For those who want to learn more about digital video basics.
This YouTube video explains basic digital video construction well.
1. What is Video?
The English term "video" comes from the Latin verb "videre", which
means, "I see".
What is the difference between "Movie" and "Video"
|Movie Film||Video File|
|Purpose||Big screen by projection||Monitor|
|Frame||One frame at time||Dot(or Pixel)>Line>(Filed)>Frame|
|Big image||Easy to achieve||Resolution (pixel) limitation|
(1) Video is a sequence of still images representing
scenes in motion.
Basic idea is the same as old movie film, where the "sequence of still images representing scenes in motion" is captured on (analog) films, and the films need to be chemically developed before showing the image.
(2) Video is a motion technology of "electronically" done.
In its basic technology, movie can be captured on a film with no batteries, flashlights or no electric at all.
There was a small handle to wind up films, but no battery in an old 8mm movie film camera.
(3) Video will be "capturing, recording, processing, storing, transmitting, and reconstructing" all done electrically.
-1. Capture -video camera (camcorder) needs battery vs. Film movie camera doesn't.
-2. Record - Mostly on magnetic tape ( e.g. VHS tape), hard-drive or some forms of card (e.g. SD card).
-3. Process - Tapes or other medium will be processed with electric devices.
-4. Store - same as the recording device (2).
-5. Transmit - TV broadcast, through the Internet, LAN or WiHi network (iPad, iPhone, iPod..)
-6. Reconstruct - Movie films don't need to be reconstructed.
Why Video have to be "re-constructed"?
Because video has to be shrunk to a small size to fit on a single disc (e.g. a DVD disc) or transmittable through the Internet that it has to be restored to its original size when viewed.
You receive TV program by cable, dish or phone line; and these signal(data) will be reconstructed as image (video) on your TV monitor. Or video can be transmitted through the Internet and will be reconstructed on your iPhone.
This technique is called Codecs (explained in details here).
Movie Films need no Codecs because they are delivered by cars, trucks or FedEx to many movie theaters.
Digital video comprises a series of orthogonal digital
images displayed in rapid succession at a constant rate.
In other word, the very basic idea of video is the same as 100 years ago - it's a Flip Book, just a digital version
Let's learn terminology (words) about VIDEO, so we can talk each other smoothly.
Each image is called Frame.
The size of each frame is measured by Pixcels.
How many Frames are shown per second = Frames
Per Second (FPS).
The horizontal and vertical size are defined as number of pixels(ie 1920 x 1080).
When a TV set is sold as '1080p", it means the vertical frame size of 1080 and scanning system is Progressive.
How long is the movie.
How rich color = how many colors on each frame.
bit rate, bit
per second (BPS) = the number
of bits that are conveyed or processed per second.
Bit rate plays an important role when transmitting video because
the transmission link (such as the Internet, TV cable ) must be
capable of supporting that bit rate.
|Video Size|| Video size
= how big is the digital video file size.
It can be measured by the following formula:
Video size = Width x Height x color depth x FPS(frame per second) x runtime in seconds.
(How big is each page x how rich color it contains x how many pages per second x how long )
Since BPS (bit per second ) is the amount of info per second, Video size can be measured by:
Video size = BPS x total runtime in seconds
For example, a video of duration (T) of 1 hour (3600sec), a frame
size of 640x480 (WxH) at a color depth of 24bits and a frame rate
Let's say you are at a movie theater enjoying a movie.
With the home TV, things are not that easy because information has be transmitted through Air Wave or Wire that a whole big image cannot be sent one by one(it's too big), instead the video image has to be shrunk and sent little by little, like a half at a time.
Braking a single frame into halves, so
the beam has to run only a half distance.
This technique is called Interlace Scanning System.
Interlace technique was developed because TV technology could
not display an entire frame in one action.
Display device aspect ratio and Pixel shape aspect ratio
(1) Display Aspect Ratio (DAR)
The screen aspect ratio of a traditional(old) television screen is
4:3, however, High definition televisions use an aspect ratio
(A) Traditional(old) TV monitor is 4:3 ratio
The 4:3 ratio (generally named as "Four-Three", "Four-by-Three",
"Four-to-Three", or "Academy Ratio") for standard television has
been in use since television's origins.
Let's go back a little further.
Later in TV area, when cinema attendance dropped, Hollywood created wide screen aspect ratios (such as the 1.85:1 ratio mentioned earlier) in order to differentiate the film industry from TV.
(B) HD TV monitor ratio is 16:9
Why 16:9 ratio for HD TV?
(2) Pixel Aspect Ratio (PAR)
Pixel is short for Picture Element, and is the smallest element(unit)
on a monitor.
How to compare video quality?
How to tell one is better than other in terms video quality?
In digital video world, number of pixels rules. More
pixels, the better picture.
For example, on the same size of TV monitor, 1920 x 1080 pixels quality is better than 640 x 480 pixels image.
But in real world, however, the pixel number can be changed in computer program.
When it comes to digital conversion, the 'Garbage in, Garbage out' rule applies here.
If the original image is bad, the video image is bad no matter how big the size would be.
In an old analog video world, the pixel doesn't play a
role for judging video quality, because unlike digital video, analog
video is not made of pixels.
So what does differentiate the analog video quality?
If you can see more details on monitor, that's a better image.
To get more details, monitor needs more dots, like pixels.
With digital HDTV world, more dots means more pixels. The number of pixels rules.
With analog TV, the number of horizontal lines (vertical resolution) is fixed (NTSC is 525, PAL is 625).
How can we differentiate the image quality? - the answer is horizontal resolution.
In an old TV system, the number of horizontal lines was
NTSC (=US) is 525 lines and PAL (=Europe) is 625 lines.
If we go from the word " vertical resolution", it is independent of the system bandwidth and defines the capability of the system to resolve horizontal lines, which is expressed as the number of distinct horizontal lines.
Unlike today's HD NTSC TV system whose horizontal lines
could be 720 or 1080, in the old NTSC analog TV system, the number of
horizontal lines is fixed to 525 lines. However, because complete loss
of vertical resolution will occur when the scanning spot straddles picture
details, from subjective data, it has been found that the actual vertical
resolution is equal to 70 percent (the Kell factor) of the number of
In NTSC, there is a total of 525 lines per frame, of which about 40 are blanked, leaving, typically, about 485 active lines per frame. Given a Kell factor of 0.7, the effective vertical resolution is about 340 lines (525-40 loss) x 0.7 = 339.
You might want to call the old NTSC TV system 340i vs. 1080p(today's HD TV).
Why NTSC is 525 and PAL is 650 lines?
Why not simpler 500 or 600 even numbers?
The figure of 525 lines was chosen as a consequence of the limitations of the vacuum-tube-based technologies of the day.
In early TV systems, a master voltage-controlled oscillator was run at twice the horizontal line frequency, and this frequency was divided down by the number of lines used (in this case 525) to give the field frequency This frequency was then compared with the 60 Hz power-line frequency and any discrepancy corrected by adjusting the frequency of the master oscillator.
For interlaced scanning, an odd number of lines per frame was required in order to make the vertical retrace distance identical for the odd and even fields; an extra odd line means that the same distance is covered in retracing from the final odd line to the first even line as from the final even line to the first odd line, so simplifying the retrace circuitry. The closest practical sequence to 500 was 3 ~ 5 ~ 5 ~ 7 = 525. Similarly, 625-line PAL-B/G and SECAM uses 5 ~ 5 ~ 5 ~ 5.
Because no beam runs vertically on a TV monitor, vertical resolutions are defined by the number of dots (=elements) on each horizontal line.
Below is a list of modern, digital-style resolutions (and
traditional analog "TV lines per picture height" measurements) for various
The list only includes popular formats.
All values are approximate NTSC resolutions.
352~240 (250 lines at low-definition): Video CD
350~480 (250 lines): Umatic, Betamax, VHS, Video8
420~480 (300 lines): Super Betamax, Betacam (professional)
460~480 (330 lines): Analog Broadcast
590~480 (420 lines): LaserDisc, Super VHS, Hi8
720~480 (500 lines): DVD, miniDV, Digital8
720~480 (380 lines): Widescreen DVD
1280~720 (680 lines): Blu-ray
1440~1080 (760 lines): miniDV (high-def variant)
1920~1080 (1020 lines): Blu-ray
Now that we are familiar with digital video terminology, we can talk about digital video in real world.
1. Why digital video has to be small?
2. How to make digital video smaller?
Just think about when and how you enjoy video in your
-1. from the Internet (YouTube, CNN news...)
-2. Hollywood style movie on a DVD video disc (DVD player, PC or Mac)
-3. On your handheld device (iPad, iPhone, iPod...)
-4. Since 2009, your home TV is receiving digital video broadcast (through Cable, Dish or Phone line..)
As we learned before, a one-hour movie in standard (640 x 480) pixels is just about 82.8 GB, which means a two-hour movie comes out to be 165 GB.
A two-hour movie in HD (1920 x 1080) pixels goes beyond 600 GB.
One DVD disc can hold 4.5GB date, so it will take almost
20(twenty!) DVDs for a standard two-hour movie and 135 DVD discs for
a two-hour HD movie.
You have to change DVDs every 6 minutes with standard movie and every 1 minute with HD movie!
Your iPad, iPhone or iPod can't hold that big date.
When you want to share your home movie on the Internet, the file is way, way too big for upload.
More importantly, the information is too big to be processed and moved around inside the computer and network system.
The digital movie has to be much more compact, at least we have to reduce to the size that will fit on a single disc.
So, that's the necessity of digital video compression, and people started developing many ideas to make it happen.
Let's go back and think -"What defines Video file
Video size was defined by the following formula:
= Width x Height x color depth x FPS(frame per second) x runtime in seconds
= Frame size x number of frame pre second x runtime.
So we've realized that there are 3 elements for reducing Video file size, they are:
-1. make frame size smaller
-2. send less frames per second
-3 make the movie shorter
(e.g. YouTube is limited to 10 minutes, but logical speaking, this is too obvious, to we don't discuss this )
We talk about -2) send less frame per second, topic first, followed by -1) make frame size smaller, because there are a lot to talk about how to "shrink" frame size than reducing FPS (Frame Per Second) number.
As noted above BPP represents the average bits per pixel.
There are compression algorithms that keep the BPP almost constant throughout
the entire duration of the video.
In this case video will be output with a constant bit rate (CBR). This CBR video is suitable for real-time, non-buffered, fixed bandwidth video streaming (e.g. in videoconferencing).
Noting that not all frames can be compressed at the same level because quality is more severely impacted for scenes of high complexity some algorithms try to constantly adjust the BPP. For example, an interview movie where the background is almost the same for entire footage is a good candidate for CBR. However, in a baseball game movie, when a player is running, we can't reduce frame numbers that much so the motion gets sluggish, but frame numbers reduction is not so noticeable when the game is going slowly. In other word, they keep it high while compressing complex scenes and low for less demanding scenes. This way one gets the best quality at the smallest average bit rate (and the smallest file size accordingly). Of course when using this method the bit rate is variable because it tracks the variations of the BPP. Variable bit rate (VBR)encoding is also commonly used on MPEG-2 video, MPEG-4 Part 2 video (Xvid, DivX, etc), MPEG-4 Part 10/H.264 video, Theora, Dirac and other video compression formats.
Intra-frame Compression: Shrink each frame one by one
Shirk each frame, all of them, say 1/20 size once, then expand them back to its original size when viewing it. The file size is smaller only when stored (ex. DVD disc, on hard drive in an iPhone or up/down on the Internet), then restored when viewed. This is called Intra-frame compression.
Inter-frame compression: Shrink a group of frames for
more efficient compress. More efficient compression method from #3.
This is called Inter-frame compression.
Either one-by-one or as a group, the basic idea for compressing
Digital Video File is that we will shrink (compress ) the original video
size to 1/20 or even smaller for storage on media (like DVD or iPhone)
or during transfer period through network, and it will be restored to
its original video size when viewed.
The program for reducing the digital video file size is called Encoder, and the program for restoring it to its original size is called Decorder.
Encoder and Decorder is a pair of program that work together - Encoder is entrance where Decorder is exit.
This pair of Encoder / Decorder is called Codec.
Codec = Compressor + Decompressor = Encoder + Decorder
When we talk about "Codec", we are talking about
both compressing and decompressing a digital video file.
W also know that there are two basic different kinds of Codec, one is based on Intra-frame compression (one frame each ) or Inter-frame compression (a group of frames together).
As explained before, there are two different approaches
for compressing digital video size.
One is called Intra-frame compression and another is called Inter-frame compression.
The Intra-frame compression shrink one of each frame individually, one-by-one, while the Intre-frame compression will check a keyframe and compare many frames around that "keyframe", analyze how similar each other, and compress as a group of files.
The Inter-frame compression method's compression ratio is much larger than Intra-frame compression. In other word, you can make a video clip a lot smaller by using Inter-frame compression technique.
We will see pros and cons of both methods.
There are two well-known Intra-frame compression Codec's.
One is M-Jpeg and another is DV.
They both compress each frame individually.
The difference between them is that while M-Jpeg has flexible compression ratio setting, DV is fixed.
Let's see more details.
-1. M-Jpeg (Mjepg, Motion-Jpeg)
i) One of two popular Intra-frame compression Codec's.
ii) Good for Video Editing, because of individual frame accessibility and supports by many hard & software.
iii) Compression ratio is not high - much more than double the size of Inter-frame Codec's.
iv) Old technique, but will stay in for the future.
Mjpeg sample video (22 mb)
Motion JPEG uses a lossy form of Intra-frame compression. What basically happens here is, using a similar technique like Jpeg with still photo, Mjpeg compress each frame one by one individually.
Nearly all software implementations of M-Jpeg permit user control over the compression ratio (as well as other optional parameters), allowing the user to tradeoff picture quality for smaller video file size.
In embedded applications (such as miniDV, DVCam or DVCPro), the parameters are pre-selected and fixed for the application.
M-JPEG is an Intre-frame compression scheme (compared with the more computationally intensive technique of Inter-frame compression technique). Whereas modern Inter-frame video formats, such as MPEG1, MPEG2 and MPEG4/H.264, achieve real world compression ratios of 1:50 or better(smaller), M-Jpeg is 1:20 or lower (bigger). Because frames are compressed independently of one another, M-JPEG imposes lower processing and memory requirements on hardware devices.
As a purely Intra-frame_frame compression scheme, the image-quality of M-JPEG is directly a function of each video frame's static (spatial) complexity. Frames with large smooth-transitions or monotone surfaces compress well, and are more likely to hold their original detail with few visible compression artifacts. Frames exhibiting complex textures, fine curves and lines (such as writing on a newspaper) are prone to exhibit DCT-artifacts such as ringing, smudging, and macroblocking. M-JPEG compressed-video is also insensitive to motion-complexity, i.e. variation over time. It is neither hindered by highly random motion (such as the surface-water turbulence in a large waterfall), nor helped by the absence of motion (such as static landscape shot by tripod), which are two opposite extremes commonly used to test Intra-frame video-formats.
For QuickTime formats, Apple has defined two types of coding: MJPEG-A and MJPEG-B. MJPEG-B no longer retains valid JPEG Interchange Files within it, hence it is not possible to take a frame into a JPEG file without slightly modifying the headers.
M-Jpeg is often used for Non-Linear Video Editing system, because natively offers random access to any individual frame (no Inter-frame Codec allows this), it is a mature format, needs no special hardware on modern PCs, and , M-Jpeg is widely supported by almost all editing equipment and software.
Although the bitrate of M-Jpeg is lower than uncompressed video, it is much higher than that of video formats which use Inter-frame compensation such as MPEG-4. The large library of legacy software, low computational requirement, ease of editing ensure M-Jpeg content will be playable well into the future, even if the applications/equipment which created the content no longer exist.
For detailed specifications of Motion Jpeg, here is the link for Apple's Qick Time Format in Motion Jpeg (PDF file)
i) Good for None-Linear Video Editing, became Intra-frame compression Codec allows access to individual frames.
ii) File size is huge.
iii) Comes with different formats: DV, DVCam, DVCPro.
There is a comprehensive explanation about DV format.
The goal of the Inter-frame compression is to minimize the number of pixels that are used by a digital movie while maintaining the differences between the original (uncompressed) image and the reconstructed image very minimum, or at least same to the human eye.
The Intra-frame compression, explained before, tries to compress each frame shrunk one by one, without thinking what image next to each other.
The Inter-frame Codecs realized there are a lot can be done to shrink a digital movie by grouping multiple frames together.
|First set a home frame (= Keyframe ). Analyze how different following frames are compared to the keyframe.
Using the key frame's info, apply new image(pixels) only to different portions on following frames.
a sample movie
First, we collect detailed info of a main frame ( Keyframe).
Then, compare other frames to the keyframe.
Section D is almost identical through out the 4 frames( far up sky ) - we can use same backs.
Section A is almost same also - use most info through out 4 frames with little alternation.
Section B is very similar each other - little change will do.
Section C is tricky - left side is almost same, but right side is very different each other.
Next calculate how different next frame is, and next..among the entire group of frames.
This way, we can save a lot of digital info = we can reduce Bitrate
Quality and file size - We are getting better and better to compress digital video image:
-1. better image quality (much true to the un-compresed original)
-2. much more compact (file size is mush smaller than original video, HD movie through the Internet )
|Codec name||Resolution NTSC /PAL||Used for|
|1983||Mpeg-1||352x240 / 352x288||VHS tape to CD|
|1885||Mpeg-2||720x480 / 720x576||DVD disc|
|1999||Mpeg-4 part2||up to 1920 x 1080||Xvid, Dvix|
||up to 1920 x 1080||Quick Time, Xvid, Dvix, AVCHD, Blu-ray
Also known as Mpeg4-AVC or H.264
A container format (also called as wrapper format) is a file format whose specification describes how data(video and audio) and metadata are stored.
Although video and audio streams can be coded and decoded (Codec)
with many different algorithms, they have to work together in harmony.
Video image and audio sound have to be synchronized precisely.
So we need a someone like an orchestra director, who can synchronized moving image with sound perfectly.
Along with this synchronization information needed to play back the various streams together, like a Hollywood movie DVD, it has to handle caption subtitles, different languages, chapters and so on.
If you are given an encoded video with an encoded sound, how can you synchronize them together, or
if you try to give someone a set of video and audio files, we need standard format, under which a certain video and audio can work together properly.
Container format is necessary for organizing different
video files and audio files work together.
Simpler container formats can contain different types of audio Codecs, while more advanced container formats can support multiple audio and video streams, subtitles, chapter-information, and metadata (tags).
Don't get confused container format with Codec.
The Codec is about shrinking and restore video and audio files, while container format is to organize different (already encoded) files work to together
Let's put it in other way; In video terminology, container format is a type of file format that contains various types of data compressed by Codecs. Container formats don't specify what Codec the container format uses, but rather it defines how the video, audio and other data is stored within the container so they can collaborate well.
To drive a car in a container, you need a key for the
container and another key for the car.
To play a video in a container format, you need a key for the container (a container file) and a key for the video (Codec).
To play a Divx encoded video in AVI container format, fist you need an AVI container file, which "Windows Media Player" has it, and second, you need a key for the video, which is Decorder (Codec) of Divx. In other word, you need two things on your PC/Mac to play a video, 1) container file and 2) Codec.
AVI (Audio Video Interleave) (.AVI)- Windows
As the name suggests, AVI files can contain both audio and video data in a file container that allows synchronous audio-with-video playback. AVI was introduced by Microsoft in November 1992 as part of its Video for Windows technology.
Since AVI container was developed by Microsoft, as long
as you have Windows Media Player on your Windows system, you can open
(if you can play the contents inside the container is an issue of Codec, not AVI container itself).
It can be used for uncompressed video and audio or streams compressed with a VfW Codec. Common cadets for AVI files include DivX, XviiD and DV.
Quick Time (.MOV) - Apple
QuickTime is used by Apple's QuickTime encoding and playback software. It uses an extension of .MOV. It's also very closely related to the MP4 container, which was originally based on this container. Video streams found in QuickTime containers are generally MPEG-4 AVC, with audio typically being AAC.
Apple released the first version of QuickTime on December 2, 1991 it was an astounding technological breakthrough at the time. Microsoft's competing technology?Video for Windows?employed several thousand lines of allegedly stolen Quicktime source code and did not appear until November 1992.
"In August 1997, Apple and Microsoft announced a settlement deal. Apple would drop all current lawsuits, including all lingering issues from the Apple Computer, Inc. v. Microsoft Corp. lawsuit and the "QuickTime source code" lawsuit, and agree to make Internet Explorer the default browser on the Macintosh unless the user explicitly chose the bundled Netscape browser. In return, Microsoft agreed to continue developing Office, Internet Explorer, and various developer tools and software for the Mac for the next five years, and purchase $150 million of non-voting Apple stock." ( more details on Wikia)
MP4 (.MP4, M4V, M4V or M4P)
MP4 MP4 is the official container for MPEG-4 video, as defined by MPEG-4 Part 14. It's based on the container Apple developed for QuickTime. Extension is MP4, however, some files containing only video use .M4V and audio only will use .M4A.
.M4P is a protected files with DRM from iTunes stores.
The streams normally found in the MP4 container are MPEG-4 ASP, MPEG-4 AVC video and AAC audio.
Mpeg-2 Program Stream (.Mpeg)
MPEG-2 Program Streams is a container format for Mpeg-2 video and interleave audio streams.
The extension is either .MPG or .MPEG. These files typically contain MPEG-2 video and either MPEG-1 Layer 2 or MPEG-2 Layer 2, or AC-3 (Dolby Digital) audio.
MPEG-2 Transport Stream(.TS)
The MPEG-2 Transport Stream container is designed to deliver multiple sets of streams together that would normally have to be delivered as separate files. Rather than limiting the container to a single video stream, as most containers including the standard MPEG-2 Program Stream are, this container allows multiple video streams to be delivered simultaneously. This makes it suitable for various broadcast type applications like Streaming video across the Internet and satellite television. .TS is also used on Blu-ray Disc Video
These files typically contain MPEG-2 video and either MPEG-1 Layer 2 or MPEG-2 Layer 2, or AC-3 (Dolby Digital) audio
DVD-Video uses a variation on the standard MPEG-2 container. This is generally referred to as the VOB container, because the file extension used on DVDs is .VOB for Video Object. Although there is additional information added that's not part of the original MPEG container, most software designed for reading MPEG files should be able to read streams from the VOB container.
WMV and ASF
ASF (Advanced Systems Format, Advanced Streaming Format, or Active Streaming Format).is a Microsoft's container used for Windows Media Video and Audio streams. ASF files may have an extension of .ASF, or may use WMA or WMV denoting audio or video.
HD Tape to Blu-ray transfer.
We are not offering Blu-Ray disc services. Below is for your reference only.
|Do you have an HD TV?|
You need to have a Digital-Ready or aks HD TV to enjoy HD movies.
|Do you have a Blu-Ray Player ?|
|I have an HD TV and a Blu-Ray Player.|
|When you have an HD TV
and a Blu-ray Player ready,
you can enjoy HD home movies.
You can also enjoy AVCHD disc on Sony or Panasonic Blu-ray player.