DVswitch/ DV format

There are many variants of the DV format, officially specified in:

A large part of each of these standards defines tape formats, but we are only concerned with the DV interchange format (DIF) which uses the same basic elements for all variants.

Other sources of information:

All bits and bytes not defined are reserved and should be set to 1.

Frame format

Each video frame is compressed separately (except in HDV). The video, the corresponding audio and metadata are divided into 80-byte blocks which are multiplexed in the following 150-block (12 KB) sequence:

This sequence is repeated between 10 and 48 times depending on the DV variant and video standard used, for a frame size of between 120 and 576 KB. DVswitch only supports the 25 Mbit (video) variants of DV, which have 10 (NTSC) or 12 (PAL) sequences per frame.

Block format

Each block begins with a 3-byte header identifying its type and position in the frame, to aid resynchronisation:

The format of the remaining 77 bytes varies between types.

Header block

Subcode blocks

Each block contains 6 of the following subcode structures followed by 29 reserved bytes.

VAUX blocks

These contain 15 packs followed by 2 reserved bytes.

Audio blocks

These contain 1 pack followed by 36 16-bit PCM samples or 48 12-bit companded PCM samples. The samples are not stored in original order but are shuffled, perhaps to aid audio playback from a limited number of blocks during fast-forward or rewind.

Video blocks

Video compression is complex and will not be described here. Metadata is stored separately in the VAUX blocks.

Pack format

Packs are 5 bytes long, with the first byte being a type code.

Time code (TC)

This is based on LTC but without the sync word. The user bits may be encoded in a binary group pack.

Appears as pack 3 in each subcode block, and also as pack 5 in subcode blocks in the first half of each frame.

Binary group (BG)

Appears as pack 4 in subcode blocks in the first half of each frame.

AAUX source (AS)

Appears in audio block 3 (sequence block 54) in even sequences and audio block 0 (sequence block 6) in odd sequences.

AAUX source control (ASC)

Appears in audio block 4 (sequence block 70) in even sequences and audio block 1 (sequence block 22) in odd sequences.

Audio/video recording date

Audio/video recording time

VAUX source (VS)

Appears as pack 9 in VAUX block 2 (sequence block 5) in even sequences and pack 0 in VAUX block 0 (sequence block 3) in odd sequences.

VAUX source control (VSC)

Appears as pack 10 in VAUX block 2 (sequence block 5) in even sequences and pack 1 in VAUX block 0 (sequence block 3) in odd sequences.

No info pack

This appears where information is missing or in the subcode and VAUX blocks where no pack is assigned.