--- a/libavcodec/parser.c	2026-07-08 19:57:50.741008542 +0000
+++ b/libavcodec/parser.c	2026-07-08 19:58:15.847310863 +0000
@@ -200,9 +200,34 @@
     }
 }
 
+/* yauiclient/NextPVR: 512KiB is comfortably above the ~200-350KB
+ * high-water-marks observed during ordinary playback (so normal
+ * legitimate peaks aren't churned every time), and well below the
+ * 8MiB catastrophic-case resync valve in
+ * mpegvideo_parser_resync_valve.patch. See ff_combine_frame() below
+ * for full rationale. */
+#define YAUI_MPV_PARSER_SHRINK_THRESHOLD (512 * 1024)
+
 int ff_combine_frame(ParseContext *pc, int next,
                      const uint8_t **buf, int *buf_size)
 {
+    /* yauiclient/NextPVR: proactively shrink pc->buffer's high-water-mark
+     * capacity if it's grown unreasonably large. av_fast_realloc() only
+     * ever grows a buffer, never shrinks it - by design, to avoid realloc
+     * churn on the common case of similar-sized calls. But on a live
+     * MPEG-2 stream where mpeg1_find_frame_end()'s state machine
+     * occasionally needs several calls to resolve a frame boundary, each
+     * such episode ratchets buffer_size up a step and it never comes back
+     * down on its own. Only safe here, at the top of the function, when
+     * pc->index == 0: that means no partial-frame accumulation is
+     * currently in flight, so pc->buffer isn't about to be handed back
+     * to the caller via *buf this call.
+     */
+    if (pc->index == 0 && pc->buffer_size > YAUI_MPV_PARSER_SHRINK_THRESHOLD) {
+        av_freep(&pc->buffer);
+        pc->buffer_size = 0;
+    }
+
     if (pc->overread) {
         ff_dlog(NULL, "overread %d, state:%"PRIX32" next:%d index:%d o_index:%d\n",
                 pc->overread, pc->state, next, pc->index, pc->overread_index);