How B-ROLL Picks a ProRes or DNxHR Tier Automatically

Why pick a ProRes or DNxHR tier automatically?#

B-ROLL picks the tier for you because the right ProRes or DNxHR tier depends on numbers you rarely know before a download: the source bitrate, resolution and frame rate. Choosing by hand means guessing, and guessing high fills drives with data the stream never carried.

I cut YouTube videos in DaVinci Resolve Studio on Windows 11. On my own timeline, 4K60 AV1 footage downloaded from YouTube was heavy to play back, and AV1 or VP9 downloads crashed Resolve at times. The automatic conversion in Download YouTube Videos in ProRes or DNxHR exists to fix that problem: you pick ProRes or DNx in the Format menu, and B-ROLL writes an intraframe .mov with the source resolution and frame rate.

Converting everything to the top tier would have solved playback and created a storage problem. So B-ROLL has no tier setting at all: a rule in its code decides per video. I designed the app as an editor and built it with Claude as coding help, as told in Building a YouTube Downloader with Claude as Coding Help.

How does B-ROLL scale a tier’s data rate to resolution and frame rate?#

B-ROLL stores one reference data rate per tier at 1920 x 1080 and 29.97 fps, then multiplies it by a scale factor for the video in hand. The scale factor is (width x height x fps) / (1920 x 1080 x 29.97), so it grows with pixel count and frame rate.

A 1080p30 video has a scale of 1.001, and a 2160p60 video has a scale of 8.008 (3840 x 2160 x 60 / (1920 x 1080 x 29.97)). A 720p30 video drops to 0.445. When B-ROLL cannot read the width, height or frame rate, it fills the missing value with the default written in its code: 1920 for the width, 1080 for the height, 30 for the frame rate.

The table compares B-ROLL’s internal reference rates with the rates Apple and Avid publish for the same frame size and frame rate. The DNxHR values are B-ROLL’s own figures, lower than Avid’s; Avid lists megabytes per second, converted here by multiplying by 8.

The ProRes values match the Apple ProRes white paper exactly. The DNxHR vendor column comes from Avid’s DNxHR bandwidth specifications. What each tier is for sits in ProRes Proxy vs LT vs 422 vs HQ: Which to Use and DNxHR LB vs SQ vs HQ vs HQX: Tiers Explained.

Why does B-ROLL aim for ten times the source bitrate?#

B-ROLL picks the lightest ProRes or DNxHR tier whose scaled data rate is at least 10 times the source bitrate. A one-line comment next to the rule in B-ROLL’s code gives the reason:

An intraframe codec is visually transparent to such a source at ~10x its bitrate, so any tier above that only wastes disk.

The factor works because the two kinds of codec spend bits differently. A YouTube stream stores most frames as differences from neighboring frames, while ProRes and DNxHR encode every frame on its own, as Apple’s white paper describes for ProRes. An intraframe copy therefore needs many more bits to carry the same picture, and the factor of 10 sets that margin.

The source bitrate comes from the downloaded file, not from YouTube’s label. ffmpeg measures the MKV master that yt-dlp merged: the video stream bitrate when ffmpeg reports one, otherwise the file’s overall bitrate, otherwise size divided by duration. The number on the card, explained in See the Real Bitrate and Resolution of YouTube Files, is measured on the same file but as size over duration, so the two numbers can differ slightly.

When no tier reaches 10 times the source, B-ROLL uses HQ, the heaviest tier it writes.

What happens with 10-bit sources?#

A 10-bit source exported as DNx always gets DNxHR HQX, whatever its bitrate. DNxHR LB, SQ and HQ are 8-bit, so any of them would throw away the extra bit depth, and HQX keeps it at the same data rate as HQ in Avid’s table.

B-ROLL reads the source’s bit depth with ffmpeg before converting and prints it in the log. An 8-bit source never gets HQX: 10-bit samples add nothing when the stream only holds 8 bits. If the HQX encode fails, B-ROLL falls back to DNxHR SQ at 8-bit.

ProRes skips the bit depth question. Every ProRes tier B-ROLL writes, Proxy included, is 10-bit 4:2:2, so a 10-bit source follows the normal 10x rule and keeps its depth on any tier. HDR videos are the common 10-bit case: as of September 2026, yt-dlp prefers HDR streams by default, and B-ROLL applies no tone mapping, so plan your color management around an HDR source.

Which tier do typical YouTube sources get?#

At 1080p30, B-ROLL picks ProRes 422 LT for sources over 4.5 and up to 10.2 Mbps (102 x 1.001 / 10). DNxHR SQ covers sources over 3.6 and up to 12.4 Mbps (124 x 1.001 / 10). High frame rate 4K sources can drop to Proxy or LB, because doubling the frame rate doubles every tier’s scaled rate.

The table applies the rule to illustrative sources, not measurements of specific uploads. Estimated output is the reference rate x scale, rounded; the lightest tier at or above 10 times the source wins.

Read one row to check the math. For 2160p60 at 25 Mbps, ProRes 422 Proxy scales to 360 Mbps (45 x 8.008), which already clears 250 Mbps, so Proxy wins. B-ROLL’s log prints each decision with the estimate, for example:

DNx tier auto-picked: SQ  (source ~8.0 Mbps -> output ~124 Mbps, ~1.2 GB)

The GB figure in the log line is the estimated size of the whole file for that video’s duration, not a per-minute rate. The line before the conversion also prints the source frame size and bit depth, for example source 1920x1080 8-bit.

What does the tier rule mean for disk space?#

For a typical 1080p30 upload, the tier rule writes files less than half the size of a 422 HQ export. A 1080p30 source at 8 Mbps gets ProRes 422 LT at 0.77 GB per minute (102.1 Mbps x 60 / 8 / 1,000), where 422 HQ would take 1.65 GB per minute (220.2 Mbps x 60 / 8 / 1,000).

The gap grows with length. A ten-minute 1080p30 clip at those rates is 7.7 GB in LT (0.77 x 10) against 16.5 GB in 422 HQ (1.65 x 10), and both files hold the same 10-bit 4:2:2 picture of the same stream. The heavier tiers still arrive when a source needs them: a 10-bit 2160p60 source in DNx takes 11.3 GB per minute (1,505.5 Mbps x 60 / 8 / 1,000).

Treat the log’s size as an estimate. The Apple white paper describes ProRes as a variable bit rate codec, so the real file follows the picture’s complexity rather than the target rate. Per-minute sizes for every tier sit in ProRes and DNxHR File Size per Minute (1080p and 4K). How the app reached its first build is in The First Public Release of B-ROLL, July 2026, and more posts live on the B-ROLL Blog: Releases and Behind the Scenes.