DV Analyzer: What Does It Analyze?
BACK TO DV ANALYZER
DV Analyzer reads through metadata within every frame of a DV video file to report on events, information, and errors. DV Analyzer information events include frames that contain jumps in recording date and time, jumps in the timecode with the DV stream, or repetition of this information (a duplicated frame). DV Analyzer also notes a list of errors such as video error concealment, audio errors, and structural inconsistencies.
The number of the frame within the video, starting from zero
Starting from 00:00:00.000. Absolute time represents the time from the beginning of the media file.
This is the timecode as documented within that frame. This information is typically written by the camera and is typically what will appear on the front of a DV deck during playback. Often this information will survive from the ingest of the source tape, through an edit, to an output; however, if the content is recompressed through rendering or a transcoding, this information is easily lost.
This could contain ‘Repeating’ if the DV Timecode is the same as the previous frame or ‘Non-sequential’ if it doesn’t follow the previous frame. This is disabled when the timecode equals ’00:00:00;00′. Timecode Info is more likely to appear in DV that has been ingested from DV tape, then edited.
Rec. Date / Time
This is the date and time as set on the recording device. A DV camera will normally document this information in every DV frame written to tape.
Rec. Date / Time Info
Similar to ‘Timecode Info’, this field states in the ‘Rec. Date / Time’ is ‘Repeating’ or ‘Non-sequential’ from the ‘Rec. Date / Time’ value of the previous frame. This happens when the recording is stopped and restarted, thus non-sequential recording date/time can be used to separate shots from an ingested DV tape.
Every block of video data with a single contains an ‘arbitrary bit’, a 4 bit value. If there is inconsistency in the arbitrary bits, the most popular one for the frame is expressed as a hexadecimal character. Typically arbitrary bit values follow a pattern of 0,1,2,3,4,5,6,7,8,9,0,A,B, then repeat (for both NTSC and PAL).
Arb bits info
Similar to ‘Timecode Info’ this value shows when the ‘Arbitrary Bit’ is ‘Repeating’ or ‘Non-sequential’ from the ‘Arbitrary Bit’ of the previous frame. A non-sequential arbitrary bit value may indicate a missing frame, an edit, or an error.
Contains an ‘S’ if the camera has noted that this frame is the first frame of a recording.
Contains an ‘E’ if the camera has noted that this frame is the last frame of a recording.
Video error concealment
DV tapes contain parity data to enable the deck to determine if data was read correctly. When video data can not be read correctly, the deck may conceal the missing information using a number of strategies. The type of concealment is documented in the output DV stream as a STA ‘STAtus of compressed macro block’ value. The STA values are noted by DVAnalyzer as a hexadecimal character
- STA = ‘A’: This block of video data is replaced by the corresponding video data of the previous frame (very common)
- STA = ‘C’: This block of video data is replaced by the corresponding video data of the next frame
- STA = ‘E’: Unspecified concealment
- STA = ‘F’: Error. This typically is represented as grey blocks on the frame.
There can be up to 1,350 STA errors per NTSC frame (1,500 in PAL). If a NTSC frame notes ‘1,350 STA errors’, then the entire frame failed to read correctly. The higher the total number of STA errors per frame, the more noticeable the concealment may be. In many case, video error concealment may not be easily detected by visual inspection.
If the DV deck fails to read audio data, it may export error codes that can be detected. They are played as dropouts, since there is no audio error concealment. Since audio data is scrambled when written to tape the audio errors will often appear to be interspersed across the duration of a frame of video.
Each frame of NTSC DV contains 90 blocks of audio data (108 in PAL). In NTSC it takes 10 passes of the deck’s head across the tape to read the data for an entire frame (12 in PAL). Each head pass reads one DIF sequence (Dseq). Often when audio fails to be read properly, it fails for the entire pass.
DVAnalyzer will provide the total number of audio block read errors (1 to 90 or 108) and detail how many occurred within each head pass (DIF sequence). If the audio errors mostly occur on odd numbered (or all even numbered) DIF sequences then the deck (or the original recording device) may have one dirty or damaged head.
DV contains many timecode values per frame (this helps enable the timecode to be viewable while the tape is shuttled). This notes when the timecodes within a frame are inconsistant. This error does not affect video or audio quality but may be indicative of other problems.
This may note structural problems with the frame such as unexpected, irregular information.
DIF incoherency means that the frame may be failing to follow basic structural expectations of DV and can cause unpredictable behaviors during playback or encoding with various hardware and software applications.
Arbitrary bit Inconsistency
This is noted when the arbitrary bits within a frame are not consistent. As noted this information is ‘arbitrary’, but can indicate issues with the frame, such as when data from two different frames is mixed into a single frame (from recording over recordings or glitchy playout).
This is noted for frames that are assigned a presentation time that is longer or shorter than the other frames (normally all DV frames are presented for same amount of time). Occasionally this is indicative or audio/video sync issues and may present a stutter during playback.