually in kilohertz (KHz)

Audio sample depth aka bit depth

How large each audio sample is, usually stated in bits (8-bit, 16-bit, etc)

Audio bitrate

What the data rate is - usually stated in bits per second (bps), kilobits per second (Kbps) or megabits per second (Mbps)

This is what determines the size of the audio portion, regardless of channels, sampling rate and sample depth.

Bitrate and audio quality go hand-in-hand. The more bits you have, the closer the audio will sound to the source.

The overall size of the video portion is video bitrate x length of video in seconds

The overall size of the audio portion is audio bitrate x length of video in seconds

Add any additional metadata overhead and additional tracks (subtitles, etc) from the container (if applicable), and you have the total file size.

So "1080p" only says it's a 1920x1080 resolution, and progressive samples. It does not say what the bitrate is or display/sampling rate is.