punktfunk/crates/punktfunk-host/src/encode/sw.rs

//! Software H.264 encoder (openh264) — the GPU-less encode path for the Windows host (and a
//! fallback when NVENC is unavailable). Low-latency screen-content config: single-reference,
//! no B-frames (Baseline), bitrate rate-control, in-band SPS/PPS each IDR.
//! Synchronous: `submit` encodes immediately and stashes the AU for `poll` (no internal queue).
//!
//! The RGB→YUV conversion is OURS, BT.709 limited range: openh264 writes no colour description
//! into the VUI (unspecified), so decoders fall back to their default — BT.709 limited on every
//! punktfunk client — and the pixels must match that default. The crate's own `YUVBuffer`
//! converter is BT.601 (0.2578/0.5039/0.0977 + 16), which decoded-as-709 is a constant hue
//! error; that's why it is NOT used here.
// Every `unsafe` block in this file carries a `// SAFETY:` proof; enforce it (unsafe-proof program).
#![deny(clippy::undocumented_unsafe_blocks)]

use super::{EncodedFrame, Encoder};
use crate::capture::{CapturedFrame, FramePayload, PixelFormat};
use anyhow::{bail, ensure, Context, Result};
use openh264::encoder::{
    BitRate, Complexity, Encoder as Oh264, EncoderConfig, FrameRate, FrameType, IntraFramePeriod,
    Profile, RateControlMode, SpsPpsStrategy, UsageType,
};
use openh264::formats::YUVSlices;
use openh264::OpenH264API;
use std::collections::VecDeque;

pub struct OpenH264Encoder {
    enc: Oh264,
    width: u32,
    height: u32,
    fps: u32,
    src_format: PixelFormat,
    /// The converted I420 planes (our BT.709-limited CSC — see the module doc), reused across
    /// frames: full-res luma + quarter-res Cb/Cr, tightly packed (stride = width, width/2).
    y_plane: Vec<u8>,
    u_plane: Vec<u8>,
    v_plane: Vec<u8>,
    frame_idx: i64,
    force_kf: bool,
    /// One AU per submit (no lookahead), handed back FIFO by `poll`. A queue, not an `Option`:
    /// the session loop pipelines up to `capturer.pipeline_depth()` submits before polling, and a
    /// single-slot pending would silently overwrite (lose) the older AUs — including the opening
    /// IDR — and permanently skew the loop's FIFO pts pairing.
    pending: VecDeque<EncodedFrame>,
}

// openh264's Encoder holds a raw C handle (not auto-Send); it lives on the single encode thread.
// SAFETY: `OpenH264Encoder` wraps `Oh264` (openh264's `Encoder`), which holds a raw C handle to the
// openh264 `ISVCEncoder` and is not auto-`Send`; the other fields (the plane `Vec`s, scalars,
// `Option<EncodedFrame>`) are plain owned data. The session creates the encoder, calls
// `submit`/`poll`/`flush`, and drops it all on one dedicated encode thread, never sharing it by
// reference across threads, so the C handle is only ever touched from a single thread. Moving the
// whole value to that thread is therefore sound — there is no concurrent access to the handle.
unsafe impl Send for OpenH264Encoder {}

impl OpenH264Encoder {
    pub fn open(
        format: PixelFormat,
        width: u32,
        height: u32,
        fps: u32,
        bitrate_bps: u64,
    ) -> Result<Self> {
        // validate_dimensions() ran in open_video: even, non-zero, <= 4096.
        let bps: u32 = bitrate_bps.try_into().unwrap_or(u32::MAX);
        let cfg = EncoderConfig::new()
            .usage_type(UsageType::ScreenContentRealTime)
            .max_frame_rate(FrameRate::from_hz(fps.max(1) as f32))
            .rate_control_mode(RateControlMode::Bitrate)
            .bitrate(BitRate::from_bps(bps))
            .skip_frames(false)
            .intra_frame_period(IntraFramePeriod::from_num_frames(intra_period_frames(fps)))
            .sps_pps_strategy(SpsPpsStrategy::ConstantId) // SPS/PPS in-band on every IDR
            .num_threads(num_threads())
            .scene_change_detect(false) // no surprise IDRs (bitrate spikes / freeze)
            .adaptive_quantization(true)
            .complexity(Complexity::Low) // latency over BD-rate
            .profile(Profile::Baseline); // no B-frames; the VUI carries no colour description
        let api = OpenH264API::from_source(); // statically-bundled build (default `source` feature)
        let enc = Oh264::with_api_config(api, cfg).context("openh264 Encoder::with_api_config")?;
        let (w, h) = (width as usize, height as usize);
        tracing::info!(
            "openh264 software encoder: {width}x{height}@{fps} {} Mbps (Baseline, screen-content)",
            bps / 1_000_000
        );
        Ok(Self {
            enc,
            width,
            height,
            fps,
            src_format: format,
            y_plane: vec![0; w * h],
            u_plane: vec![0; (w / 2) * (h / 2)],
            v_plane: vec![0; (w / 2) * (h / 2)],
            frame_idx: 0,
            force_kf: false,
            pending: VecDeque::new(),
        })
    }

    /// Convert one packed full-range RGB frame into the I420 planes, BT.709 limited range.
    /// `bpp` is the source pixel stride; `ri`/`gi`/`bi` the channel byte offsets within a pixel.
    /// Luma per pixel; Cb/Cr from the 2×2 block's averaged RGB (the same box filter the crate's
    /// converter used, so only the matrix changed).
    fn convert_bt709(&mut self, src: &[u8], bpp: usize, ri: usize, gi: usize, bi: usize) {
        let w = self.width as usize;
        let h = self.height as usize;
        let cw = w / 2;
        for by in 0..h / 2 {
            for bx in 0..cw {
                let mut sum = (0f32, 0f32, 0f32);
                for (dy, dx) in [(0, 0), (0, 1), (1, 0), (1, 1)] {
                    let (px, py) = (bx * 2 + dx, by * 2 + dy);
                    let s = &src[(py * w + px) * bpp..];
                    let (r, g, b) = (f32::from(s[ri]), f32::from(s[gi]), f32::from(s[bi]));
                    self.y_plane[py * w + px] = luma709(r, g, b);
                    sum = (sum.0 + r, sum.1 + g, sum.2 + b);
                }
                let (cb, cr) = chroma709(sum.0 / 4.0, sum.1 / 4.0, sum.2 / 4.0);
                self.u_plane[by * cw + bx] = cb;
                self.v_plane[by * cw + bx] = cr;
            }
        }
    }
}

/// BT.709 luma coefficients (Kg = 1 − Kr − Kb).
const KR: f32 = 0.2126;
const KB: f32 = 0.0722;
const KG: f32 = 1.0 - KR - KB;

/// One full-range RGB pixel (0..=255 channels) → the BT.709 limited-range 8-bit luma code
/// (16..=235). Kept in lockstep with the client-side inverse (`pf-client-core::video::csc_rows`).
fn luma709(r: f32, g: f32, b: f32) -> u8 {
    let y = KR * r + KG * g + KB * b; // full-scale luma, 0..=255
    (16.0 + y * (219.0 / 255.0) + 0.5) as u8 // `as` saturates — no manual clamp needed
}

/// (Averaged) full-range RGB → the BT.709 limited-range Cb/Cr codes (16..=240, neutral 128).
fn chroma709(r: f32, g: f32, b: f32) -> (u8, u8) {
    let y = KR * r + KG * g + KB * b;
    let cb = 128.0 + (b - y) * (224.0 / 255.0) / (2.0 * (1.0 - KB));
    let cr = 128.0 + (r - y) * (224.0 / 255.0) / (2.0 * (1.0 - KR));
    ((cb + 0.5) as u8, (cr + 0.5) as u8)
}

impl Encoder for OpenH264Encoder {
    fn submit(&mut self, captured: &CapturedFrame) -> Result<()> {
        ensure!(
            captured.width == self.width && captured.height == self.height,
            "captured {}x{} != encoder {}x{}",
            captured.width,
            captured.height,
            self.width,
            self.height
        );
        ensure!(
            captured.format == self.src_format,
            "captured format {:?} != encoder source {:?}",
            captured.format,
            self.src_format
        );
        // Refutable once the capture backend adds `FramePayload::D3d11`; today `Cpu` is the only
        // non-Linux variant, so the pattern is (temporarily) irrefutable.
        #[allow(irrefutable_let_patterns)]
        let FramePayload::Cpu(bytes) = &captured.payload
        else {
            bail!("openh264 backend requires a CPU frame payload");
        };
        let w = self.width as usize;
        let h = self.height as usize;
        ensure!(
            bytes.len() >= w * h * self.src_format.bytes_per_pixel(),
            "captured buffer {} bytes too small for {w}x{h} {:?}",
            bytes.len(),
            self.src_format
        );

        // Source pixel stride + R/G/B byte offsets within a pixel — one converter for every
        // packed-RGB layout the capturers emit (no BGRA normalization pass needed).
        let (bpp, ri, gi, bi) = match self.src_format {
            PixelFormat::Rgb => (3, 0, 1, 2),
            PixelFormat::Bgr => (3, 2, 1, 0),
            PixelFormat::Rgba | PixelFormat::Rgbx => (4, 0, 1, 2),
            PixelFormat::Bgra | PixelFormat::Bgrx => (4, 2, 1, 0),
            // 10-bit HDR comes only from the GPU NVENC path; the software 8-bit H.264 encoder
            // can't represent it (and never receives it — the capturer pairs Rgb10a2 with NVENC).
            PixelFormat::Rgb10a2 => {
                anyhow::bail!("software H.264 encoder cannot encode 10-bit HDR (Rgb10a2)")
            }
            // NV12/P010 are GPU-resident video-processor outputs for the NVENC path; the software
            // encoder never receives them (it only gets CPU RGB frames).
            PixelFormat::Nv12 | PixelFormat::P010 | PixelFormat::Yuv444 => {
                anyhow::bail!(
                    "software encoder cannot encode YUV GPU frames (NV12/P010/YUV444 → NVENC only)"
                )
            }
        };
        self.convert_bt709(bytes, bpp, ri, gi, bi);

        if self.force_kf {
            self.enc.force_intra_frame();
            self.force_kf = false;
        }
        let slices = YUVSlices::new(
            (&self.y_plane, &self.u_plane, &self.v_plane),
            (w, h),
            (w, w / 2, w / 2),
        );
        let bs = self.enc.encode(&slices).context("openh264 encode")?;
        let mut data = Vec::new();
        bs.write_vec(&mut data); // AnnexB start codes; SPS/PPS prepended on IDR
        if !data.is_empty() {
            let keyframe = matches!(bs.frame_type(), FrameType::IDR | FrameType::I);
            let pts_ns = self.frame_idx as u64 * 1_000_000_000 / self.fps.max(1) as u64;
            self.pending.push_back(EncodedFrame {
                data,
                pts_ns,
                keyframe,
                recovery_anchor: false,
            });
        }
        self.frame_idx += 1;
        Ok(())
    }

    fn request_keyframe(&mut self) {
        self.force_kf = true;
    }

    fn poll(&mut self) -> Result<Option<EncodedFrame>> {
        Ok(self.pending.pop_front())
    }

    fn flush(&mut self) -> Result<()> {
        Ok(()) // synchronous: nothing buffered
    }
}

/// Approximate infinite-GOP: insert IDRs rarely (recovery is via `request_keyframe`/RFI). Env
/// `PUNKTFUNK_OH264_GOP` overrides (0 = encoder-auto).
fn intra_period_frames(fps: u32) -> u32 {
    if let Ok(v) = std::env::var("PUNKTFUNK_OH264_GOP") {
        if let Ok(n) = v.trim().parse::<u32>() {
            return n;
        }
    }
    fps.max(1).saturating_mul(600) // ~10 min between automatic IDRs
}

/// Encode threads. Env `PUNKTFUNK_OH264_THREADS` overrides; default 2 (latency over throughput).
fn num_threads() -> u16 {
    std::env::var("PUNKTFUNK_OH264_THREADS")
        .ok()
        .and_then(|v| v.trim().parse::<u16>().ok())
        .unwrap_or(2)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::capture::{CapturedFrame, FramePayload, PixelFormat};

    /// The BT.709 limited-range anchor points: reference white → (235,128,128), black →
    /// (16,128,128), pure red's Cr must hit the positive extreme 240 (it does exactly:
    /// 255(1−Kr)·(224/255)/(2(1−Kr)) = 112). ±1 code for float rounding.
    #[test]
    fn bt709_conversion_anchor_points() {
        assert_eq!(luma709(255.0, 255.0, 255.0), 235);
        assert_eq!(luma709(0.0, 0.0, 0.0), 16);
        assert_eq!(chroma709(255.0, 255.0, 255.0), (128, 128));
        assert_eq!(chroma709(0.0, 0.0, 0.0), (128, 128));
        let (cb, cr) = chroma709(255.0, 0.0, 0.0);
        assert_eq!(cr, 240, "pure red must reach the Cr extreme");
        assert!((101..=103).contains(&cb), "red Cb ~102, got {cb}");
        let (cb, _) = chroma709(0.0, 0.0, 255.0);
        assert_eq!(cb, 240, "pure blue must reach the Cb extreme");
    }

    /// The 601-vs-709 luma split on pure green (Kg 0.587 vs 0.7152) — guards against anyone
    /// "simplifying" the coefficients back to the crate's BT.601 converter (the hue-shift bug
    /// this module's own conversion exists to prevent).
    #[test]
    fn bt709_is_not_bt601() {
        // BT.601 green luma: 16 + 219·0.587 = 144.5; BT.709: 16 + 219·0.7152 = 172.6.
        let y = luma709(0.0, 255.0, 0.0);
        assert!((172..=174).contains(&y), "709 green luma ~173, got {y}");
    }

    /// A flat gray frame converts to neutral chroma and mid luma across every plane byte
    /// (exercises the block loop + plane sizing, not just the per-pixel math).
    #[test]
    fn converts_flat_gray_to_neutral_planes() {
        let (w, h) = (16u32, 8u32);
        let mut enc =
            OpenH264Encoder::open(PixelFormat::Bgrx, w, h, 60, 1_000_000).expect("open openh264");
        let bytes = vec![0x80u8; (w * h * 4) as usize];
        enc.convert_bt709(&bytes, 4, 2, 1, 0);
        // 16 + 128·(219/255) = 125.9 → 126.
        assert!(
            enc.y_plane.iter().all(|&y| y == 126),
            "{:?}",
            &enc.y_plane[..4]
        );
        assert!(enc.u_plane.iter().all(|&u| u == 128));
        assert!(enc.v_plane.iter().all(|&v| v == 128));
    }

    #[test]
    fn encodes_synthetic_frame_to_annexb_idr() {
        let (w, h, fps) = (1280u32, 720u32, 60u32);
        let mut enc =
            OpenH264Encoder::open(PixelFormat::Bgrx, w, h, fps, 8_000_000).expect("open openh264");
        // A flat gray BGRx frame.
        let frame = CapturedFrame {
            width: w,
            height: h,
            pts_ns: 0,
            format: PixelFormat::Bgrx,
            payload: FramePayload::Cpu(vec![0x80u8; (w * h * 4) as usize]),
        };
        enc.submit(&frame).expect("submit");
        let au = enc.poll().expect("poll").expect("an AU");
        assert!(au.keyframe, "first frame must be an IDR");
        // AnnexB start code + an SPS NAL (type 7) somewhere in the first frame.
        assert!(
            au.data.starts_with(&[0, 0, 0, 1]) || au.data.starts_with(&[0, 0, 1]),
            "expected AnnexB start code"
        );
        let has_sps = au
            .data
            .windows(5)
            .any(|w| w[0] == 0 && w[1] == 0 && w[2] == 0 && w[3] == 1 && (w[4] & 0x1f) == 7);
        assert!(has_sps, "IDR must carry an SPS NAL (type 7)");
    }
}