feat(mediaplayer): HLS / Low-Latency HLS playback (Windows)

Add an HLS source layered on top of the existing OS-codec media player. It
parses the M3U8, selects a single rendition, starts near the live edge, and
stitches segments (and LL-HLS EXT-X-PART parts) into one continuous byte stream
that the existing MPEG-TS / fragmented-MP4 demuxers consume. A background reader
paces delivery to the stream's measured average bitrate so the wall-clock
present path is fed at real time (not flooded), with enough burst to deliver
segment-start keyframes promptly.

Scope: Windows (WinHTTP fetch), clear streams, single rendition. Android/Quest
support is planned.

The existing RTSP and MPEG-TS implementations are NOT touched — basis_rtsp.c,
basis_ts.c (and basis_rtmp.c, basis_mp4.c, basis_http.c, basis_url.c, the
Windows decode/HTTP backends) have zero source edits. basis_media_core.c only
gains an additive ".m3u8" branch ahead of the plain byte-source path; every
other URL (rtsp/rtmp/.ts/.mp4) takes the identical existing route. No C# changes.

- protocol/basis_hls.c/.h: new HLS source (M3U8 parse, segment/part scheduler,
  paced read-ahead buffer)
- basis_media_core.c: route .m3u8 to the HLS source, feeding basis_ts_run /
  basis_mp4_run unchanged
- CMakeLists.txt: add basis_hls.c to the portable core
- README.md: document HLS support and the Windows / clear / single-rendition scope

Author: towneh

Basis/Packages/com.basis.mediaplayer/Native~/CMakeLists.txt

@@ -67,6 +67,7 @@ set(CORE_SOURCES
     protocol/basis_rtmp.c
     protocol/basis_ts.c
     protocol/basis_mp4.c
+    protocol/basis_hls.c
 )
 
 # ---------------------------------------------------------------------------

Basis/Packages/com.basis.mediaplayer/Native~/basis_media_core.c

@@ -21,6 +21,7 @@
 #include "protocol/basis_ts.h"
 #include "protocol/basis_mp4.h"
 #include "protocol/basis_http.h"
+#include "protocol/basis_hls.h"
 
 #include <stdlib.h>
 #include <string.h>
@@ -192,6 +193,32 @@ static int ends_with_ci(const char* s, const char* suffix) {
     return 1;
 }
 
+/* HLS / LL-HLS: the URL is a playlist, not a continuous byte stream. The HLS
+ * source fetches+parses the M3U8, stitches segments (and LL-HLS parts) into one
+ * byte stream, and the existing TS/fMP4 demuxers consume it. Windows fetches via
+ * WinHTTP; Android/Quest support is planned. */
+static void run_hls(basis_media_engine_t* e) {
+#if defined(_WIN32)
+    basis_http_provider_t provider = {
+        basis_win_http_open, basis_win_http_read, basis_win_http_close
+    };
+    int is_fmp4 = 0;
+    void* hls = basis_hls_open(e->url, &provider, e->sink.is_running, e->sink.user, &is_fmp4);
+    if (!hls) {
+        basis_engine_set_error(e, "failed to open HLS playlist");
+        return;
+    }
+    basis_engine_set_state(e, BASIS_MEDIA_STATE_BUFFERING);
+    if (is_fmp4)
+        basis_mp4_run(&e->sink, basis_hls_read, hls);
+    else
+        basis_ts_run(&e->sink, basis_hls_read, hls);
+    basis_hls_close(hls);
+#else
+    basis_engine_set_error(e, "HLS playback currently requires the Windows backend.");
+#endif
+}
+
 static void run_http_like(basis_media_engine_t* e) {
     /* Android: the OS extractor can demux the URL itself (TLS included). */
     if (basis_decoder_try_open_url(e->decoder, e->url)) {
@@ -200,6 +227,13 @@ static void run_http_like(basis_media_engine_t* e) {
         return;
     }
 
+    /* HLS playlists are not a single continuous stream — hand off to the HLS
+     * source before the plain TS/fMP4 byte-source path. (.m3u8 may carry a query.) */
+    if (strstr(e->parts.path, ".m3u8")) {
+        run_hls(e);
+        return;
+    }
+
     void* src = NULL;
     basis_read_fn rd = NULL;