# What is Transrating?

Transrating changes the bitrate of encoded audio or video, generally by re-encoding it with a different quality or rate-control target. The codec, resolution, and sampling rate may remain unchanged.

Video + audio tracks

Video processing

Playable derivative

Video processing decodes timed tracks, transforms them, and encodes a deliverable for a target player. This diagram shows video broadly, not specifically Transrating.

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## How Transrating works

A transrating job targets a new data rate while attempting to preserve the source coding family and major presentation properties. Implementations may perform a full decode and encode or use codec-specific shortcuts, but both redistribute or discard coded information to meet the new rate objective. It differs from simple repackaging because the compressed media changes. In a rendition workflow, it creates bandwidth or storage variants without necessarily changing frame dimensions.

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## Key facts

1. 1Matching the source codec and resolution does not make transrating lossless: another lossy encode can soften detail, amplify blocking, and spend bits reproducing artifacts already present.
2. 2Rate-control mode determines whether the output pursues a fixed average, a constrained peak, or a quality target, so the requested bitrate alone does not fully describe delivery behavior.
3. 3Shortcut modes that preserve the source frame structure inherit its keyframe spacing, so producing segment-aligned keyframes requires a full re-encode, which can change local bitrate demand.

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## When Transrating matters

Create lower-bitrate variants when delivery bandwidth or storage limits outweigh the cost of another encode. Aggressive reduction can introduce artifacts even when the original resolution and codec are retained.

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## Common use cases for video

These examples cover video broadly, not specifically Transrating.

* Preparing uploaded video for web, mobile, connected-TV, social, or editorial playback.
* Creating clips, thumbnails, captions, alternate aspect ratios, and adaptive renditions.
* Normalizing camera, screen-recording, and user-generated files into predictable outputs.

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## Working with video

This guidance covers video broadly, not just Transrating.

A demuxer separates tracks from the container, decoders turn compressed streams into frames or samples, and filters apply spatial or temporal changes. Encoders compress the transformed tracks before a muxer writes the chosen output container.

Video compatibility is the product of codec, container, profile, level, frame rate, color, audio, and subtitles. Validate the complete output on target devices because a playable file on one decoder may fail or look different on another.

### What you gain

* Standardized derivatives make diverse source files playable on target devices.
* A retained master can feed many resolutions, aspect ratios, codecs, and channels.
* Automated inspection and transformation make large upload volumes consistent.

### What it costs

* More efficient codecs can lower bitrate at similar quality but usually cost more compute and may have narrower support.
* Higher resolutions and frame rates preserve more detail and motion while increasing processing and delivery requirements.
* Fast encoding settings improve throughput but can produce larger files or lower quality than slower analysis.

### Before production

1. 1Inspect codec, container, dimensions, frame rate, color, audio, and subtitle tracks.
2. 2Test visual quality and playback support across the slowest and oldest target devices.
3. 3Preserve a suitable master before applying lossy, destructive, or delivery-specific changes.

[← Transmuxing](/glossary/transmuxing.md)[TS File →](/glossary/ts-file.md)

More in video

* [Thumbnail Storyboard](/glossary/thumbnail-storyboard.md)
* [Timecode](/glossary/timecode.md)
* [Transmuxing](/glossary/transmuxing.md)
* [Two-Pass Encoding](/glossary/two-pass-encoding.md)
* [Uncompressed Video](/glossary/uncompressed-video.md)
* [User-Generated Video](/glossary/user-generated-video.md)

[All 505 terms](/glossary.md)

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