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What is a Codec? What is a Container Format? Temporal vs Frame Based Codecs Screen Resolution Frame Rates Workflow
…and then, at the end, making sense of it all!
Why will your PC play some video files and not others? It’s all down to codecs
So why do we need codecs?
Video takes a lot of storage space on your PC/Mac
For instance 3 minutes of captured Full HD camcorder footage uses about 1gb of storage
On the plus side,storage is now cheap
The trouble really comes when trying to distribute the footage
People don’t want to be given hard drives to plug in to their TVs. They want DVDs, iPod videos, Sky+, Freeview & YouView
So the files need converting to suit these media
...the trouble is that there are hundreds (thousands?) of compression options!
But let’s start at in the 1950s...
Way back in the 1950s three main broadcast standards were established by various countries:
PAL (in the UK) NTSC (in the USA) SECAM (in France)
...and they all worked quite happily for the next thirty years!
This was mainly because video production was expensive and made by a small number of companies. Thus easily regulated.
Then in the 1990s came digital!
The Digital Revolution of the 1990s made video production cheap and available to the masses.
This made it difficult (impossible?) to regulate.
New digital ‘standards’ were required, and lots of options competed...
Instead of being imposed like the 1950 standards, the new standards were in competition with each other
The theory was that the best standard(s) would become dominant
The actual result was a minefield of formats, containers and codecs...
Codec stands for Code / Decode
It is basically a computer program that en-codes video to a specified format
From this point on the same codec is needed to play (decode) the video
The trouble comes when you move your video to another computer...
...if that PC/Mac hasn’t got the required codec installed (to decode the video) then your video won’t play.
Tip: PC users can try ‘G-Spot’ (freeware) to identify the codecs used by a video
Sorenson 3 H.264 Cinepak
Oh, and there’s an another pile of codecs for encoding audio files!
...eh, what about Quicktime and AVI?
Here’s the big confusion: Quicktime, AVI and Flash Video are not codecs!
These are ‘container’ formats.
This basically means that they contain codec compressed video and audio in one easy to play file.
Video codecs can be broadly split into two types:
Frame-based codecs Temporal (or field-based) codecs.
Video codecs can be broadly split into two types:
Frame-based codecs Temporal (or field-based) codecs.
Say What!?!
Well known examples are Cinepak and Motion-JPEG
They work by examining and compressing each frame of video individually
They have two main disadvantages: They can be slow to encode File sizes can be quite large
=Tim
e
The best known is MPEG-2 (used for Digital TV & DVDs)
They watch how much a video clip changes from frame to frame then compress only the changes between the first full frame (a keyframe) and the following frames.
Thus keeping file sizes down!
=+++
Keyframe
+++
=
Copies unchanged parts of the keyframe
The quick answer to this question is to use the relevant presets within your editing software:
But it’s always worth checking with your client about their requirements.
Especially if they’re planning on showing the video overseas.
This is where programs like Apple’s Compressor come into play (but that’s another presentation for another day!)
...no, it’s not over yet!
So we know about codecs, container formats, and how they encode video & audio files...
...but we still need to mention Screen Resolution (or how big the screen is)
All TV and DVDs in the UK used to use the same Screen Resolution: 768 x 576:
768 pixels576 pixels
Digital Video (from about 1995) reduced this to 720 pixels which were then ‘stretched’ to cover the ‘missing’ 48 pixels:
576 pixels
It doesn't matter if you watch TV on a 12” portable or fill a wall with a video projector – you don’t get any more pixels!
All this was true until thearrival of High Definition
...but guess what...
...there’s competing formats (again)!
HD Ready means that the screen resolution is: 1280 x 720 pixels
HD Ready means that the screen resolution is: 1280 x 720 pixels
Notice the change in shape – this is called Aspect Ratio
HD Ready means that the screen resolution is: 1920 x 1080 pixels
What this means is: Photos used in videos must be at least the size of
the video resolution used
Or this happens:
Minimum of 3 megapixels
Not big enough for HD!
HD needs 1920 x 1080
Each frame is made from two images spliced together:
- Tends to be used by tape based cameras- Good for fast moving action (sports)
Each frame is a single image:
- Looks more cinematic and classy
Interlaced Video displays 50 half-frames (or fields) every second.
It shuffles these in alternate rows, this tricks the eye but can look messy when paused or printed out
Note:
Horizontal Banding
1080i 1080p
Traditionally 24 fps
30 fps (actually 29.97 fps!)
25 fps
50 fps (ideally)
- That’s the complex stuff done!
1080i/50fps1080i/50fps 1080i/50fps1080i/50fps 1080i/50fps1080i/50fps
1080i/50fps1080i/50fps720p/50fps720p/50fps 1080p/50fps1080p/50fps
1080p/60fps1080p/60fps 1080p/50fps1080p/50fps 1080p/50fps1080p/50fps
640p/15fps
640p/15fps
1080p/50fps1080p/50fps 1080p/50fps1080p/50fps
720p/25fps
720p/25fps
1080p/50fps1080p/50fps 720p/25fps
720p/25fps
1080p/25fps1080p/25fps 1080p/25fps1080p/25fps 1080p/25fps1080p/25fps
1080p/25fps1080p/25fps 1080p/25fps1080p/25fps 1080p/25fps1080p/25fps
1080p/50fps1080p/50fps
Adobe Media Encoder / Apple Compressor
Adobe Media Encoder / Apple Compressor
Adobe Premiere will take care of this for you…
VideoPad does a similar thing…
Follow the Adobe Premiere handout
If Premiere is slow or exporting is taking an age, it’s probably due to bad workflow
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