Interlaced and broadcast exports in Video by Zaweba

Television still asks for files that most home editors never touch. A broadcaster or playout house may want an interlaced MXF at a fixed bit rate, or an OP-Atom file that drops straight into an edit suite, and a web export will simply be sent back. Video by Zaweba has a set of export targets made for that kind of delivery, and it keeps them in the same Export window you already use for everyday files.

This article covers what those targets are, when you need them, and how to avoid the small slips that get a file rejected.

What the broadcast targets are

There are two formats aimed squarely at broadcast. The first is XDCAM HD422 at 1080i, written as an .mxf file at 50 Mbit/s. That is a long-standing house format for many channels and news operations, and if a delivery sheet mentions XDCAM HD422 or 50 megabit 1080i, this is the one to pick. The second is DNxHR HQ in OP-Atom form, the layout where picture and sound sit in separate MXF files, which is what some finishing and edit systems expect to receive.

Alongside those, the app lets you set the field order for any export written as MPEG-2, XDCAM, ProRes, DNxHR or uncompressed. You can choose upper field first or lower field first. Those are the formats where interlacing still matters, so the choice lives where you need it and stays out of the way elsewhere.

Getting the field order right

Interlaced video draws each frame as two fields, one carrying the odd lines and one the even lines, shown one after the other. If a file says it starts with the upper field but the receiving system plays the lower one first, movement judders and edges comb. It is one of the most common reasons a technically correct file still looks wrong on air.

The answer is nearly always written on the delivery specification, so read it before you export rather than guessing. If the spec says upper field first, set that; if it says lower field first, set that. When you are handing over a file for a colleague's system and nobody has told you, ask. It costs a short message and saves a second export.

Keep in mind that field order is a property of the file you write. The edit itself happens on the same frame-accurate timeline as any other project, so you can cut, grade and mix exactly as you normally would and only make the interlacing decision at the end.

A sensible routine for a broadcast delivery

Start from the delivery sheet and set the project to match its frame rate before you cut much, so you are not converting late in the day. Edit as usual. When you reach the Export window, choose the target the sheet names, set the field order, and check the sound settings the sheet asks for. Video by Zaweba also has a broadcast-safe limiter and burned-in timecode among its wider export options, and many channels want one or the other, so it is worth reading the sheet once more for those lines.

Once the file is written, play it back through, ideally on a screen that shows interlaced material properly. Look at fast motion and fine horizontal detail, which is where a field order mistake shows first.

Mistakes that send files back

The usual problems are simple. A progressive web preset gets used out of habit. The field order is left at whatever the last export used. The project frame rate does not match the channel's. Each of these is quick to fix and annoying to discover after upload, so a short check before pressing Export pays for itself.

It also helps to save your broadcast settings as a preset of your own once you have them right. The app lets you keep presets with favourites, so the next delivery to the same place is a single choice rather than a fresh set of decisions.

Where it fits

Most people using Video by Zaweba will export MP4 for the web and never think about fields. The broadcast targets are there for the day a job needs them, offline and with no account, in the same window and with the same timeline behind them. If your work goes to television even occasionally, it is worth making one test file early so you know the route before a deadline arrives.