[FFmpeg-devel] [PATCH 4/4] mmaldec: limit internal buffering

[Michael Niedermayer]

On Wed, Jan 27, 2016 at 05:17:56PM +0100, wm4 wrote:
> This uses a new MMAL feature, which limits the number of extra frames
> that can be buffered within the decoder. VIDEO_MAX_NUM_CALLBACKS can
> be defined as positive or negative number. Positive numbers are
> absolute, and can lead to deadlocks if the user underestimates the
> required buffers. Negative numbers specify the number of extra
> buffers, e.g. -1 means no extra buffer, (-1-N) means N extra buffers.
> 
> Set a gratuitous default of -11 (N=10). This is much lower than the
> firmware default, which appears to be 96.
> 
> This is backwards compatible, but needs a symbol only present in newer
> firmware headers. (It's an enum item, so it requires a check in
> configure.)
> ---
>  configure            | 4 ++++
>  libavcodec/mmaldec.c | 7 +++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/configure b/configure
> index 9b195c9..e5f513b 100755
> --- a/configure
> +++ b/configure
> @@ -5546,6 +5546,10 @@ enabled mmal              && { check_lib interface/mmal/mmal.h mmal_port_connect
>                                      check_lib interface/mmal/mmal.h mmal_port_connect ; }
>                                  check_lib interface/mmal/mmal.h mmal_port_connect ; } ||
>                                 die "ERROR: mmal not found"; }
> +enabled mmal &&
> +    check_code cc interface/mmal/mmal.h "MMAL_PARAMETER_VIDEO_MAX_NUM_CALLBACKS" ||
> +    die "ERROR: mmal firmware headers too old"
> +
>  enabled netcdf            && require_pkg_config netcdf netcdf.h nc_inq_libvers
>  enabled nvenc             && { check_header nvEncodeAPI.h || die "ERROR: nvEncodeAPI.h not found."; } &&
>                               { check_cpp_condition nvEncodeAPI.h "NVENCAPI_MAJOR_VERSION >= 5" ||

this or a previous change breaks build
make distclean ; ../configure --cc='ccache x86_64-w64-mingw32-gcc' --arch=x86_64 --target-os=mingw32 --cross-prefix=x86_64-w64-mingw32- && make -j12
ERROR: mmal firmware headers too old


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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