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Use FFmpeg’s loudnorm filter with the same target loudness, loudness range, and true-peak ceiling for every video—but measure each file separately. A two-pass workflow gives each file its own measurements before processing, helping keep perceived volume more consistent across a loop. The example targets below are production choices, not YouTube requirements.
Why use loudness normalization for a video loop?
Videos with different source levels can sound uneven when played consecutively. loudnorm targets integrated loudness, which is more relevant to perceived consistency than simply matching sample peaks, and can also constrain true peak. Use one shared set of target values for the batch, but use measurements from each individual file.
YouTube’s official upload encoding guidance specifies audio formats and sample rate, not a mandatory LUFS mastering target. Do not treat any particular LUFS number as a YouTube upload rule. YouTube’s upload encoding recommendations include AAC-LC, Opus, or Eclipsa Audio and a 48 kHz sample rate.
Choose target settings
The commands below use I=-16, LRA=11, and TP=-1.5 as illustrative targets. They are choices for a production workflow, not platform-mandated settings. Pick targets that suit the material and use them consistently across the loop; the filter’s documented ranges are I from -70 to -5 LUFS, LRA from 1 to 50 LU, and TP from -9 to 0 dBTP. FFmpeg’s documented defaults—I=-24, LRA=7, and TP=-2—are defaults, not YouTube recommendations. See the FFmpeg loudnorm documentation.
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Integrated loudness is the overall target, LRA is the target loudness range, and TP is the true-peak ceiling. A more restricted LRA can reduce loudness variation within a file, but the requested target LRA must not be below the source’s measured LRA for linear normalization to apply.
Two-pass workflow for each video
1. Measure the audio
Run a measurement pass for each input file. This example analyzes the first audio stream and writes no output file:
ffmpeg -i input.mp4 -map 0:a:0 -af "loudnorm=I=-16:LRA=11:TP=-1.5:print_format=json" -f null -Read the JSON report for that specific file. Record input_i, input_lra, input_tp, and input_thresh. If a video has no audio stream, this mapping will fail; decide whether to omit that file, add a suitable audio track, or handle it separately rather than applying these audio commands unchanged.
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2. Process the file using its measurements
Replace every INPUT_* token below with the corresponding measured value from the same file. The tokens are explanatory placeholders, not literal filter values.
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-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, video is stream-copied while audio is filtered and encoded as AAC. Stream-copying the video does not copy the audio: the filter must process the audio, so it is encoded again. Confirm that the input streams, output container, codec choices, and mapping suit your actual files. The optional video mapping allows an output without a video stream if the input lacks one; for ordinary video files, verify the resulting stream mapping before using the output.
Repeat both passes per file. Do not reuse the first video’s measurements for the rest. Using shared targets with file-specific measured values is what makes this a batch workflow rather than applying one file’s correction to every source.
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When linear normalization cannot be used
FFmpeg’s loudnorm supports linear and dynamic modes, but linear mode is conditional. It requires all four measured values, the requested target LRA cannot be lower than the source LRA, and the gain cannot push true peak above the target. If those constraints are not met, the filter can revert to dynamic normalization even when linear=true is requested. Inspect the filter’s reported output mode and measurements rather than assuming every file received linear processing.
Dynamic mode may be appropriate when a file’s loudness range or peak constraints prevent the requested linear adjustment. FFmpeg says dynamic mode upsamples audio to 192 kHz to detect true peaks. If you need a particular output sample rate, set it explicitly with -ar or an aresample filter and verify the output.
Single-pass alternative
FFmpeg also supports single-pass loudnorm processing for files and livestreams. It avoids a separate measurement run, which can be useful when a preliminary full-file pass is impractical. It does not provide the same workflow of measuring each complete file and then applying that file’s measurements. For a pre-recorded playlist where per-file control matters, two passes are easier to audit.
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If the input is mono and intended for stereo playback, assess the dual_mono option. FFmpeg documents it as compensation for perceptual measurement differences in that case. Check the filter documentation for its behavior and options before adding it to a batch.
Check the encoded files and YouTube playback
- Listen to transitions between neighboring videos, including quiet passages and loud sections. A matching integrated-loudness target does not make different content sound identical.
- Confirm that the output has the expected audio stream, codec, channel layout, and sample rate. YouTube’s upload guidance recommends 48 kHz and AAC-LC, Opus, or Eclipsa Audio.
- Check mono compatibility. YouTube’s audio troubleshooting guidance warns that poor mono compatibility can degrade or mute audio after stereo-to-mono conversion.
- Distinguish the processed file’s loudness from playback-side processing. YouTube says Stable volume is on by default when watching videos, where available, but it is not available for some videos and is disabled for YouTube Music and official music videos. See YouTube’s Stable volume information and its audio enhancements help page.
Troubleshooting
The filter reports dynamic mode instead of linear
Check that all four measured values were supplied from the same source file. Then compare the source LRA and true peak with the targets. If the target LRA is lower than the source LRA or the requested gain would exceed the true-peak ceiling, linear processing is not feasible under those settings; accept dynamic processing or adjust targets appropriately.
The batch still sounds inconsistent
Make sure every file uses the same target I, LRA, and TP, but its own measured values. Confirm that you are comparing the processed outputs, not a mixture of normalized and original files. Listen across transitions: source content and dynamics can still make equally normalized files feel different.
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The command fails on a file
Check that the input has an audio stream selected by -map 0:a:0, that the measured values are numeric filter values rather than the literal placeholder text, and that the output container supports the chosen streams and codecs. Review FFmpeg’s stream mapping and error output before processing the rest of the batch.
The output sample rate or channel behavior is unexpected
Set the desired sample rate explicitly with -ar or aresample if needed, then inspect the encoded output. For mono material intended for stereo playback, evaluate dual_mono and listen to the result rather than assuming channel conversion will preserve the intended sound.
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