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|
use media::{AudioSamples, Decoder};
use time::MediaTime;
use crate::Error;
use crate::clips::AudibleClip;
pub const MASTER_LIMITER_THRESHOLD_DB: f64 = -1.0;
pub const MASTER_LIMITER_RATIO: f64 = 20.0;
pub const MASTER_LIMITER_ATTACK_SECONDS: f64 = 0.001;
pub const MASTER_LIMITER_RELEASE_SECONDS: f64 = 0.12;
pub const MASTER_OUTPUT_HEADROOM: f64 = 0.98;
pub const MASTER_OUTPUT_HEADROOM_F32: f32 = 0.98;
fn decode_clip_source(clip: &AudibleClip, source_start: f64, source_end: f64) -> Option<AudioSamples> {
let start = MediaTime::from_seconds_f64(source_start.max(0.0))?;
let end = MediaTime::from_seconds_f64(source_end.max(0.0))?;
if end <= start {
return None;
}
let mut decoder = Decoder::open(&clip.path).ok()?;
let stream = decoder.info().audio_streams.first().cloned()?;
decoder.decode_audio_range(stream.index, start, end).ok()
}
fn mix_clip(
clip: &AudibleClip,
range_start_seconds: f64,
out_frames: usize,
sample_rate: u32,
channel_count: usize,
output: &mut [f32],
) {
let clip_start_seconds = clip.start_time.to_seconds_f64();
let clip_end_seconds = clip_start_seconds + clip.duration.to_seconds_f64();
let rate = clip.effective_rate();
let trim_start_seconds = clip.trim_start.to_seconds_f64();
let rate_f64 = f64::from(sample_rate);
let first_frame = ((clip_start_seconds - range_start_seconds) * rate_f64)
.ceil()
.max(0.0) as usize;
let last_frame = (((clip_end_seconds - range_start_seconds) * rate_f64)
.ceil()
.max(0.0) as usize)
.min(out_frames);
if last_frame <= first_frame {
return;
}
let source_start = trim_start_seconds
+ (first_frame as f64 / rate_f64 + range_start_seconds - clip_start_seconds) * rate;
let source_end = trim_start_seconds
+ (last_frame as f64 / rate_f64 + range_start_seconds - clip_start_seconds) * rate;
let Some(decoded) = decode_clip_source(clip, source_start, source_end) else {
return;
};
let decoded_channels = decoded.channels as usize;
let decoded_frames = decoded.samples.len() / decoded_channels;
let decoded_rate = f64::from(decoded.sample_rate);
let static_gain = clip.static_gain() as f32;
let animated_volume = clip.has_animated_volume();
for frame in first_frame..last_frame {
let clip_time = frame as f64 / rate_f64 + range_start_seconds - clip_start_seconds;
let source_time = trim_start_seconds + clip_time * rate;
let source_position = (source_time - source_start) * decoded_rate;
if source_position >= decoded_frames as f64 {
break;
}
let source_position = source_position.max(0.0);
let lower = source_position.floor() as usize;
let upper = (lower + 1).min(decoded_frames.saturating_sub(1));
let fraction = (source_position - lower as f64) as f32;
let gain = if animated_volume {
clip.gain_at(MediaTime::from_seconds_f64(clip_time).unwrap_or(MediaTime::ZERO)) as f32
} else {
static_gain
};
for channel in 0..channel_count {
let source_channel = channel.min(decoded_channels - 1);
let a = decoded.samples[lower * decoded_channels + source_channel];
let b = decoded.samples[upper * decoded_channels + source_channel];
output[frame * channel_count + channel] +=
(a * (1.0 - fraction) + b * fraction) * gain;
}
}
}
pub fn mix_range(
clips: &[AudibleClip],
range: (MediaTime, MediaTime),
sample_rate: u32,
channels: u32,
) -> Result<Vec<f32>, Error> {
if range.1 <= range.0 {
return Err(Error::InvalidTimeRange);
}
if sample_rate == 0 {
return Err(Error::InvalidSampleRate);
}
if channels == 0 {
return Err(Error::InvalidChannelCount);
}
for clip in clips {
if clip.requires_maintain_pitch()
&& clip.end_time() > range.0
&& clip.start_time < range.1
{
return Err(Error::MaintainPitchUnsupported {
element_id: clip.element_id.clone(),
rate: clip.effective_rate(),
});
}
}
let range_seconds = (range.1 - range.0).to_seconds_f64();
let out_frames = (range_seconds * f64::from(sample_rate)).ceil() as usize;
let channel_count = channels as usize;
let mut output = vec![0.0_f32; out_frames * channel_count];
let range_start_seconds = range.0.to_seconds_f64();
for clip in clips {
mix_clip(
clip,
range_start_seconds,
out_frames,
sample_rate,
channel_count,
&mut output,
);
}
Ok(output)
}
pub fn apply_mastering(samples: &mut [f32], channels: usize, sample_rate: u32) {
let peak = samples.iter().fold(0.0_f32, |peak, s| peak.max(s.abs()));
if f64::from(peak) <= MASTER_OUTPUT_HEADROOM {
return;
}
let attack_coeff =
(-1.0 / (MASTER_LIMITER_ATTACK_SECONDS * f64::from(sample_rate))).exp();
let release_coeff =
(-1.0 / (MASTER_LIMITER_RELEASE_SECONDS * f64::from(sample_rate))).exp();
let mut envelope_db = 0.0_f64;
for frame in samples.chunks_mut(channels) {
let level = frame.iter().fold(0.0_f32, |level, s| level.max(s.abs()));
let level_db = 20.0 * f64::from(level.max(1e-6)).log10();
let over = level_db - MASTER_LIMITER_THRESHOLD_DB;
let target_db = if over > 0.0 {
-over * (1.0 - 1.0 / MASTER_LIMITER_RATIO)
} else {
0.0
};
let coeff = if target_db < envelope_db {
attack_coeff
} else {
release_coeff
};
envelope_db = target_db + (envelope_db - target_db) * coeff;
let gain = 10_f64.powf(envelope_db / 20.0) * MASTER_OUTPUT_HEADROOM;
for sample in frame.iter_mut() {
*sample = (f64::from(*sample) * gain) as f32;
}
}
for sample in samples.iter_mut() {
*sample = sample.clamp(-MASTER_OUTPUT_HEADROOM_F32, MASTER_OUTPUT_HEADROOM_F32);
}
}
pub fn render_export_buffer(
clips: &[AudibleClip],
total_duration: MediaTime,
sample_rate: u32,
channels: u32,
) -> Result<Vec<f32>, Error> {
if clips.is_empty() || total_duration <= MediaTime::ZERO {
return Ok(Vec::new());
}
let mut buffer = mix_range(clips, (MediaTime::ZERO, total_duration), sample_rate, channels)?;
apply_mastering(&mut buffer, channels as usize, sample_rate);
Ok(buffer)
}
|
