player: add --demuxer-cache-wait option

DOCS/man/options.rst

@@ -2995,6 +2995,14 @@ Demuxer
     requests), seeking will be disabled. This option can forcibly enable it.
     For seeks within the cache, there's a good chance of success.
 
+``--demuxer-cache-wait=<yes|no>``
+    Before starting playback, read data until either the end of the file was
+    reached, or the demuxer cache has reached maximum capacity. Only once this
+    is done, playback starts. This intentionally happens before the initial
+    seek triggered with ``--start``. This does not change any runtime behavior
+    after the initial caching. This option is useless if the file cannot be
+    cached completely.
+
 Input
 -----
 

demux/demux.c

@@ -1100,6 +1100,17 @@ void demux_set_wakeup_cb(struct demuxer *demuxer, void (*cb)(void *ctx), void *c
     pthread_mutex_unlock(&in->lock);
 }
 
+void demux_start_prefetch(struct demuxer *demuxer)
+{
+    struct demux_internal *in = demuxer->in;
+    assert(demuxer == in->d_user);
+
+    pthread_mutex_lock(&in->lock);
+    in->reading = true;
+    pthread_cond_signal(&in->wakeup);
+    pthread_mutex_unlock(&in->lock);
+}
+
 const char *stream_type_name(enum stream_type type)
 {
     switch (type) {

demux/demux.h

@@ -260,6 +260,7 @@ struct demuxer *demux_open_url(const char *url,
 void demux_start_thread(struct demuxer *demuxer);
 void demux_stop_thread(struct demuxer *demuxer);
 void demux_set_wakeup_cb(struct demuxer *demuxer, void (*cb)(void *ctx), void *ctx);
+void demux_start_prefetch(struct demuxer *demuxer);
 
 bool demux_cancel_test(struct demuxer *demuxer);
 

options/options.c

@@ -460,6 +460,7 @@ const m_option_t mp_opts[] = {
     OPT_STRING("sub-demuxer", sub_demuxer_name, 0),
     OPT_FLAG("demuxer-thread", demuxer_thread, 0),
     OPT_DOUBLE("demuxer-termination-timeout", demux_termination_timeout, 0),
+    OPT_FLAG("demuxer-cache-wait", demuxer_cache_wait, 0),
     OPT_FLAG("prefetch-playlist", prefetch_open, 0),
     OPT_FLAG("cache-pause", cache_pause, 0),
     OPT_FLAG("cache-pause-initial", cache_pause_initial, 0),

options/options.h

@@ -248,6 +248,7 @@ typedef struct MPOpts {
     char *demuxer_name;
     int demuxer_thread;
     double demux_termination_timeout;
+    int demuxer_cache_wait;
     int prefetch_open;
     char *audio_demuxer_name;
     char *sub_demuxer_name;

player/loadfile.c

@@ -1534,6 +1534,19 @@ static void play_current_file(struct MPContext *mpctx)
         goto terminate_playback;
     }
 
+    demux_start_prefetch(mpctx->demuxer);
+
+    if (opts->demuxer_cache_wait) {
+        while (!mpctx->stop_play) {
+            struct demux_reader_state s;
+            demux_get_reader_state(mpctx->demuxer, &s);
+            if (s.idle)
+                break;
+
+            mp_idle(mpctx);
+        }
+    }
+
     double play_start_pts = get_play_start_pts(mpctx);
     if (play_start_pts != MP_NOPTS_VALUE) {
         /*