Broadcast

Applications 128TestVid clips provide a complete range of demanding stress tests for encoders, video servers, transcoders or other equipment, featuring SD, HD and 2K, all the way up to 4K, as well as various web, streaming, or other low resolution formats. Confirm the signal path and test/evaluate new or upgraded software or devices. Fully searchable documentation makes it easy to target and test specific functionality.

 

Application - Broadcast

4K 1284K 1284K 128hD 128VVQ 128

The ever-changing broadcast environment requires the most up to date tools for setup, integration and quality assurance. This is especially useful where new or emerging formats, equipment or setups are being evaluated or adopted.

Broadcasters can use TestVid clips in testing or evaluation of:

  • Video encoders (hardware and software)
  • Video servers
  • Transcoders (hardware and software)
  • Format converters (frame rates/resolutions/bit depths/other, e.g. 2-D to 3-D stereoscopic)
  • Set-top boxes

TestVid clips can be used to test the following functionality:

Function

Description of possible tests

Comparison of vendor's equipment

Direct comparisons on different encoders / video servers, comparing functionality, speed, efficiency and quality* of encoding, for example to help decide which vendor's equipment / which model to buy

Evaluation of technical approach

To check out new approaches, bit-rates etc. to determine if encoding with particular parameters provides desired / adequate quality* levels

Comprehensive stress testing

Provide a comprehensive test set of video which includes worst case and 'difficult' sequences, to check that an encoder / other equipment does not slow down and lose a/v sync  with particular video features

Efficiency testing

Test the ability of equipment to efficiently compress / handle a wide variety of video:

  • to determine what are the 'sweet spots' and the problem areas / video types in efficiency terms
  • if required encoding / transmission bit-rates can be met on all types of video, while retaining a desired minimum quality*

Functional testing

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:

  • the versions required for web and mobile applications (perhaps producing / outputting them concurrently with SD / HD)
  • versions which may be required in future, e.g. 1080p60 and 3-D stereoscopic

Regression testing

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 inefficiencies.)

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 PSNR is well-known to not have good correlation with visual perception in many instances.

Some vendors of visual quality measurement equipment are:

Vendor

Equipment

Notes

Omnitek

PQA

  

PixelMetrix

DVStation

Uses PixelMetrix' QMM quality measure

Rohde & Schwarz

DVQ; DVQM

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

Tektronix

PQA500, PQA300

Researched to correlate well with visual perception

Footnote

In the end, when evaluating video quality in a broadcast environment 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 quality of new services to pay more for it?