music_player/src/decoder.rs

use std::{
	io::Cursor,
};

use anyhow::{
	anyhow,
	Result,
};

use byteorder::{
	LittleEndian,
	ReadBytesExt,
};

// This crate flitters between being very convenient and being a type labyrinth.

use ffmpeg_next::{
	decoder::Audio as DecodeContext,
	format::context::Input as DemuxContext,
	software::resampling::Context as ResamplingContext,
	util::{
		channel_layout::ChannelLayout,
		format::sample::{
			self,
			Sample,
		},
		frame::Audio as FfAudioFrame,
	},
};

pub const SAMPLE_RATE: u32 = 48000;

pub struct AudioFrame {
	frame: FfAudioFrame,
}

impl AudioFrame {
	pub fn data (&self) -> &[u8] {
		// Hard-coded because I'm only support f32 interleaved stereo
		&self.frame.data (0) [0..self.frame.samples () * 4 * 2]
	}
	
	pub fn rate (&self) -> u32 {
		self.frame.rate ()
	}
	
	pub fn samples (&self) -> usize {
		self.frame.samples ()
	}
}

impl From <FfAudioFrame> for AudioFrame {
	fn from (frame: FfAudioFrame) -> Self {
		Self {
			frame,
		}
	}
}

#[derive (Default)]
pub struct PcmBuffers {
	buffers: Vec <Vec <f32>>,
	
	// Always points into the first buffer, if any
	consumer_cursor: usize,
}

impl PcmBuffers {
	pub fn samples_available (&self) -> usize {
		self.buffers.iter ().map (|b| b.len ()).sum::<usize> () - self.consumer_cursor
	}
	
	#[warn(unused_must_use)]
	pub fn consume_exact (&mut self, data: &mut [f32]) -> bool {
		if data.len () > self.samples_available () {
			return false;
		}
		
		for x in data {
			if self.consumer_cursor >= self.buffers [0].len () {
				self.buffers.remove (0);
				self.consumer_cursor = 0;
			}
			
			*x = self.buffers [0][self.consumer_cursor];
			self.consumer_cursor += 1;
		}
		
		true
	}
	
	pub fn produce (&mut self, new_buffer: Vec <f32>) {
		self.buffers.push (new_buffer);
	}
	
	pub fn produce_bytes (&mut self, new_buffer: &[u8]) {
		let mut b = vec! [0.0f32; new_buffer.len () / 4];
		let mut rdr = Cursor::new (new_buffer);
		
		// Pointless memcpy. I can get rid of it later by changing PcmBuffers'
		// internal format
		rdr.read_f32_into::<LittleEndian> (&mut b).unwrap ();
		
		self.produce (b);
	}
}

pub struct Decoder {
	pub input_ctx: DemuxContext,
	pub decoder: DecodeContext,
	pub resampler: ResamplingContext,
	
	best_stream_idx: usize,
	dummy_frame: Option <FfAudioFrame>,
}

impl Decoder {
	pub fn new (filename: &str) -> Result <Self> {
		let input_ctx = ffmpeg_next::format::input (&filename)?;
		let stream = input_ctx
		.streams ()
		.best (ffmpeg_next::media::Type::Audio)
		.ok_or_else (|| anyhow! ("can't find good audio stream"))?;
		let best_stream_idx = stream.index ();
		
		let decoder = stream.codec ().decoder ().audio ()?;
		let resampler = decoder.resampler (
			Sample::F32 (sample::Type::Packed),
			ChannelLayout::STEREO,
			48000,
		)?;
		
		Ok (Self {
			input_ctx,
			decoder,
			resampler,
			
			best_stream_idx,
			dummy_frame: None,
		})
	}
	
	fn new_frame () -> FfAudioFrame {
		let mut x = FfAudioFrame::empty ();
		x.set_channel_layout (ChannelLayout::STEREO);
		x.set_format (Sample::F32 (sample::Type::Packed));
		x
	}
	
	pub fn next (&mut self) -> Result <Option <AudioFrame>> {
		Ok (if let Some (frame) = self.pump ()? {
			assert_eq! (frame.rate (), 48000);
			assert! (frame.samples () > 0);
			
			Some (frame)
		}
		else {
			None
		})
	}
	
	fn pump (&mut self) -> Result <Option <AudioFrame>> {
		loop {
			match self.pump_resampler ()? {
				Some (x) => {
					// tracing::trace! ("Pumped resampler");
					return Ok (Some (x));
				},
				None => (),
			}
			
			match self.pump_decoder ()? {
				Some (x) => {
					// tracing::trace! ("Pumped decoder");
					return Ok (Some (x));
				},
				None => (),
			}
			
			if self.pump_demuxer ()? {
				// tracing::trace! ("Pumped demuxer");
				continue;
			}
			else {
				break;
			}
		}
		
		Ok (None)
	}
	
	pub fn pump_resampler (&mut self) -> Result <Option <AudioFrame>> {
		let frame_src = match self.dummy_frame.as_ref () {
			None => return Ok (None),
			Some (x) => x,
		};
		
		let mut frame_resampled = Self::new_frame ();
		
		let _rc = self.resampler.run (&frame_src, &mut frame_resampled)?;
		// dbg! (&frame_resampled, rc);
		
		Ok (if frame_resampled.samples () > 0 {
			// tracing::trace! ("Pulled from resampler FIFO");
			Some (frame_resampled.into ())
		}
		else {
			None
		})
	}
	
	pub fn pump_decoder (&mut self) -> Result <Option <AudioFrame>> {
		let mut frame_src = FfAudioFrame::empty ();
		if let Err (_) = self.decoder.receive_frame (&mut frame_src) {
			return Ok (None);
		};
		
		if self.dummy_frame.is_none () {
			let mut dummy_frame = FfAudioFrame::new (
				frame_src.format (),
				0,
				frame_src.channel_layout (),
			);
			dummy_frame.set_rate (frame_src.rate ());
			self.dummy_frame = Some (dummy_frame);
		}
		
		let nb_output_samples = frame_src.samples ();
		
		let mut frame_resampled = FfAudioFrame::new (
			Sample::F32 (sample::Type::Packed),
			nb_output_samples,
			ChannelLayout::STEREO
		);
		
		self.resampler.run (&frame_src, &mut frame_resampled)?;
		Ok (Some (frame_resampled.into ()))
	}
	
	pub fn pump_demuxer (&mut self) -> Result <bool> {
		while let Some ((stream, packet)) = self.input_ctx.packets ().next () {
			if stream.index () == self.best_stream_idx {
				// tracing::trace! ("demuxed packet");
				self.decoder.send_packet (&packet)?;
				return Ok (true);
			}
		}
		
		Ok (false)
	}
}

#[cfg (test)]
mod test {
	use super::*;
	
	#[test]
	fn pcm_buffer () {
		let mut x = PcmBuffers::default ();
		
		x.produce (vec! [0.0, 1.0, 2.0, 3.0]);
		x.produce (vec! [4.0, 5.0, 6.0, 7.0]);
		
		let mut data = vec! [0.0; 3];
		
		assert! (x.consume_exact (&mut data));
		assert_eq! (&data, &[0.0, 1.0, 2.0]);
		
		assert! (x.consume_exact (&mut data));
		assert_eq! (&data, &[3.0, 4.0, 5.0]);
	}
}