audio/filter: split af_format into separate filters, rename af_force

af_format is the old audio conversion filter. It could do all possible
conversions supported by the audio chain. However, ever since the
addition of af_lavrresample, most conversions are done by
libav/swresample, and af_format is used as fallback.

Separate out the fallback cases and remove af_format. af_convert24 does
24 bit <-> 32 bit conversions, while af_convertsignendian does sign and
endian conversions. Maybe the way the conversions are split sounds a bit
odd. But the former changes the size of the audio data, while the latter
is fully in-place, so there's at least different buffer management.

This requires a quite complicated algorithm to make sure all these
"partial" conversion filters can actually get from one format to
another. E.g. s24le->s32be always requires convertsignendian and
convert24, but af.c has no idea what the intermediate format should
be. So I added a graph search (trying every possible format and
filter) to determine required format and filter. When I wrote this,
it seemed this was still better than messing everything into
af_lavrresample, but maybe this is overkill and I'll change my
opinion. For now, it seems nice to get rid of af_format though.

The AC3->IEC61937 conversion isn't supported anymore, but I don't think
this is needed anywhere. Most AOs test all formats explicitly, or use
the AF_FORMAT_IS_IEC61937() macro (which includes AC3).

One positive consequence of this change is that conversions always
include dithering (done by libav/swresample), instead of possibly going
through af_format, which doesn't do anything fancy.

Rename af_force to af_format. It's essentially compatible with command
line uses of af_format. We retain a compatibility alias for af_force.

1 files changed, 4 insertions, 4 deletions

diff --git a/audio/filter/af_force.c b/audio/filter/af_force.c
index adf17c61f2..21af663e81 100644
--- a/audio/filter/af_force.c
+++ b/audio/filter/af_force.c
@@ -72,12 +72,12 @@ static int control(struct af_instance *af, int cmd, void *arg)
 
         if (in->nch != out->nch || in->bps != out->bps) {
             mp_msg(MSGT_AFILTER, MSGL_ERR,
-                   "[af_force] Forced input/output formats are incompatible.\n");
+                   "[af_format] Forced input/output formats are incompatible.\n");
             return AF_ERROR;
         }
 
         if (priv->fail) {
-            mp_msg(MSGT_AFILTER, MSGL_ERR, "[af_force] Failing on purpose.\n");
+            mp_msg(MSGT_AFILTER, MSGL_ERR, "[af_format] Failing on purpose.\n");
             return AF_ERROR;
         }
 
@@ -116,9 +116,9 @@ static int af_open(struct af_instance *af)
 
 #define OPT_BASE_STRUCT struct priv
 
-struct af_info af_info_force = {
+struct af_info af_info_format = {
     "Force audio format",
-    "force",
+    "format",
     "",
     "",
     0,