[FFmpeg-devel] [PATCH 001/279] Add a new channel layout API

[Anton Khirnov]

Quoting Lynne (2021-12-08 13:57:45)
> 8 Dec 2021, 13:16 by anton at khirnov.net:
> 
> > Quoting Lynne (2021-12-08 10:02:34)
> >
> >> 8 Dec 2021, 02:06 by jamrial at gmail.com:
> >>
> >> > From: Anton Khirnov <anton at khirnov.net>
> >> >
> >> > The new API is more extensible and allows for custom layouts.
> >> > More accurate information is exported, eg for decoders that do not
> >> > set a channel layout, lavc will not make one up for them.
> >> >
> >> > Deprecate the old API working with just uint64_t bitmasks.
> >> >
> >> > Expanded and completed by Vittorio Giovara <vittorio.giovara at gmail.com>
> >> > and James Almer <jamrial at gmail.com>.
> >> > Signed-off-by: Vittorio Giovara <vittorio.giovara at gmail.com>
> >> > Signed-off-by: James Almer <jamrial at gmail.com>
> >> > ---
> >> >  libavutil/channel_layout.c | 498 ++++++++++++++++++++++++++++++------
> >> >  libavutil/channel_layout.h | 510 ++++++++++++++++++++++++++++++++++---
> >> >  libavutil/version.h        |   1 +
> >> >  3 files changed, 906 insertions(+), 103 deletions(-)
> >> > 
> >> >  /**
> >> >  * @}
> >> > @@ -128,6 +199,157 @@ enum AVMatrixEncoding {
> >> >  AV_MATRIX_ENCODING_NB
> >> >  };
> >> > 
> >> > +/**
> >> > + * @}
> >> > + */
> >> > +
> >> > +/**
> >> > + * An AVChannelCustom defines a single channel within a custom order layout
> >> > + *
> >> > + * Unlike most structures in FFmpeg, sizeof(AVChannelCustom) is a part of the
> >> > + * public ABI.
> >> > + *
> >> > + * No new fields may be added to it without a major version bump.
> >> > + */
> >> > +typedef struct AVChannelCustom {
> >> > +    enum AVChannel id;
> >> > +} AVChannelCustom;
> >> >
> >>
> >> Consider adding a 25-byte or so of a description field string here that
> >> would also be copied if the frame/layout is copied?
> >> That way, users can assign a description label to each channel,
> >> for example labeling each channel in a 255 channel custom layout
> >> Opus stream used in production at a venue somewhere.
> >> Also, consider additionally reserving 16-bytes here, just in case.
> >>
> >
> > That would enlarge the layout size by a significant amount. Keep in mind
> > that this is all per frame. And for something that very few people would
> > want to use.
> >
> > These descriptors, if anyone really needs them, can live in side data.
> >
> 
> That's fine with me.
> Can we at least have an opaque uint64_t? I'd accept a uintptr_t,
> or an int too, or even a single-byte uint8_t.

like this?

diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
index 7b77a74b61..7b2ba12532 100644
--- a/libavutil/channel_layout.h
+++ b/libavutil/channel_layout.h
@@ -252,7 +252,8 @@ enum AVMatrixEncoding {
  * No new fields may be added to it without a major version bump.
  */
 typedef struct AVChannelCustom {
-    enum AVChannel id;
+    enum AVChannel id:16;
+    int      reserved:16;
 } AVChannelCustom;
 
 /**

-- 
Anton Khirnov