audio: don't recreate AO if a filter changes the output format

Until recently, the AO was reinitialized strictly only on decoder format
changes. But the commit for simplifying audio format negotiation removed
this. Now the AO is recreated for any format change.

This is sort of annoying if you change playback speed. The
insertion/removal of af_scaletempo can change the sample format. For
example, the acompressor filter will convert output to double, so
toggling scaletempo will force the format back to float. This recreates
the AO under the --gapless-audio=weak default. This likely affects a lot
of other filters too.

Work this around by allowing sample format changes, and keeping the
current AO format in these cases. This is probably not a big problem.
Most audio APIs force the output format to float anyway.

This means you actually have to worry about what the default gapless
mode does to your audio. If you start with a file that uses 8 bit per
sample, and then continue playing a 24 bit FLAC, it will be converted
down to 8 bit per sample. (Assuming they are played in a way that uses
the gapless logic.)

1 files changed, 28 insertions, 1 deletions

diff --git a/player/audio.c b/player/audio.c
index a6b7601df2..842d965d49 100644
--- a/player/audio.c
+++ b/player/audio.c
@@ -255,6 +255,33 @@ static char *audio_config_to_str_buf(char *buf, size_t buf_sz, int rate,
     return buf;
 }
 
+// Decide whether on a format change, we should reinit the AO.
+static bool keep_weak_gapless_format(struct mp_aframe *old, struct mp_aframe* new)
+{
+    bool res = false;
+    struct mp_aframe *new_mod = mp_aframe_new_ref(new);
+    if (!new_mod)
+        abort();
+
+    // If the sample formats are compatible (== libswresample generally can
+    // convert them), keep the AO. On other changes, recreate it.
+
+    int old_fmt = mp_aframe_get_format(old);
+    int new_fmt = mp_aframe_get_format(new);
+
+    if (af_format_conversion_score(old_fmt, new_fmt) == INT_MIN)
+        goto done; // completely incompatible formats
+
+    if (!mp_aframe_set_format(new_mod, old_fmt))
+        goto done;
+
+    res = mp_aframe_config_equals(old, new_mod);
+
+done:
+    talloc_free(new_mod);
+    return res;
+}
+
 static void reinit_audio_filters_and_output(struct MPContext *mpctx)
 {
     struct MPOpts *opts = mpctx->opts;
@@ -290,7 +317,7 @@ static void reinit_audio_filters_and_output(struct MPContext *mpctx)
     // previous one, keep the AO and don't reinit anything.
     // Strong gapless: always keep the AO
     if ((mpctx->ao_filter_fmt && mpctx->ao && opts->gapless_audio < 0 &&
-         mp_aframe_config_equals(mpctx->ao_filter_fmt, out_fmt)) ||
+         keep_weak_gapless_format(mpctx->ao_filter_fmt, out_fmt)) ||
         (mpctx->ao && opts->gapless_audio > 0))
     {
         mp_output_chain_set_ao(ao_c->filter, mpctx->ao);