lavu/channel_layout: change av_get_channel_layout() behavior at the next bump

The new syntax is preferred since it allows backward syntax compatibility
with libswr when switching to the new option handling code with
AV_OPT_TYPE_CHANNEL_LAYOUT.

With the new parser the string:
1234

is interpreted as a channel layout mask, rather than as a number of
channels, and thus it's compatible with the current way to set a channel
layout as an integer (e.g. for the icl and ocl options) making use of
integer option values.

ff_get_channel_layout() with compat=0 will be used in the
AV_OPT_TYPE_CHANNEL handler code.

The user is encouraged to switch to the new forward compatible syntax,
which requires to put a trailing "c" when specifying a layout as a number
of channels.

1 files changed, 6 insertions, 1 deletions

diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
index 2906098313..ba4f96d2d0 100644
--- a/libavutil/channel_layout.h
+++ b/libavutil/channel_layout.h
@@ -136,7 +136,12 @@ enum AVMatrixEncoding {
  * - a channel layout mask, in hexadecimal starting with "0x" (see the
  *   AV_CH_* macros).
  *
- * Example: "stereo+FC" = "2+FC" = "2c+1c" = "0x7"
+ * @warning Starting from the next major bump the trailing character
+ * 'c' to specify a number of channels will be required, while a
+ * channel layout mask could also be specified as a decimal number
+ * (if and only if not followed by "c").
+ *
+ * Example: "stereo+FC" = "2c+FC" = "2c+1c" = "0x7"
  */
 uint64_t av_get_channel_layout(const char *name);