feat(transcoder): output audio volume gain on the re-encode path#31
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Adds a per-stream audio output volume control (AudioTranscodeConfig.Volume),
applied on the re-encode path. The value follows the standard playout volume
convention: a plain linear multiplier ("2", "0.5" -> output = value x input)
or a decibel string ("+9dB", "-6dB" -> output level = input +/- dB). Both
reduce to a single linear factor via ParseAudioVolume (factor = 10^(dB/20) for
dB). Empty / "1" / "0dB" = unity gain (no change).
The gain is applied per sample on the FLTP encoder-input frame just before
encode, clamped to full scale [-1, 1] so a boost cannot wrap/distort past the
float range. Unity is a no-op (early return) so streams without a volume set
are byte-identical. Only the re-encode path is affected; audio copy /
passthrough has no decoded samples to scale.
Plumbed domain -> proto (regenerated) -> supervisor -> subprocess pipeline.
Tests: TestParseAudioVolume (linear/dB/invalid), TestApplyGain_ScalesAndClamps
and _UnityNoOp.
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What
Adds a per-stream audio output volume gain on the transcoder re-encode path (
AudioTranscodeConfig.Volume).The value follows the standard playout volume convention — two interchangeable forms that both reduce to a single linear factor:
"2","0.5"→ output = value × input"+9dB","-6dB"→ output level = input ± dB → factor =10^(dB/20)"1"/"0dB"→ unity (no change)domain.ParseAudioVolumeis the single parser (also usable for save-time validation).How
The gain is applied per sample on the FLTP encoder-input frame just before encode, clamped to full scale [-1, 1] so a boost can't wrap/distort past the float range. Unity is a no-op (early return) → streams without a volume set are byte-identical. Only the re-encode path is affected; audio copy/passthrough has no decoded samples to scale.
Plumbed
domain→proto(regenerated via protoc) →supervisor→ subprocesspipeline.Tests
TestParseAudioVolume(linear/dB/invalid/negative),TestApplyGain_ScalesAndClamps,TestApplyGain_UnityNoOp.make checkgreen (native built + raced with local libav; lint 0 issues).Notes
Already deployed to prod as
v4.4.7(dormant — no stream setsvolumeyet, so existing audio is unchanged). Volume only applies when audio is re-encoded (audio.copy=false).