NearVid

2026-10-10

Steamworks’ own trailer page has no length or file-size limit — but it does set resolution, bitrate, and codec requirements

Search for "Steam trailer requirements" and most of what comes back is a third-party guide quoting a length or file-size cap — and they disagree with each other. Steamworks' own trailer documentation settles that part quickly: it states a resolution, a frame rate, a bitrate, a container list, and a codec preference — but no maximum length and no maximum file size, anywhere on the page. Here's exactly what Valve's own page does require, the two failure causes its own FAQ names directly, and how NearVid's lossless Trim and Convert to MP4 line up against each of them.

What Steamworks' own page actually specifies

The documentation describes the trailer you should upload in one passage: "The trailer should be the highest resolution that you have, up to 1920 x 1080 resolution, high bit rate (5,000+ Kbps) and in .mov, .wmv, or .mp4 container files." Unpacked line by line, per the same page:

The same page adds one detail easy to miss: "Please note that audio will be filtered down to regular stereo when we transcode the videos" — whatever channel layout the source carries, Steam's own transcode step reduces it to stereo regardless.

What Steamworks' own FAQ says actually breaks a trailer upload

The page's FAQ section answers "What do I do if my trailer processing ended with an error?" with two specific, ranked causes, quoted directly: "The most common reason for a trailer to fail is the resolution of the video. Please ensure you use a common resolution such as 1920x1080 or 1280x720 to avoid any downstream processing issues." and, second: "Another common issue is an unsupported audio sample rate (please use 44Khz or 48Khz)." Both are about matching the source file to an expectation, not about trimming it shorter or compressing it smaller — nothing in the FAQ names length or size as a failure cause at all.

No length or size limit stated — which isn't the same as "upload the raw capture"

It's tempting to read "no size limit" as "nothing to prepare." In practice, a raw OBS or capture- card recording of a full play session is rarely the 60–90 second highlight a trailer actually needs, and it's rarely already in one of the three named containers at a clean H.264/AAC pairing — long sessions commonly land as NVENC HEVC inside an .mkv, or VP9 inside a .webm, neither of which matches Steamworks' stated preference. Getting from "the raw capture" to "the clip Steamworks' own page describes" is still two separate jobs: cut it down, then get the codec/container right.

Raw capture to Steamworks' Trailers tab Two separate jobs, in order: cut it down, then get the codec/container right Raw capture Any length, any container/codec → NearVid Trim Lossless stream-copy codec/container unchanged → NearVid Convert H.264 Baseline + AAC-LC, into .mp4 → Store Page Admin Trailers tab Two gaps neither NearVid step closes: Bitrate — High preset caps at 4 Mbps; Steamworks' own page recommends "5,000+ Kbps" Frame rate / resolution — neither step changes these; source must already be 30/29.97 or 60/59.94 fps and at or under 1920x1080, per Steamworks' own FAQ on why trailers fail Trim and Convert each do one real step correctly — neither claims to check the rest of Steamworks' spec for you.
NearVid's two operations cover the cut and the codec/container; Steamworks' own stated bitrate recommendation and its FAQ's resolution/sample-rate failure causes are things to confirm on the source footage separately.

Where NearVid's lossless Trim fits — before any re-encode happens

packages/near-video-engine/engine.js lists the containers its Trim operation recognizes directly in code: CONTAINER_EXTS includes 'mp4', 'mov', 'm4v', 'webm', 'mkv', 'avi', 'ts', 'flv', 'wmv', '3gp', 'ogv', 'mpg', 'mpeg' — covering all three containers Steamworks' page names (.mov, .wmv, .mp4) plus the .mkv and .webm a raw capture is likely to actually be in. The same file's header comment states what Trim does to any of them: "trim() can stream-copy ANY input container/codec losslessly (no encoder invoked at all)." Cutting the full session down to the 60–90 second highlight at this stage costs nothing in quality and nothing in re-encode time, because no encoder runs — whatever codec the capture already used stays exactly as recorded, container unchanged, before Convert to MP4 ever touches it.

Where NearVid's Convert to MP4 fits — and where it falls short of Steamworks' own recommendation

Once the clip is cut, packages/near-video-engine/mp4-engine.js re-encodes it to the exact pairing Steamworks' page prefers: the module sets H264_BASELINE_CODEC_STRING = 'avc1.42001f' (profile 0x42/Baseline, level 0x1f/3.1) and AAC_LC_CODEC_STRING = 'mp4a.40.2', muxed into an MP4 — one of the three containers named, with the exact codec pair Steamworks' page calls preferred. convertToMp4() sets no width or height override, so whatever resolution the source already carries — up to and including 1920x1080 — passes through unchanged, and it pins no audio sample rate either, so the output inherits whatever rate the source track used; most capture software already records at 44.1kHz or 48kHz, the exact two rates Steamworks' own FAQ names as acceptable.

Where this stops short: apps/nearvid/src/workspace.js defines MP4_QUALITY_BITRATE = { high: 4_000_000, medium: 2_000_000, low: 800_000 } — the High preset is a flat 4 megabits per second, under Steamworks' own stated "high bit rate (5,000+ Kbps)" figure. NearVid's own code doesn't offer anything above that preset today, so a trailer where every last bit of Steamworks' recommended bitrate floor matters needs a different encoder for that one setting. And VIDEO_INPUT_FORMATS in the same file lists MP4, QTFF/MOV, Matroska, WebM, and MPEG-TS — not WMV — so a raw capture that happens to already sit in a .wmv container can still be trimmed losslessly (it's in CONTAINER_EXTS above) but can't be fed into Convert to MP4 directly; in practice this rarely matters, since MP4 is itself one of Steamworks' three accepted containers.

What this doesn't do

NearVid doesn't upload to Steam, doesn't call Steamworks' API, and doesn't know whether a given file will actually process successfully once it reaches Valve's own pipeline — that verdict happens entirely on Steam's side, after upload. It doesn't check or change frame rate, so a 24fps or oddly variable-framerate capture stays exactly as recorded; matching Steamworks' stated "30/29.97 or 60/59.94 fps" is on the source footage, not something either NearVid operation touches. It doesn't exceed its own 4Mbps High preset, and it doesn't resample audio to a specific rate. What it does do, entirely before any upload: cut the full session down losslessly, and re-encode that clip to the H.264 Baseline + AAC-LC pairing Steamworks' own page prefers, inside an MP4 — both finished on-device.

The honest summary

Steamworks' own trailer documentation names a resolution ceiling, a frame rate, a bitrate target, three accepted containers, and a preferred codec pair — but states no maximum length and no maximum file size anywhere on the page, and its own FAQ names resolution mismatches and unsupported audio sample rates, not file size, as the two common reasons a trailer fails to process. NearVid's lossless Trim can cut a full raw session down to the highlight clip without touching the source's codec or container at all, and its Convert to MP4 can re-encode that clip into the exact H.264 Baseline + AAC-LC + MP4 combination Steamworks' page calls preferred — both finished on-device, before the file ever reaches Valve's own upload pipeline. The one place NearVid's own numbers don't quite reach Steamworks' own recommendation is bitrate: 4Mbps at the High preset against a stated "5,000+ Kbps" floor, named here rather than smoothed over.