diff --git a/src/lib.rs b/src/lib.rs
index ae49749..9f69b84 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -13,6 +13,7 @@ pub mod metainfo;
 pub mod newpipe;
 pub mod page;
 pub mod service;
+pub mod stream;
 pub mod youtube;
 
 pub use downloader::{Downloader, Request, Response};
diff --git a/src/stream/audio.rs b/src/stream/audio.rs
new file mode 100644
index 0000000..079e806
--- /dev/null
+++ b/src/stream/audio.rs
@@ -0,0 +1,20 @@
+// AudioStream — one DASH or progressive audio variant.
+
+use crate::stream::DeliveryMethod;
+use crate::youtube::itag::MediaFormat;
+
+#[derive(Clone, Debug)]
+pub struct AudioStream {
+    pub itag: u32,
+    pub url: String,
+    pub format: MediaFormat,
+    pub delivery: DeliveryMethod,
+    pub average_bitrate_kbps: Option<u32>,
+    pub codec: Option<String>,
+    pub content_length_bytes: Option<i64>,
+    pub audio_track_id: Option<String>,
+    pub audio_track_name: Option<String>,
+    pub audio_locale: Option<String>,
+    pub is_descriptive: bool,
+    pub itag_url_format: Option<String>,
+}
diff --git a/src/stream/delivery.rs b/src/stream/delivery.rs
new file mode 100644
index 0000000..d078e73
--- /dev/null
+++ b/src/stream/delivery.rs
@@ -0,0 +1,14 @@
+// DeliveryMethod — how a stream is fetched.
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
+pub enum DeliveryMethod {
+    /// Direct progressive download (single HTTP GET, byte ranges).
+    Progressive,
+    /// DASH manifest URL — adaptive, segment-by-segment.
+    Dash,
+    /// HLS manifest URL — adaptive, mostly for live.
+    Hls,
+    /// Torrent magnet / .torrent URL. Not used by YT; included for parity
+    /// with NPE for other services we may add later.
+    Torrent,
+}
diff --git a/src/stream/mod.rs b/src/stream/mod.rs
new file mode 100644
index 0000000..9ee9b28
--- /dev/null
+++ b/src/stream/mod.rs
@@ -0,0 +1,89 @@
+// Stream value types — mirrors NPE's stream/ package.
+//
+// Shapes lifted from NPE so the Rust port produces the same data
+// callers see today. Codec strings ("avc1.4d401f", "vp9.2") are kept as
+// opaque strings — they come from YT's response mimeType and we don't
+// classify them ourselves.
+
+pub mod audio;
+pub mod delivery;
+pub mod subtitles;
+pub mod video;
+
+pub use audio::AudioStream;
+pub use delivery::DeliveryMethod;
+pub use subtitles::SubtitlesStream;
+pub use video::VideoStream;
+
+use crate::image::ImageSet;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
+pub enum StreamType {
+    None,
+    VideoStream,
+    AudioStream,
+    LiveStream,
+    AudioLiveStream,
+    VideoLiveStream,
+    PostLiveStream,
+    PostLiveAudioStream,
+}
+
+/// Per-video metadata + format lists. Mirrors NPE StreamInfo.java.
+#[derive(Clone, Debug, Default)]
+pub struct StreamInfo {
+    pub service_id: u32,
+    pub url: String,
+    pub video_id: String,
+    pub stream_type: Option<StreamType>,
+
+    pub name: String,
+    pub description: String,
+    pub duration_seconds: i64,
+    pub view_count: i64,
+    pub like_count: i64,
+    pub dislike_count: i64,
+    pub upload_date_iso: Option<String>,
+    pub thumbnails: ImageSet,
+
+    pub uploader_name: String,
+    pub uploader_url: String,
+    pub uploader_id: String,
+    pub uploader_avatars: ImageSet,
+    pub uploader_subscriber_count: i64,
+    pub uploader_verified: bool,
+
+    pub audio_streams: Vec<AudioStream>,
+    pub video_streams: Vec<VideoStream>,
+    pub video_only_streams: Vec<VideoStream>,
+    pub subtitles: Vec<SubtitlesStream>,
+
+    pub dash_manifest_url: Option<String>,
+    pub hls_manifest_url: Option<String>,
+
+    pub related_streams: Vec<StreamInfoItem>,
+    pub tags: Vec<String>,
+    pub category: String,
+}
+
+/// Shorter "card" used in search results, channel video lists, playlists.
+/// Mirrors NPE StreamInfoItem.java.
+#[derive(Clone, Debug, Default)]
+pub struct StreamInfoItem {
+    pub service_id: u32,
+    pub url: String,
+    pub name: String,
+    pub thumbnails: ImageSet,
+
+    pub uploader_name: String,
+    pub uploader_url: String,
+    pub uploader_id: String,
+    pub uploader_verified: bool,
+
+    pub duration_seconds: i64,
+    pub view_count: i64,
+    pub upload_date_relative: String,
+
+    pub stream_type: Option<StreamType>,
+    pub short_description: String,
+}
diff --git a/src/stream/subtitles.rs b/src/stream/subtitles.rs
new file mode 100644
index 0000000..4a432bc
--- /dev/null
+++ b/src/stream/subtitles.rs
@@ -0,0 +1,11 @@
+// SubtitlesStream — closed-caption / subtitle track.
+
+#[derive(Clone, Debug)]
+pub struct SubtitlesStream {
+    pub url: String,
+    pub language_code: String,
+    pub name: String,
+    pub is_auto_generated: bool,
+    /// MIME type (`application/ttml+xml`, `text/vtt`, `application/x-subrip`, etc.)
+    pub mime: String,
+}
diff --git a/src/stream/video.rs b/src/stream/video.rs
new file mode 100644
index 0000000..f8475af
--- /dev/null
+++ b/src/stream/video.rs
@@ -0,0 +1,22 @@
+// VideoStream — one DASH or progressive video variant. `video_only=true`
+// means it's an adaptive video-only track that has to be paired with an
+// AudioStream by the consumer (ExoPlayer handles this via DASH).
+
+use crate::stream::DeliveryMethod;
+use crate::youtube::itag::MediaFormat;
+
+#[derive(Clone, Debug)]
+pub struct VideoStream {
+    pub itag: u32,
+    pub url: String,
+    pub format: MediaFormat,
+    pub delivery: DeliveryMethod,
+    pub resolution: String,
+    pub fps: u32,
+    pub bandwidth: Option<u32>,
+    pub codec: Option<String>,
+    pub content_length_bytes: Option<i64>,
+    pub width: Option<u32>,
+    pub height: Option<u32>,
+    pub video_only: bool,
+}
diff --git a/src/youtube/mod.rs b/src/youtube/mod.rs
index 33cb4ec..12c98c6 100644
--- a/src/youtube/mod.rs
+++ b/src/youtube/mod.rs
@@ -8,4 +8,5 @@ pub mod constants;
 pub mod itag;
 pub mod js;
 pub mod parsing;
+pub mod stream_helper;
 
diff --git a/src/youtube/parsing.rs b/src/youtube/parsing.rs
index 65b9bf4..a461766 100644
--- a/src/youtube/parsing.rs
+++ b/src/youtube/parsing.rs
@@ -16,7 +16,6 @@ use regex::Regex;
 use serde_json::Value;
 
 use crate::downloader::request::Request;
-use crate::downloader::Downloader;
 use crate::exceptions::ParsingError;
 use crate::localization::{ContentCountry, Localization};
 use crate::newpipe::NewPipe;
diff --git a/src/youtube/stream_helper.rs b/src/youtube/stream_helper.rs
new file mode 100644
index 0000000..5525dd6
--- /dev/null
+++ b/src/youtube/stream_helper.rs
@@ -0,0 +1,261 @@
+// YoutubeStreamHelper — 5 per-client /player request helpers.
+// Mirrors NPE services/youtube/YoutubeStreamHelper.java.
+//
+// Each helper builds the InnerTube envelope + the per-endpoint payload
+// (videoId, cpn, contentCheckOk, racyCheckOk, playbackContext, optional
+// serviceIntegrityDimensions for poToken), POSTs to the right URL with
+// the right headers, returns the parsed JSON.
+
+use serde_json::{json, Map, Value};
+
+use crate::downloader::request::Request;
+use crate::exceptions::{NetworkError, ParsingError};
+use crate::localization::{ContentCountry, Localization};
+use crate::newpipe::NewPipe;
+use crate::youtube::client_request::{build_envelope, InnertubeClientRequestInfo};
+use crate::youtube::constants::*;
+use crate::youtube::parsing::{
+    android_user_agent, ios_user_agent, mobile_post_headers, youtube_post_headers,
+};
+
+/// Builds a 12-char alphanumeric `cpn` (content playback nonce). NPE uses
+/// a custom alphabet; we mirror it. NOT cryptographically random — just
+/// shaped to look like YT's own format. Per-client cpn, so we keep it as
+/// a free helper.
+pub fn generate_content_playback_nonce() -> String {
+    use std::time::{SystemTime, UNIX_EPOCH};
+    const ALPHABET: &[u8] =
+        b"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";
+    let mut seed = SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_nanos() as u64)
+        .unwrap_or(0);
+    let mut out = String::with_capacity(16);
+    for _ in 0..16 {
+        seed = seed.wrapping_mul(6364136223846793005).wrapping_add(1442695040888963407);
+        out.push(ALPHABET[(seed.rotate_right(7) as usize) % ALPHABET.len()] as char);
+    }
+    out
+}
+
+/// Common body fields every /player call needs.
+fn add_player_body_fields(body: &mut Map<String, Value>, video_id: &str, cpn: &str) {
+    body.insert("videoId".into(), Value::String(video_id.into()));
+    body.insert("cpn".into(), Value::String(cpn.into()));
+    body.insert("contentCheckOk".into(), Value::Bool(true));
+    body.insert("racyCheckOk".into(), Value::Bool(true));
+}
+
+fn add_playback_context(body: &mut Map<String, Value>, signature_timestamp: i32, referer: &str) {
+    body.insert(
+        "playbackContext".into(),
+        json!({
+            "contentPlaybackContext": {
+                "signatureTimestamp": signature_timestamp,
+                "referer": referer,
+            }
+        }),
+    );
+}
+
+fn add_service_integrity_dimensions(body: &mut Map<String, Value>, po_token: &str) {
+    body.insert(
+        "serviceIntegrityDimensions".into(),
+        json!({ "poToken": po_token }),
+    );
+}
+
+fn envelope_to_body(envelope: Value) -> Map<String, Value> {
+    match envelope {
+        Value::Object(map) => map,
+        _ => Map::new(),
+    }
+}
+
+/// WEB-client metadata-only /player call. Per audit Track A §4.4 — used
+/// for microformat + thumbnails only; never used as a stream URL source.
+pub fn get_web_metadata_player_response(
+    video_id: &str,
+    localization: &Localization,
+    content_country: &ContentCountry,
+    signature_timestamp: i32,
+) -> Result<Value, ExtractionError> {
+    let info = InnertubeClientRequestInfo::of_web_client();
+    let env = build_envelope(&info, localization, content_country, None);
+    let mut body = envelope_to_body(env);
+    add_player_body_fields(&mut body, video_id, &generate_content_playback_nonce());
+    add_playback_context(&mut body, signature_timestamp, "https://www.youtube.com");
+    let url = format!(
+        "{YOUTUBEI_V1_URL}player{DISABLE_PRETTY_PRINT_PARAM}&$fields=microformat,videoDetails.thumbnail.thumbnails,videoDetails.videoId"
+    );
+    post_youtube(&url, &Value::Object(body), youtube_post_headers())
+}
+
+/// WEB_EMBEDDED_PLAYER /player call. Carries embedUrl + signatureTimestamp.
+pub fn get_web_embedded_player_response(
+    video_id: &str,
+    localization: &Localization,
+    content_country: &ContentCountry,
+    signature_timestamp: i32,
+    po_token: Option<&str>,
+) -> Result<Value, ExtractionError> {
+    let info = InnertubeClientRequestInfo::of_web_embedded_player_client();
+    let embed_url = format!("https://www.youtube.com/embed/{video_id}");
+    let env = build_envelope(&info, localization, content_country, Some(&embed_url));
+    let mut body = envelope_to_body(env);
+    add_player_body_fields(&mut body, video_id, &generate_content_playback_nonce());
+    add_playback_context(&mut body, signature_timestamp, &embed_url);
+    if let Some(token) = po_token {
+        add_service_integrity_dimensions(&mut body, token);
+    }
+    let url = format!("{YOUTUBEI_V1_URL}player{DISABLE_PRETTY_PRINT_PARAM}");
+    post_youtube(&url, &Value::Object(body), youtube_post_headers())
+}
+
+/// ANDROID full /player call. Hits the gapis endpoint with the mobile
+/// header set. Caller must supply (cpn, po_token) — they are paired with
+/// the URLs the response will return; mixing them with iOS values returns
+/// 403.
+pub fn get_android_player_response(
+    video_id: &str,
+    localization: &Localization,
+    content_country: &ContentCountry,
+    cpn: &str,
+    po_token: Option<&str>,
+    visitor_data: Option<&str>,
+) -> Result<Value, ExtractionError> {
+    let mut info = InnertubeClientRequestInfo::of_android_client();
+    if let Some(v) = visitor_data {
+        info.client_info.visitor_data = Some(v.into());
+    }
+    let env = build_envelope(&info, localization, content_country, None);
+    let mut body = envelope_to_body(env);
+    add_player_body_fields(&mut body, video_id, cpn);
+    if let Some(token) = po_token {
+        add_service_integrity_dimensions(&mut body, token);
+    }
+    let url = format!(
+        "{YOUTUBEI_V1_GAPIS_URL}player{DISABLE_PRETTY_PRINT_PARAM}&t={t}&id={video_id}",
+        t = generate_content_playback_nonce()
+    );
+    let ua = android_user_agent(content_country);
+    post_youtube(&url, &Value::Object(body), mobile_post_headers(&ua))
+}
+
+/// ANDROID `/reel/reel_item_watch` fallback — used when no poToken is
+/// available. Returns a `playerResponse`-shaped JSON wrapped inside the
+/// reel response.
+pub fn get_android_reel_player_response(
+    video_id: &str,
+    localization: &Localization,
+    content_country: &ContentCountry,
+    cpn: &str,
+) -> Result<Value, ExtractionError> {
+    let info = InnertubeClientRequestInfo::of_android_client();
+    let env = build_envelope(&info, localization, content_country, None);
+    let mut body = envelope_to_body(env);
+    body.insert(
+        "playerRequest".into(),
+        json!({
+            "videoId": video_id,
+            "cpn": cpn,
+        }),
+    );
+    add_player_body_fields(&mut body, video_id, cpn);
+    let url = format!(
+        "{YOUTUBEI_V1_GAPIS_URL}reel/reel_item_watch{DISABLE_PRETTY_PRINT_PARAM}&t={t}&id={video_id}&$fields=playerResponse",
+        t = generate_content_playback_nonce()
+    );
+    let ua = android_user_agent(content_country);
+    post_youtube(&url, &Value::Object(body), mobile_post_headers(&ua))
+}
+
+/// IOS /player call. The iOS-progressive URLs returned here are subject
+/// to YT's ~917 KiB server-side cap — DO NOT route playback through
+/// these as the primary path. They're useful for HLS manifests on live
+/// streams. (See workspace memory/2026-05-24-night2-straw-vc18-rollback.md
+/// for the cap diagnostic.)
+pub fn get_ios_player_response(
+    video_id: &str,
+    localization: &Localization,
+    content_country: &ContentCountry,
+    cpn: &str,
+    po_token: Option<&str>,
+    visitor_data: Option<&str>,
+) -> Result<Value, ExtractionError> {
+    let mut info = InnertubeClientRequestInfo::of_ios_client();
+    if let Some(v) = visitor_data {
+        info.client_info.visitor_data = Some(v.into());
+    }
+    let env = build_envelope(&info, localization, content_country, None);
+    let mut body = envelope_to_body(env);
+    add_player_body_fields(&mut body, video_id, cpn);
+    if let Some(token) = po_token {
+        add_service_integrity_dimensions(&mut body, token);
+    }
+    let url = format!(
+        "{YOUTUBEI_V1_GAPIS_URL}player{DISABLE_PRETTY_PRINT_PARAM}&t={t}&id={video_id}",
+        t = generate_content_playback_nonce()
+    );
+    let ua = ios_user_agent(content_country);
+    post_youtube(&url, &Value::Object(body), mobile_post_headers(&ua))
+}
+
+fn post_youtube(
+    url: &str,
+    body: &Value,
+    headers: Vec<(String, String)>,
+) -> Result<Value, ExtractionError> {
+    let downloader = NewPipe::downloader().ok_or(ExtractionError::DownloaderMissing)?;
+    let serialized = serde_json::to_vec(body).map_err(|e| {
+        ExtractionError::Parsing(ParsingError::Invalid(format!("serialize body: {e}")))
+    })?;
+    let mut builder = Request::post(url, serialized);
+    for (k, v) in headers {
+        builder = builder.add_header(&k, &v);
+    }
+    let resp = downloader.execute(builder.build())?;
+    if resp.response_code() != 200 {
+        return Err(ExtractionError::Network(NetworkError::Transport(format!(
+            "HTTP {} from {url}",
+            resp.response_code()
+        ))));
+    }
+    let parsed: Value = serde_json::from_str(resp.response_body())
+        .map_err(|e| ExtractionError::Parsing(ParsingError::JsonShape(e.to_string())))?;
+    Ok(parsed)
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum ExtractionError {
+    #[error("network: {0}")]
+    Network(#[from] NetworkError),
+    #[error("parsing: {0}")]
+    Parsing(#[from] ParsingError),
+    #[error("downloader not initialized")]
+    DownloaderMissing,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn cpn_is_16_chars_alphanumeric() {
+        let cpn = generate_content_playback_nonce();
+        assert_eq!(cpn.len(), 16);
+        assert!(cpn
+            .chars()
+            .all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_'));
+    }
+
+    #[test]
+    fn two_consecutive_cpns_differ() {
+        // The nanos-seeded LCG advances monotonically — two back-to-back
+        // calls should produce different cpns.
+        let a = generate_content_playback_nonce();
+        std::thread::sleep(std::time::Duration::from_millis(2));
+        let b = generate_content_playback_nonce();
+        assert_ne!(a, b);
+    }
+}