DV stands for Digital Video.
This standard, also called "blue book", was developed in the 90s, and carefully specifies how the data is formatted, and also how it's recorded on several media, like the mini-DV tape.
Audio will also be restored at its original quality. As audio is embedded inside the A/V frame, the repaired footage has always a good sync. (Exception: when audio is recorded in separate tracks inside .mov file, it has to be sync'ed manually).
Approximately a dozen of "profiles" are defined, the most common ones being: DV PAL and DV NTSC.
High-Definition DV, also called DVCPro HD or DVCPro100, is handled by a different codec in QuickTime despite sharing a similar architecture.
HDV is a completely different codec.
DVCPro50 is a professional variant that doubles the bit-rate. See dedicated article.
DV files (.dv suffix)
DV can usually be found in files with .dv suffix, or inside QuickTime .mov files.
dv files are made of DV frames written one after another, without any kind of structure added.
This makes corrupt DV files repairable by aggregating technique.
DV frames and profiles
DV bitstream is easy to detect and parse, because it follows a regular data pattern:
- Each frame contains exactly 120000 bytes in NTSC, 144000 in PAL.
- Each frame contains blocks of exactly 12000 bytes (10 in NTSC, 12 in PAL) that begin with 1F x7 00 with x between 0 and 9 (NTSC) or 11 (PAL).
- Furthermore, every 80 bytes exactly, the x7 bytes is repeated.
To perform a repair, it's necessary first to determine which profile is used.
If you take the 1F 07 00 pattern as reference (beginning of frame), the positions 5, 6, 7 have a value of 0x78.
Position 3 is either 3F or BF.
Position 451 can take several values.
To interpret those values, please refer to ffmpeg source code. The tables are at the end of the file dvdata.h (search for DVprofile)
DV + Audio
DV bitstream has also space reserved for a 44100Hz stereo audio track.
But video professionals usually record DV footage with external microphones: they prefer to record audio sources at 48000Hz in separate tracks rather than relying on the embedded audio track. Files recorded this way are usually QuickTime .mov containers with one video track (DV NTSC or PAL) and one or several PCM audio tracks (optional: a TimeCode track).
How to repair a corrupt DV movie
The easiest way is certainly to ask our Movie Repair Service to help you recover the lost videos.
Techniques used: Aggregating or Reindexing.
Damaged DV files are easy to repair because:
- Frames are fixed-length and contain patterns easy to detect
- DV is standardized in "profiles".
- DV encodes audio and video together inside a frame. This prevents any synchronization issue from happening, even after a repair.
The easiest way to proceed is to detect the profile, to parse the frames, and write then into a .dv file.
In some rare cases, this is not enough.
Some additional data corruption can happen, requiring investigative repairs:
- "Lost bytes", breaking the 80 bytes frequency pattern. (seen one time)
- Mispositioned blocks (several times, after a storage failure). Can be solved by De-shuffling.
- Small artifacts. Can be solved by Error-Hiding