Legal levels, and the check before you export

What "legal" means

Broadcast signals have defined limits. In 8-bit video range, black is 16 and white is 235, with the space above and below reserved for overshoot in the analogue chain. Values outside that band are illegal, and a broadcaster's automated quality control will reject a file that contains them.

For web delivery nothing is rejected, which is why most people never encounter this. It still matters, for two reasons: clipped values at either end are detail you have destroyed, and a file that exceeds the range interacts badly with the range conversions of the previous lesson.

Reading it on the waveform

Set your waveform scope to show values in the broadcast range, and the limits appear as lines.

• Anything flat against the top line is clipped highlights. A flat horizontal line at the top of the trace means a region of the image has gone to pure white with no detail in it.
• Anything flat against the bottom is crushed shadows.
• A trace that extends beyond either line is illegal.

A small amount of clipping is normal and often intentional — a light source in frame, a reflection off chrome. A wide flat plateau at the top means a face or a sky has lost its detail.

Chroma can be illegal too

Less obvious: a colour can be within the luminance limits and still be out of range, because the combination of luminance and chroma produces an RGB value outside the band.

Heavily saturated reds are the usual culprit. On a vectorscope, colours extending past the target boxes at the corners are the warning.

The fix is a soft clip or a broadcast-safe limiter, which rolls off the extremes rather than cutting them. Resolve has both a soft clip control on the primaries and a Broadcast Safe setting in Project Settings with selectable tolerances. Turn it on for broadcast delivery; leave it off for web, where it costs you saturation you are allowed to have.

The quality-control pass

Before any export goes out, run this list. It takes the length of the film plus ten minutes and it catches the errors that are expensive to discover after delivery.

Watch the whole thing, at full screen, without touching anything. Not scrubbing. The whole thing. This is the only step that catches most problems, and it is the one people skip when they are late.

Then check, specifically:

• Black frames. A single frame of black between two clips, usually from a gap on the timeline. Zoom out and look for gaps; in Resolve, a gap shows as a break in the track.
• Audio dropouts. A track muted, a clip with no audio, a gap in the room tone bed.
• Sync at the end. Drift is invisible at the start and obvious at minute eight. Check the last scene specifically.
• Spelling in every title and super. Names especially. Getting somebody's name wrong is the error people remember.
• The caption track, read end to end against the audio.
• Levels: integrated loudness and true peak, measured, from the earlier block.
• The first and last frame. Not black, and the last frame holds for long enough to not feel cut off.
• Placeholder material. Temporary music, a scratch voice-over, a LOGO HERE card, a watermarked stock clip. This is the mistake that reaches a client most often.
• The export's actual properties. Run ffprobe on the finished file and confirm resolution, frame rate and duration are what you intended. It takes five seconds and it catches the project that was set up wrong three weeks ago.

Watch the export, not the timeline

The important discipline: this check is performed on the exported file, played in a normal player, not on the timeline in your editor.

The timeline shows you a rendered preview that may differ from the file in range handling, colour tagging and audio routing. Several classes of error exist only in the export. Watching the timeline and calling it checked is how a washed-out file ships.

A written checklist

Keep it as a text file in your template project and tick it every time. Not because the steps are hard, but because the failure mode is doing this at 1am on the delivery day, from memory, with three of them missed.

Today

Export thirty seconds of something, open it in VLC, and compare it against the timeline. Then run ffprobe on it and read the resolution and frame rate. That is the habit.