User`s manual

INTRODUCTION

Thank you for your V1 purchase. The V1 is a random access digital video disk recorder that uses

magnetic drives (hard drives) as a recording medium.

To record video on a hard drive it should be digitized which means that the analog video

information must be converted to a digital data stream. Every NTSC video frame contains 525

lines that have 858 pixels each, however, only 480 lines with 720 pixels each are used to hold

picture information.

The table below indicates the bit rate standard definition (SD) and high definition (HD) video

without the use of compression.

Resolution 8 bit encoding 8 bit encoding 10 bit encoding 10 bit encoding

Mbits/sec MBytes/sec Mbits/sec MBytes/sec

SD 720x480 (NTSC) 166 20.7 207 25.89

SD 720x576 (PAL) 166 20.7 207 25.89

HD 1920x1080x60Hz 995 124.4 1244 155.5

HD 1920x1080x59.94Hz 994 124.3 1243 155.4

HD 1920x1080x50Hz 829 103.7 1037 129.6

HD 1920x1080x30P 995 124.4 1244 155.5

HD 1920x1080x25P 829 103.7 1037 129.6

HD 1920x1080x24P 796 99.5 995 124.4

HD 1280x720x60P 934 116.7 1167 145.9

HD 1280x720x50P* 778 97.3 973 121.6

*Not implemented.

The V1 line of products includes uncompressed video recorders (8 and 10 bit encoding) and

compressed video recorders (8 bit encoding), the trade off is between storage requirement and

video quality.

V1 Uncompressed

The V1-U series records the video directly on the hard drive without the use of compression.

(V1-U & V1-Ux2 for standard definition video and the V1-UHD for HDTV video).

V1 Compressed ( DCT vs MPEG2 )

Doremi’s V1 product line includes models that use DCT compression (the V1, V1m, V1d, and

V1x2) and MPEG2 compression (V1-MP2).

DCT (Discrete Cosine Transform) consists of compressing every field of video and saving the

data on the drive. MPEG2 is a more advanced compression technique that yields a better transfer

rate than DCT for the same video quality. MPEG2 will yield better quality when recording on

DVD-RAM drives and larger servers can be built with MPEG2 units.

The CBS algorithm

The V1 uses a constant block size (CBS) algorithm. With traditional compression algorithms,

depending on video complexity, the size of each compression field can vary thus requiring

maintaining a list to indicate the start of each field on the drive. With CBS all fields have the

same maximum size. Consequently, CBS does not require maintaining a list indicating the start

of each field because they are all the same size. This results in a more reliable disk recorder with

faster video access and frame accurate recording.