[FFmpeg-devel] [PATCH] Make decoding alpha optional for some codecs.

[Michael Niedermayer]

On Wed, Sep 18, 2013 at 07:36:55PM +0200, Reimar Döffinger wrote:
> For codecs where decoding of a whole plane can simply
> be skipped, we should offer applications to not decode
> alpha for better performance (ca. 30% less CPU usage
> and 40% reduced memory bandwidth).
> It also means applications do not need to implement support
> (even if it is rather simple) for YUVA formats in order to be
> able to play these files.
> Tested by manually hacking avcodec_default_get_format,
> suggestions for how to test in FATE welcome.
> 
> Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
> ---
>  Changelog                               |  2 +
>  libavcodec/avcodec.h                    |  1 +
>  libavcodec/ffv1dec.c                    |  1 +
>  libavcodec/options_table.h              |  1 +
>  libavcodec/proresdec2.c                 |  1 +
>  libavcodec/proresdec_lgpl.c             |  3 +-
>  libavcodec/vp56.c                       |  7 +--
>  tests/fate/prores.mak                   |  4 ++
>  tests/fate/vpx.mak                      |  3 ++
>  tests/ref/fate/prores-alpha_skip        |  3 ++
>  tests/ref/fate/prores-transparency_skip |  5 ++
>  tests/ref/fate/vp6a-skip_alpha          | 94 +++++++++++++++++++++++++++++++++
>  12 files changed, 121 insertions(+), 4 deletions(-)
>  create mode 100644 tests/ref/fate/prores-alpha_skip
>  create mode 100644 tests/ref/fate/prores-transparency_skip
>  create mode 100644 tests/ref/fate/vp6a-skip_alpha
> 
> diff --git a/Changelog b/Changelog
> index 3e4653b..4ffbc5a 100644
> --- a/Changelog
> +++ b/Changelog
> @@ -25,6 +25,8 @@ version <next>
>    more consistent with other muxers.
>  - adelay filter
>  - pullup filter ported from libmpcodecs
> +- make decoding alpha optional for prores, ffv1 and vp6 by setting
> +  the skip_alpha flag.
>  
>  
>  version 2.0:
> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
> index 23fba4f..505283b 100644
> --- a/libavcodec/avcodec.h
> +++ b/libavcodec/avcodec.h

> @@ -720,6 +720,7 @@ typedef struct RcOverride{
>  
>  #define CODEC_FLAG2_CHUNKS        0x00008000 ///< Input bitstream might be truncated at a packet boundaries instead of only at frame boundaries.
>  #define CODEC_FLAG2_SHOW_ALL      0x00400000 ///< Show all frames before the first keyframe
> +#define CODEC_FLAG2_SKIP_ALPHA    0x00800000 ///< Skip processing alpha if supported by codec

I suggest to use a field (int or whatever) in the context instead
of a flag. It reduces the chance of conflicts with additions from
forks

[...]

Thanks

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

No human being will ever know the Truth, for even if they happen to say it
by chance, they would not even known they had done so. -- Xenophanes
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