Fix subtitle language parsing: PGS in audio slots, secondary PG entries

Two MPLS parsing issues:

1. PGS subtitle (0x90) appearing in audio stream slot: language was read
 from audio offset sa[2..5] instead of PG offset sa[1..4], causing
 truncation ("ng " instead of "eng"). Fixed by detecting PGS coding
 type in audio slots and using correct offset.

2. Secondary PG (PiP subtitle) entries were not consumed, causing
 position tracking to drift. Added missing n_pip_pg loop.

3. Added stream_type 5/6/7 attribute parsing for secondary audio/video.

src/mpls.rs

@@ -111,7 +111,7 @@ pub fn parse(data: &[u8]) -> Result<Playlist> {
             let n_ig = item[STN_OFFSET + 7] as usize;
             let n_sec_audio = item[STN_OFFSET + 8] as usize;
             let n_sec_video = item[STN_OFFSET + 9] as usize;
-            let _n_pip_pg = item[STN_OFFSET + 10] as usize;
+            let n_pip_pg = item[STN_OFFSET + 10] as usize;
             let n_dv = item[STN_OFFSET + 11] as usize;
 
             let mut spos = STN_OFFSET + 16;
@@ -173,6 +173,18 @@ pub fn parse(data: &[u8]) -> Result<Playlist> {
                     } else { spos = next; }
                 } else { break; }
             }
+            // Secondary PG (PiP subtitles) — must consume to keep spos aligned
+            for _ in 0..n_pip_pg {
+                if let Some((mut entry, next)) = parse_stream_entry(item, spos, 3) {
+                    entry.secondary = true;
+                    streams.push(entry);
+                    // Skip reference data: num_refs(1) + reserved(1) + refs + padding
+                    if next < item.len() {
+                        let n_refs = item[next] as usize;
+                        spos = next + 2 + n_refs + (n_refs % 2);
+                    } else { spos = next; }
+                } else { break; }
+            }
             // Dolby Vision enhancement layer
             for _ in 0..n_dv {
                 if let Some((mut entry, next)) = parse_stream_entry(item, spos, 1) {
@@ -227,6 +239,7 @@ fn parse_stream_entry(item: &[u8], pos: usize, stream_type: u8) -> Option<(Strea
     let sa = &item[se_end + 1..se_end + 1 + sa_len];
     let coding_type = sa[0];
 
+
     let mut video_format = 0u8;
     let mut video_rate = 0u8;
     let mut audio_format = 0u8;
@@ -249,12 +262,19 @@ fn parse_stream_entry(item: &[u8], pos: usize, stream_type: u8) -> Option<(Strea
         }
         2 => {
             // Audio: coding_type(1) + format_rate(1) + language(3)
-            if sa.len() >= 2 {
-                audio_format = (sa[1] >> 4) & 0x0F;
-                audio_rate = sa[1] & 0x0F;
-            }
-            if sa.len() >= 5 {
-                language = String::from_utf8_lossy(&sa[2..5]).to_string();
+            // Exception: PGS (0x90/0x91) in audio slot uses PG layout: coding_type(1) + language(3)
+            if coding_type == 0x90 || coding_type == 0x91 {
+                if sa.len() >= 4 {
+                    language = String::from_utf8_lossy(&sa[1..4]).to_string();
+                }
+            } else {
+                if sa.len() >= 2 {
+                    audio_format = (sa[1] >> 4) & 0x0F;
+                    audio_rate = sa[1] & 0x0F;
+                }
+                if sa.len() >= 5 {
+                    language = String::from_utf8_lossy(&sa[2..5]).to_string();
+                }
             }
         }
         3 | 4 => {