TestVid clips are ideal for use when developing or optimizing a video codec as used in a semiconductor, software encoder, set-top box, video camera, multimedia device, broadcast hardware encoder or any similar product. Test all aspects of codec response and behaviour with licensed high quality media.
Application - Codec Development
Appropriate uses of TestVid clips in codec development applications would be in development of:
- semiconductors, particularly as may be used as part of the simulation process prior to tape-out
- hardware or software encoders, transcoders and format converters, using custom hardware, GPUs or general purpose processors, or a combination
- set-top boxes
- video cameras
- other multimedia devices
- hardware devices which take uncompressed video as input
The functions that Tvids could be used for with the above equipment are:
Description of uses
Comprehensive stress testing
Provide a comprehensive test set of video which includes worst case and 'difficult' sequences, to check that the encoder does not slow down and lose a/v sync with particular video features
Test the ability of equipment to efficiently compress / handle a wide variety of video:
Testing an equipment's ability to input and/or generate not only SD (NTSC/PAL) and 'normal' HD such as 720p or 1080i, but also to efficiently and reliably produce:
Comparison with competitor's equipment
Direct comparisons with similar equipment from competitors (or perhaps earlier models of vendor's own equipment) , comparing functionality, speed, efficiency and quality* of encoding, for example to determine strong and weak points versus competitors' products
Evaluation of technical approach
To check out new approaches, bit-rates etc. to determine if encoding with particular parameters provides desired / adequate quality* levels
Check out new versions of software on equipment and compare with previous versions encoding / processing speed, efficiency and quality*.
I.e. answer the question is the latest software 'upgrade' really an upgrade or are there particular types of video where there is a problem
* Quality testing: some possible means of quality evaluation are listed below.
How to generate an SDI / ASI / DVI / HDMI real-time stream
Use the TestVid Player included in the TestVid Tools for real time HD-SDI/SDI/DVI/HDMI playback. If required you can use TestVid Reactor to convert the file to various high quality industry standard broadcast, production and scientific file formats.
All video servers, many hardware encoders and a large proportion of other equipment have internal hard disks and Gig-E Ethernet interfaces. This allows the TestVid clips to be directly copied over the broadcaster's Ethernet network onto the hard disk, and output from there.
Where it is required to produce an output stream as an input to other equipment, this can be done relatively straightforwardly, using:
- a high performance PC / Mac
- with high speed RAID hard disks
- with an appropriate I/O board, e.g. from AJA, Blackmagic Design or Bluefish444
- and software such as TestVid Player to control moving the video from disk onto the I/O interface
Quality testing of broadcast video
Note: this is only intended as a very brief introduction and list of some of the possible equipment that might be used for video quality testing / evaluation: this subject is already extensively covered by many books, research papers and occupies many people involved in research and development of new techniques.
(This assumes that the video is technically correct, i.e. that the video quality is not affected by incorrect encoding / break-up / appearance of green macroblocks etc., although of course there can be macroblock effects / blockiness due to insufficient bit-rate or encoder inefficiences.)
Some basic ideas
There are two types of quality testing that can be done:
- quantitative, i.e. taking measurements
- qualitative, i.e. evaluation by people
Many types of measurements can be done, such PSNR (peak signal-to-noise ratio): the hardest part with all these measurements is coming up with a repeatable measurement scheme that correlates well with human visual perception.
The last part of the sentence also helps to explain why visual quality testing is so hard:
- everyone has a different perception of video quality
- perception of video quality varies enormously with content (e.g. humans see detail far less and accept blurriness far more in fast-moving objects)
- many other parameters affect perceived visual quality, such: as viewing environment (looking at a window on a computer screen is very different to viewing a 50" plasma screen at home which is very different to a broadcast viewing suite); what expectations people have of picture quality (e.g. movies versus TV news coverage); and extraneous factors, including such things as audio quality.
Equipment to evaluate video quality
There are many software packages which include straightforward technical measurements such as PSNR: this is a starting point but is well-known to not have good correlation with visual perception in many instances.
Some vendors of visual quality measurement equipment are:
Uses PixelMetrix' QMM quality measure
Rohde & Schwarz
Uses Rohde & Schwarz own measurement (developed with others)
- various -
Using Sarnoff JND
'JND'='Just-Noticeable Difference' that is a just-noticeable video difference between the uncompressed video source and encoded compressed video. Sarnoff Corporation developed a means of evaluating visual quality; other companies now incorporate JND into their equipment
Researched to correlate well with visual perception
In the end, when evaluating video quality the questions may come down to looking at the video with an expert eye and making a judgment:
- are the customers likely to notice any visual quality / complain about it / lose customers because of it
- will customers be sufficiently excited by the video quality of the product you offer when compared to competitors, that they will buy your product over others