Baseband video and audio metrics: critical in the quality control production chain.

by Andrew Martin

To extend on my previous post, technical metadata is critical in a multi stream video digitisation environment with video originating from many different formats.

Fully or semi-automated streams running with QC metrics analysing baseband video and audio signals with pre-determined thresholds is the first point in our digitisation Quality Control. We also have points of interrogation and verification such as operational video file spot checking, automated video/audio/wrapper file based checks, read/write verification on disk to disk or disk to tape, fixity checking and replication. These instances of QC in the file creation and delivery are all critical in ensuring optimum digitisation and file integrity before arrival to the customer.

The QC method I’m concentrating on in this post is using metadata information recorded on ingest to represent a quick timeline snapshot of a temporal format like video. As an example, we can determine whether macroblocking from a Digital Betacam master originated from the cassette or VTR, or whether it is a result of an error in a destination MPEG2 file by reading the metadata to see if there was a channel condition flag at the same point of visual breakup. This information is taken from the VTR channel condition and is encoded within the technical metadata XML file.

We use this information in a similar way for analogue formats like U-matic, where the Radio Frequency is recorded as metadata. If we identify an analogue based artefact such as a dropout or tape crease, we check the RF level in the metadata. Just like analogue playback monitoring, if there is a drop in RF at the same time a tape based artefact appears, there is a good chance the problem is with the original tape or VTR. (In a lot of cases the tape can be physically repaired or treated). If there is no reduction in RF at the point of artefact, then it is most probably recorded in; i.e. artefacts originating from an edit tape or VTR with physical / alignment issues. If this is the case, digital restoration is another option for removing the artefact.