demux: add --demuxer-hysteresis-bytes

Fixes: https://github.com/mpv-player/mpv/discussions/17888#discussioncomment-16852506

DOCS/interface-changes/demuxer-hysteresis-bytes.txt

@@ -0,0 +1 @@
+add `--demuxer-hysteresis-bytes`

DOCS/man/options.rst

@@ -4334,6 +4334,19 @@ Demuxer
     The default value is 0 seconds, which disables the caching hysteresis. A
     value of 10 seconds probably works well for most usecases.
 
+``--demuxer-hysteresis-bytes=<bytesize>``
+    Same as ``--demuxer-hysteresis-secs``, but specifies the hysteresis in
+    bytes of forward buffered data instead of seconds. Once the demuxer limit
+    is reached, the demuxer will not buffer ahead again until the amount of
+    forward buffered data drops to this value.
+
+    This option is useful for streams with variable or unknown bitrate, where
+    a byte-based threshold is more meaningful than a time-based one. It can
+    also be combined with ``--demuxer-hysteresis-secs``. In that case buffering
+    can resume when either threshold is reached.
+
+    The default value is 0, which disables the byte-based caching hysteresis.
+
 ``--prefetch-playlist=<yes|no>``
     Prefetch next playlist entry while playback of the current entry is ending
     (default: no). This merely opens the URL of the next playlist entry as soon

demux/demux.c

@@ -102,6 +102,8 @@ const struct m_sub_options demux_conf = {
         {"cache-on-disk", OPT_BOOL(disk_cache)},
         {"demuxer-readahead-secs", OPT_DOUBLE(min_secs), M_RANGE(0, DBL_MAX)},
         {"demuxer-hysteresis-secs", OPT_DOUBLE(hyst_secs), M_RANGE(0, DBL_MAX)},
+        {"demuxer-hysteresis-bytes", OPT_BYTE_SIZE(hyst_bytes),
+            M_RANGE(0, M_MAX_MEM_BYTES)},
         {"demuxer-max-bytes", OPT_BYTE_SIZE(max_bytes),
             M_RANGE(0, M_MAX_MEM_BYTES)},
         {"demuxer-max-back-bytes", OPT_BYTE_SIZE(max_bytes_bw),
@@ -201,6 +203,7 @@ struct demux_internal {
     bool eof;                   // whether we're in EOF state
     double min_secs;
     double hyst_secs;           // stop reading till there's hyst_secs remaining
+    size_t hyst_bytes;          // stop reading till there's hyst_bytes remaining
     bool hyst_active;
     size_t max_bytes;
     size_t max_bytes_bw;
@@ -2275,12 +2278,17 @@ static bool read_packet(struct demux_internal *in)
         total_fw_bytes += get_forward_buffered_bytes(ds);
     }
 
+    if (in->hyst_bytes > 0 && total_fw_bytes <= in->hyst_bytes) {
+        in->hyst_active = false;
+        prefetch_more |= true;
+    }
+
     MP_TRACE(in, "bytes=%zd, read_more=%d prefetch_more=%d, refresh_more=%d\n",
              (size_t)total_fw_bytes, read_more, prefetch_more, refresh_more);
     if (total_fw_bytes >= in->max_bytes) {
         // if we hit the limit just by prefetching, simply stop prefetching
         if (!read_more) {
-            in->hyst_active = !!in->hyst_secs;
+            in->hyst_active = in->hyst_secs > 0 || in->hyst_bytes > 0;
             return false;
         }
         if (!in->warned_queue_overflow) {
@@ -2313,7 +2321,7 @@ static bool read_packet(struct demux_internal *in)
     }
 
     if (!read_more && !prefetch_more && !refresh_more) {
-        in->hyst_active = !!in->hyst_secs;
+        in->hyst_active = in->hyst_secs > 0 || in->hyst_bytes > 0;
         return false;
     }
 
@@ -2533,6 +2541,7 @@ static void update_opts(struct demuxer *demuxer)
 
     in->min_secs = opts->min_secs;
     in->hyst_secs = opts->hyst_secs;
+    in->hyst_bytes = opts->hyst_bytes;
     in->max_bytes = opts->max_bytes;
     in->max_bytes_bw = opts->max_bytes_bw;
 

demux/demux.h

@@ -71,6 +71,7 @@ struct demux_opts {
     bool donate_fw;
     double min_secs;
     double hyst_secs;
+    int64_t hyst_bytes;
     bool force_seekable;
     double min_secs_cache;
     bool access_references;