Video Encoding | DVDTECH

Definition

The video needs to be compressed to fit onto a DVD, CD or intranet. A compressed format (MPEG-2) is used for DVD to reduce the total data storage to manageable levels whilst maintaining high quality levels.

Why Use DVDTECH

DVDTECH uses world-class video encoders. The BIG difference is quality, and knowledge. World-class quality whilst maximising your DVD capacity.

The first difference is each tape that you submit is inspected by quality control to ensure that it meets the quality standards for use as a DVD source. You are then contacted if necessary for decisions based on our recommendations. This saves time and money for both parties.

Unlike most authoring facilities, we use a total of three different encoders, that pre-process video ensuring that it maximises the quality of the input of the video, BEFORE it gets to the encoder. We ensure that we use the right encoder for your Job.

Then knowledge plays an important part, after the encoder has up to 2 separate passes at the source tape, the encoder recommends certain actions. Experience is used to determine the best possible action, given the job requirements.

Finally a skilled compressionist, to ensure that the art is put back into the science of video encoding, views the entire stream, and checks it for DVD compliance. This blend of the best hardware encoder and knowledge ensures the highest quality result, which at this point you can view if required.

So you can be confident that the same video encoding process that was used on the latest Hollywood blockbuster is used on your corporate DVD title.

We accept the following tape formats.

Both NTSC and PAL masters acceptable
Digital Betacam
Betacam IMX
Betacam SX
Betacam SP
Mini DV
DVCAM

Have a digital file format already? Uncompressed Quicktime, AVI and TGA files can also be used by prior arrangement.

We can output the following file formats on DVD, CD, or upload them via ftp to your intranet site.

Format	Player Download
MPEG-2 (CBR, VBR)
MPEG-1 (CBR)	PC Mac	Windows Media Player Quicktime Player
QuickTime		Quicktime Player
AVI		Windows Media Player
Real		RealPlayer

More Information

Learn More

The DVD-Video format requires that video data be compressed in either the MPEG-1 or MPEG-2 formats. A compressed format is used to reduce the total data storage requirements for the video elements to a manageable level. “Broadcast” or “CCIR-601” quality video requires approximately 21 Mbytes/second of storage space and throughput. This means that a DVD-5 disc (4.37 GBytes) could hold only about 3.7 minutes of uncompressed, or raw, video.

MPEG-1 compressed video has a resolution of 352x240 pixels per frame and a frame rate of 30 non-interlaced frames per second (for NTSC countries). Most MPEG-1 files are compressed at a constant bit rate of approximately 1.4 Mbits/Second, which is consistent with the recommendations of the Video-CD standard. MPEG-1 compressed video provides quality roughly comparable to VHS tape, and if higher data rates are used the quality can approach SVHS tape. A standard DVD-5 (4.3 Gb) disc can hold approximately 7.5 hours of MPEG-1 video compressed at a standard Video-CD rates. Video CD is an extremely popular format in Asia, but has never caught on in either the US or Europe since both areas had large installed bases of VHS players when Video CD first became available. Many DVD-Video players support the Video CD format, and some of the first titles released for DVD players were actually Video CD discs with MPEG-1 data. Despite Video CD’s popularity in Asia, the vast majority of DVD-Video titles have been published using MPEG-2 compressed video in order to provide better overall video quality.

MPEG-2 compressed video has a resolution of 720x480 pixels per frame and a frame rate of 30 frames per second for NTSC countries, or a resolution of 720x576 pixels per frame and a frame rate of 25 frames per second for PAL countries. MPEG-2 files can be created using a constant-bit-rate encoding process or a variable-bit-rate encoding process. If a constant-bit-rate encoding process is used a bit rate of approximately 6 Mbits/Sec or higher is required to provide compressed video that is as good as the original CCIR-601 source. If a variable-bit-rate encoding process is used, an average bit rate of less than 4.0 Mbits/Sec can be used to generate compressed video that looks nearly as good as the original CCIR-601 source.

CCIR-601 component video is fed into a series of pre-filters and temporal and spatial scaling equipment to generate a high quality component digital video signal. The digital signal is then converted from RGB component format into the Y/Cr/Cb component format. Each frame of digital video is compressed using a Discrete Cosine Transform algorithm that removes redundant data (Intraframe Compression). Next each frame is compared to previous and future frames to eliminate redundant data between frames (Interframe Compression). Finally the compressed video data is formatted to comply with the MPEG-2 file format standards.

There are steps required to generate an MPEG-2 compressed digital video file.

An MPEG-2 bit stream is composed of a sequence of Slices, Pictures, and Group Of Pictures. An MPEG-2 Picture corresponds to a single full resolution frame, with two Slices that correspond to each field of the interlaced frame. There are three types of encoded frames in MPEG-2. An I frame includes all of the information required to fully reconstruct the source frame. Subsequent Pictures within the Group Of Pictures will be P or B frames. P and B frames are predictive frames, which means they only store the changes from the previous or next frame. A Group Of Pictures is a sequence of compressed frames that starts with a Picture that is an MPEG-2 I frame. The DVD-Video format book requires that the MPEG-2 compressed digital video stream include no more than 18 Pictures in each Group Of Pictures. The number of Pictures in a Group Of Pictures is also called the GOP size. The DVD-Video format book also requires that the MPEG-2 video data be multiplexed with any associated audio, sub-picture, still image, and control data.

When variable bit rate encoding is used, the actual number of bits dedicated to the MPEG encoding process is varied depending on the content of the video stream. If the video content is a scene of someone speaking, with a relatively static background, then fewer bits can be used to accurately describe the static scene. If the video content is a high action scene with both foreground and background motion, or a scene with a lot of fine detail, a higher bit rate must be used to avoid introducing digital artifacts into the compressed digital video file.

Lossy digital video compression techniques, including MPEG-1 and MPEG-2, can create digital artifacts during the compression process. Digital artifacts can include Colour Distortion, Colour Bleeding, Hue and Tint Degradation, Motion Degradation, Noise Pumping, Frame Duplication, Frame Drops, Aliasing, Blocking, Fringing, and Ringing. The most common digital artifacts generated in MPEG compressed video streams are Blocking, Colour Bleeding, and Fringing. Blocking is the presence of 8 x 8 pixel pattern blocks in the compressed video stream that were not part of the original source. Blocking is caused by the use of the Discrete Cosine Transform algorithm, which operates on an 8 x 8 pixel block. Colour Bleeding occurs when colours from one area of a frame migrate into neighbouring areas of the same frame. Colour Bleeding occurs more often with “hot” colours such as red, yellow or orange.

Ringing is the presence of a blurring, or out of focus effect around the edges of an object that is moving from frame to frame. Ringing occurs more often when there is a large amount of motion between frames of the video.

Digital video artifacts can be eliminated using a variety of techniques. Most artifacts can be removed by increasing the average bit rate used to compress the content. Filtering the input video stream to eliminate high frequency noise is also a common technique for reducing artifacts. Artifacts that occur in only a single frame of the digital video can be removed by touching-up the pixels that have been distorted, although this is a very labour-intensive process.