Use FFmpeg’s loudnorm filter with the same target loudness, loudness range, and true-peak ceiling for every video, but measure each file separately. For the most controlled file workflow, make a first pass to collect that file’s measurements and a second pass to normalize it. YouTube’s published upload guidance does not set a mandatory LUFS target, so treat any values in example commands as production choices—not YouTube requirements.
Why use loudness normalization for a video loop?
When a YouTube loop moves between videos, matching sample peaks alone may still leave one recording sounding much quieter or louder than another. FFmpeg’s loudnorm filter targets integrated loudness and true peak, which better addresses perceived volume consistency while limiting peaks.
For a batch, apply one common target to every file, but use measurements from that individual file. Reusing the first video’s measurements for the whole playlist can produce inconsistent results.
Choose targets without treating them as YouTube rules
The commands below use I=-16, LRA=11, and TP=-1.5 as illustrative production settings. They are not official YouTube mastering requirements. YouTube’s upload encoding recommendations cover audio formats and sample rate; they do not declare a required LUFS target.
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In FFmpeg, I is the integrated loudness target in LUFS, LRA is the loudness-range target in LU, and TP is the true-peak ceiling in dBTP. The documented ranges are -70 to -5 LUFS for I, 1 to 50 LU for LRA, and -9 to 0 dBTP for TP. FFmpeg’s defaults are I=-24, LRA=7, and TP=-2; defaults are not YouTube recommendations. Choose targets appropriate to the material and desired sound, then keep them consistent across the batch.
Normalize each video with a two-pass workflow
1. Measure the first file
Run a measurement pass for each input file. This example analyzes the first audio stream, sends the processed signal to a null output, and prints measurements as JSON:
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ffmpeg -i input.mp4 -map 0:a:0 -af "loudnorm=I=-16:LRA=11:TP=-1.5:print_format=json" -f null -From the JSON output, record input_i, input_lra, input_tp, and input_thresh. These describe this file; repeat the measurement for every video you plan to process.
2. Apply that file’s measurements
Use the common target values and the measurements recorded for this same input in the second pass. Replace each INPUT_* value with the corresponding number from the measurement output; the labels shown below are explanatory placeholders, not literal filter values.
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ffmpeg -i input.mp4 -map 0:v? -map 0:a:0
-af "loudnorm=I=-16:LRA=11:TP=-1.5:measured_I=INPUT_I:measured_LRA=INPUT_LRA:measured_TP=INPUT_TP:measured_thresh=INPUT_THRESH:linear=true"
-c:v copy -c:a aac output.mp4Here, -c:v copy stream-copies the existing video without re-encoding it. The audio is different: because it is filtered, FFmpeg must process and encode it, here as AAC. Check that the input has the streams you expect and that the output container and selected audio codec suit your files. If there is no audio stream, the -map 0:a:0 mapping will fail and the file needs a separate handling path.
3. Repeat the passes for the rest of the playlist
For every video, run its own measurement pass, then substitute its own measurements into the second-pass command. Keep I, LRA, and TP fixed across the files. That combination—shared targets, file-specific measurements—is the essential batch rule.
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When linear normalization falls back to dynamic mode
The second command requests linear=true, but linear normalization is conditional. FFmpeg requires all four measured values for this mode. It may revert to dynamic normalization if the requested target loudness, target loudness range, and true-peak constraint cannot be met together. In particular, the target LRA must not be lower than the source’s measured LRA, and the required gain must not push true peak above the selected ceiling.
Do not assume the output is necessarily in linear mode just because the command requested it. Review FFmpeg’s output and, if needed, adjust the target choices or accept dynamic processing. The filter can change dynamics to satisfy constraints; it cannot guarantee that every source will retain the same dynamics while meeting every target.
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Single-pass option and audio details
When a single pass is practical
FFmpeg documents loudnorm for both single-pass processing and double-pass file processing. A single pass can be useful when a preliminary full-file measurement is impractical, but it does not follow the same measure-then-apply workflow with full-file, file-specific measurements. For a playlist where you want consistent processing decisions per file, the two-pass method gives you explicit measurements to work with.
Sample rate and mono audio
FFmpeg says dynamic mode upsamples audio to 192 kHz for true-peak detection. If you need a specific output sample rate, set it explicitly with -ar or an aresample filter, and verify the resulting file. For mono input intended for stereo playback, assess the dual_mono option: FFmpeg documents it as compensation for perceptual measurement differences in that case.
YouTube recommends AAC-LC, Opus, or Eclipsa Audio and a 48 kHz sample rate in its upload encoding guidance. Its audio troubleshooting guidance also warns that poor mono compatibility can degrade or mute audio after stereo-to-mono conversion. Listen to representative sections after processing, particularly if the source mixes or channels behave differently.
What YouTube playback processing does—and does not—mean
Normalizing a file before upload is not the same as YouTube adjusting playback volume. YouTube says Stable volume is on by default when watching videos where the feature is available, but it is unavailable for some videos and disabled for YouTube Music and official music videos. Playback-side volume handling is not a substitute for preparing consistent source files, nor does it establish a required mastering target.
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- The command reports a mapping error: Check that the input contains the stream selected by
-map 0:a:0. A video without audio needs a different mapping or should be skipped by the batch process. - The output audio sounds unchanged or too different: Confirm that the filter ran, that the measured values came from this input, and that the output audio was encoded rather than copied. Listen to several sections; a numeric loudness target cannot ensure every passage has identical subjective loudness.
- FFmpeg does not stay in linear mode: Review the source measurements and target constraints. The target LRA cannot be below measured source LRA for linear mode, and the gain must respect the true-peak limit. Adjust targets where appropriate or allow dynamic mode.
- Audio is clipped, weak, or otherwise degraded after upload: Check the true-peak target, output codec and sample rate, channel mapping, and mono compatibility. Compare the processed local file with playback on YouTube; playback-side processing can differ from the file itself.
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