FAQs
Moving Media are specialists in video encoding and transcoding services. We have compiled the following information to hopefully assist information hungry video owners in finding out more about digital video.
What is compression?
Compression is a means of reducing the amount of data required to deliver a piece of digital video. Compression is necessary as the native bitrates of broadcast video or DVD are much higher that can be transmitted in real-time over the public internet.
Compressing video comes at a cost: as you compress video you lose clarity of image and can introduce some picture degeneration known as ‘blockiness’. Faults in a video sequence that are as a result of compression are often referred to as artefacts or aliasing.
You can read more about video compression here.
You can read more about video compression here.
What are the most common online video formats?
There are many to choose from. Your choice of video format will be driven by how you wish to deliver your video – for example, by stream or download – both having advantages. However, you may require the security a streamed file provides.
For streaming we see Flash and Windows Media as being the most common formats with other emerging technologies such as Microsoft Silverlight becoming more available.
For download we often deal with MP4 (H.264 and other variants depending on the target device).
In recent years advances in video encoding have been made by a number of different companies and engineering groups. Whereas in the earlier part of the decade MPEG I, MPEG II, AVI and Windows Media were common video formats, formats such as MP4, Flash and WM9 are most widely used as they are next generation technologies and more efficient in terms of their treatment of video data.
For streaming purposes, many CDNs (Content Delivery Networks such as Akamai, Limelight) or online video Platforms such as Brightcove use Flash encoding for streaming video. However, they can also support other downloadable formats such as MP4 or more recently Microsoft Silverlight.
For digital master files we often use hi-resolution MPEG II profiles such as MPEG50i, MXF or uncompressed AVI files.
For streaming we see Flash and Windows Media as being the most common formats with other emerging technologies such as Microsoft Silverlight becoming more available.
For download we often deal with MP4 (H.264 and other variants depending on the target device).
In recent years advances in video encoding have been made by a number of different companies and engineering groups. Whereas in the earlier part of the decade MPEG I, MPEG II, AVI and Windows Media were common video formats, formats such as MP4, Flash and WM9 are most widely used as they are next generation technologies and more efficient in terms of their treatment of video data.
For streaming purposes, many CDNs (Content Delivery Networks such as Akamai, Limelight) or online video Platforms such as Brightcove use Flash encoding for streaming video. However, they can also support other downloadable formats such as MP4 or more recently Microsoft Silverlight.
For digital master files we often use hi-resolution MPEG II profiles such as MPEG50i, MXF or uncompressed AVI files.
What is de-interlacing and why does it matter for online video?
Digital video viewed over the internet using LCD or similar monitors requires that video be progressive scanned or de-interlaced. De-interlacing refers to the process of converting a video signal from interlaced broadcast format to progressive scan digital format. De-interlacing is a complicated process in itself and can also introduce problems into a digital video file. An ineffective de-interlacing system can introduce motion and edge artefacts into a video signal, while correct de-interlacing will allow the video to be seen as it would look on a standard television monitor when displayed on an LCD or computer monitor.
Interlacing is a broadcasting technique used to improve the picture quality of a video transmission without consuming any extra bandwidth. This system reduces transmitted bandwidth to half by displaying each video frame by two interlacing (interwoven) fields. One field carries the even video lines and the other the odd lines.
Interlaced video is designed to be captured, transmitted or stored and displayed in the same interlaced format. Because modern computer video displays are progressive scan systems, interlaced video will have visible artifacts when it is displayed on computer systems.
To minimise the artefacts caused by interlaced video display on a progressive scan monitor, a process called de-interlacing can be utilised. The quality of a video signal that has been converted through de-interlacing to a progressive signal can vary depending on the quality of the de-interlacing system used.
An interlaced video when viewed on a progressive scan monitor such as a computer or LCD screen will appear to have horizontal lines which are slightly misaligned; this effect will make straight vertical lines appear jagged within a frame. The effect is seen most with faster moving images.
Interlacing is a broadcasting technique used to improve the picture quality of a video transmission without consuming any extra bandwidth. This system reduces transmitted bandwidth to half by displaying each video frame by two interlacing (interwoven) fields. One field carries the even video lines and the other the odd lines.
Interlaced video is designed to be captured, transmitted or stored and displayed in the same interlaced format. Because modern computer video displays are progressive scan systems, interlaced video will have visible artifacts when it is displayed on computer systems.
To minimise the artefacts caused by interlaced video display on a progressive scan monitor, a process called de-interlacing can be utilised. The quality of a video signal that has been converted through de-interlacing to a progressive signal can vary depending on the quality of the de-interlacing system used.
An interlaced video when viewed on a progressive scan monitor such as a computer or LCD screen will appear to have horizontal lines which are slightly misaligned; this effect will make straight vertical lines appear jagged within a frame. The effect is seen most with faster moving images.
What common problems can occur with digital video?
The quality of digital video at any given bit rate is largely derived from the quality of the encoding scheme, system and process used to deliver the digital video file.
The lower the bit rate of a digital video file the higher the level of degeneration one should expect to see.
Where an issue exists in a digital video file as a result of compression that should not be there or was not present in the original file it is referred to as an artefact or as aliasing.
A blocking artefact is the most common video compression artefact experienced with low bitrate video encoding. This undesirable artefact derives its name from the fact that it results from the processing of portions of video images in blocks, e.g., 8×8 blocks of pixels.
Blocking artefacts are seen more in footage which contains fast moving images or panning shots. Blocking can also occur in images where a high level of tone detail and range of colour exists. The compression of this type of material often causes posterisation of colour; this is seen as blocks of different shades of a colour within an image.
The lower the bit rate of a digital video file the higher the level of degeneration one should expect to see.
Where an issue exists in a digital video file as a result of compression that should not be there or was not present in the original file it is referred to as an artefact or as aliasing.
A blocking artefact is the most common video compression artefact experienced with low bitrate video encoding. This undesirable artefact derives its name from the fact that it results from the processing of portions of video images in blocks, e.g., 8×8 blocks of pixels.
Blocking artefacts are seen more in footage which contains fast moving images or panning shots. Blocking can also occur in images where a high level of tone detail and range of colour exists. The compression of this type of material often causes posterisation of colour; this is seen as blocks of different shades of a colour within an image.
How long does it take to have a video encoded?
Using the correct technology video encoding can be a real-time process – using multiple parallel systems a company such as Moving Media can digitise and encode large volumes of video in a relatively short period of time.
I have video tape, I need to encode it. What are the key bits of information I need?
1. Target format – find out the technical spec for video for the particular platform you wish to deliver video to. This information could include:
Call our studios in Los Angeles or Dublin if you would like to discuss any of this information – we are always happy assist companies in defining their technical requirements for digital video.
- Codec – for eg MP4, Flash, Windows Media
- Bitrate – for eg. 700kbps or 2Mbps
- Screen size – 360 x 480
- Audio – Mono or Stereo, bitrate?
- Other considerations could include frame rate or encoder profile
- Will you require a ‘mezzanine file?’ (a high res master file used to create lower res versions as requirements arise)
- Source format – DVD, DV, Digibeta, SP….
- Duration of Content
- Does the content require editing? For example are there slates and ad brakes on the tape that will need to be removed?
- Does the tape have multiple items that will need to be separated into individual digital video files?
Call our studios in Los Angeles or Dublin if you would like to discuss any of this information – we are always happy assist companies in defining their technical requirements for digital video.
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