[FFmpeg-devel] [PATCH] Add a new channel layout API
Nicolas George
george at nsup.org
Wed Dec 26 16:22:26 EET 2018
Paul B Mahol (2018-12-24):
> 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.
>
> Original commit by Anton Khirnov <anton at khirnov.net>.
> Expanded and completed by Vittorio Giovara <vittorio.giovara at gmail.com>.
> Adopted for FFmpeg by Paul B Mahol <onemda at gmail.com>.
Adapted?
Reviewing only the visible API for now.
> diff --git a/libavutil/channel_layout.h b/libavutil/channel_layout.h
> index 50bb8f03c5..e6c8c58b9c 100644
> --- a/libavutil/channel_layout.h
> +++ b/libavutil/channel_layout.h
> @@ -24,6 +24,9 @@
>
> #include <stdint.h>
>
> +#include "version.h"
> +#include "attributes.h"
> +
> /**
> * @file
> * audio channel layout utility functions
> @@ -34,6 +37,60 @@
> * @{
> */
>
> +enum AVChannel {
> + AV_CHAN_FRONT_LEFT,
> + AV_CHAN_FRONT_RIGHT,
> + AV_CHAN_FRONT_CENTER,
> + AV_CHAN_LOW_FREQUENCY,
> + AV_CHAN_BACK_LEFT,
> + AV_CHAN_BACK_RIGHT,
> + AV_CHAN_FRONT_LEFT_OF_CENTER,
> + AV_CHAN_FRONT_RIGHT_OF_CENTER,
> + AV_CHAN_BACK_CENTER,
> + AV_CHAN_SIDE_LEFT,
> + AV_CHAN_SIDE_RIGHT,
> + AV_CHAN_TOP_CENTER,
> + AV_CHAN_TOP_FRONT_LEFT,
> + AV_CHAN_TOP_FRONT_CENTER,
> + AV_CHAN_TOP_FRONT_RIGHT,
> + AV_CHAN_TOP_BACK_LEFT,
> + AV_CHAN_TOP_BACK_CENTER,
> + AV_CHAN_TOP_BACK_RIGHT,
> + /** Stereo downmix. */
> + AV_CHAN_STEREO_LEFT = 29,
> + /** See above. */
> + AV_CHAN_STEREO_RIGHT,
> + AV_CHAN_WIDE_LEFT,
> + AV_CHAN_WIDE_RIGHT,
> + AV_CHAN_SURROUND_DIRECT_LEFT,
> + AV_CHAN_SURROUND_DIRECT_RIGHT,
> + AV_CHAN_LOW_FREQUENCY_2,
> +
> + /** Channel is empty can be safely skipped. */
> + AV_CHAN_SILENCE = 64,
> +};
> +
> +enum AVChannelOrder {
> + /**
> + * The native channel order, i.e. the channels are in the same order in
> + * which they are defined in the AVChannel enum. This supports up to 63
> + * different channels.
> + */
> + AV_CHANNEL_ORDER_NATIVE,
> + /**
> + * The channel order does not correspond to any other predefined order and
> + * is stored as an explicit map. For example, this could be used to support
> + * layouts with 64 or more channels, or with channels that could be skipped.
> + */
> + AV_CHANNEL_ORDER_CUSTOM,
> + /**
> + * Only the channel count is specified, without any further information
> + * about the channel order.
> + */
> + AV_CHANNEL_ORDER_UNSPEC,
> +};
> +
> +
> /**
> * @defgroup channel_masks Audio channel masks
> *
> @@ -46,36 +103,41 @@
> *
> * @{
> */
> -#define AV_CH_FRONT_LEFT 0x00000001
> -#define AV_CH_FRONT_RIGHT 0x00000002
> -#define AV_CH_FRONT_CENTER 0x00000004
> -#define AV_CH_LOW_FREQUENCY 0x00000008
> -#define AV_CH_BACK_LEFT 0x00000010
> -#define AV_CH_BACK_RIGHT 0x00000020
> -#define AV_CH_FRONT_LEFT_OF_CENTER 0x00000040
> -#define AV_CH_FRONT_RIGHT_OF_CENTER 0x00000080
> -#define AV_CH_BACK_CENTER 0x00000100
> -#define AV_CH_SIDE_LEFT 0x00000200
> -#define AV_CH_SIDE_RIGHT 0x00000400
> -#define AV_CH_TOP_CENTER 0x00000800
> -#define AV_CH_TOP_FRONT_LEFT 0x00001000
> -#define AV_CH_TOP_FRONT_CENTER 0x00002000
> -#define AV_CH_TOP_FRONT_RIGHT 0x00004000
> -#define AV_CH_TOP_BACK_LEFT 0x00008000
> -#define AV_CH_TOP_BACK_CENTER 0x00010000
> -#define AV_CH_TOP_BACK_RIGHT 0x00020000
> -#define AV_CH_STEREO_LEFT 0x20000000 ///< Stereo downmix.
> -#define AV_CH_STEREO_RIGHT 0x40000000 ///< See AV_CH_STEREO_LEFT.
> -#define AV_CH_WIDE_LEFT 0x0000000080000000ULL
> -#define AV_CH_WIDE_RIGHT 0x0000000100000000ULL
> -#define AV_CH_SURROUND_DIRECT_LEFT 0x0000000200000000ULL
> -#define AV_CH_SURROUND_DIRECT_RIGHT 0x0000000400000000ULL
> -#define AV_CH_LOW_FREQUENCY_2 0x0000000800000000ULL
> +#define AV_CH_FRONT_LEFT (1ULL << AV_CHAN_FRONT_LEFT )
> +#define AV_CH_FRONT_RIGHT (1ULL << AV_CHAN_FRONT_RIGHT )
> +#define AV_CH_FRONT_CENTER (1ULL << AV_CHAN_FRONT_CENTER )
> +#define AV_CH_LOW_FREQUENCY (1ULL << AV_CHAN_LOW_FREQUENCY )
> +#define AV_CH_BACK_LEFT (1ULL << AV_CHAN_BACK_LEFT )
> +#define AV_CH_BACK_RIGHT (1ULL << AV_CHAN_BACK_RIGHT )
> +#define AV_CH_FRONT_LEFT_OF_CENTER (1ULL << AV_CHAN_FRONT_LEFT_OF_CENTER )
> +#define AV_CH_FRONT_RIGHT_OF_CENTER (1ULL << AV_CHAN_FRONT_RIGHT_OF_CENTER)
> +#define AV_CH_BACK_CENTER (1ULL << AV_CHAN_BACK_CENTER )
> +#define AV_CH_SIDE_LEFT (1ULL << AV_CHAN_SIDE_LEFT )
> +#define AV_CH_SIDE_RIGHT (1ULL << AV_CHAN_SIDE_RIGHT )
> +#define AV_CH_TOP_CENTER (1ULL << AV_CHAN_TOP_CENTER )
> +#define AV_CH_TOP_FRONT_LEFT (1ULL << AV_CHAN_TOP_FRONT_LEFT )
> +#define AV_CH_TOP_FRONT_CENTER (1ULL << AV_CHAN_TOP_FRONT_CENTER )
> +#define AV_CH_TOP_FRONT_RIGHT (1ULL << AV_CHAN_TOP_FRONT_RIGHT )
> +#define AV_CH_TOP_BACK_LEFT (1ULL << AV_CHAN_TOP_BACK_LEFT )
> +#define AV_CH_TOP_BACK_CENTER (1ULL << AV_CHAN_TOP_BACK_CENTER )
> +#define AV_CH_TOP_BACK_RIGHT (1ULL << AV_CHAN_TOP_BACK_RIGHT )
> +#define AV_CH_STEREO_LEFT (1ULL << AV_CHAN_STEREO_LEFT )
> +#define AV_CH_STEREO_RIGHT (1ULL << AV_CHAN_STEREO_RIGHT )
> +#define AV_CH_WIDE_LEFT (1ULL << AV_CHAN_WIDE_LEFT )
> +#define AV_CH_WIDE_RIGHT (1ULL << AV_CHAN_WIDE_RIGHT )
> +#define AV_CH_SURROUND_DIRECT_LEFT (1ULL << AV_CHAN_SURROUND_DIRECT_LEFT )
> +#define AV_CH_SURROUND_DIRECT_RIGHT (1ULL << AV_CHAN_SURROUND_DIRECT_RIGHT)
> +#define AV_CH_LOW_FREQUENCY_2 (1ULL << AV_CHAN_LOW_FREQUENCY_2 )
>
> +#if FF_API_OLD_CHANNEL_LAYOUT
> /** Channel mask value used for AVCodecContext.request_channel_layout
> to indicate that the user requests the channel order of the decoder output
> - to be the native codec channel order. */
> + to be the native codec channel order.
> + @deprecated channel order is now indicated in a special field in
> + AVChannelLayout
> + */
> #define AV_CH_LAYOUT_NATIVE 0x8000000000000000ULL
> +#endif
>
> /**
> * @}
> @@ -122,6 +184,135 @@ enum AVMatrixEncoding {
> AV_MATRIX_ENCODING_NB
> };
>
> +/**
> + * An AVChannelLayout holds information about the channel layout of audio data.
> + *
> + * A channel layout here is defined as a set of channels ordered in a specific
> + * way (unless the channel order is AV_CHANNEL_ORDER_UNSPEC, in which case an
> + * AVChannelLayout carries only the channel count).
> + *
> + * Unlike most structures in Libav, sizeof(AVChannelLayout) is a part of the
> + * public ABI and may be used by the caller. E.g. it may be allocated on stack.
> + * In particular, this structure can be initialized as follows:
> + * - default initialization with {0} or by setting all used fields correctly
> + * - with predefined layout as initializer (AV_CHANNEL_LAYOUT_STEREO, etc.)
> + * - with a constructor function such as av_channel_layout_default()
> + * On that note, this also applies:
> + * - copy via assigning is forbidden, av_channel_layout_copy() must be used
> + * instead (and its return value should be checked)
> + * - if order is AV_CHANNEL_ORDER_CUSTOM, then it must be uninitialized with
> + * av_channel_layout_uninit().
> + *
> + * No new fields may be added to it without a major version bump, except for
> + * new elements of the union fitting in sizeof(uint64_t).
> + *
> + * An AVChannelLayout can be constructed using the convenience function
> + * av_channel_layout_from_mask() / av_channel_layout_from_string(), or it can be
> + * built manually by the caller.
> + */
> +typedef struct AVChannelLayout {
> + /**
> + * Channel order used in this layout.
> + * This is a mandatory field, will default to AV_CHANNEL_ORDER_NATIVE.
> + */
> + enum AVChannelOrder order;
> +
> + /**
> + * Number of channels in this layout. Mandatory field.
> + */
> + int nb_channels;
This should be unsigned.
> +
> + /**
> + * Details about which channels are present in this layout.
> + * For AV_CHANNEL_ORDER_UNSPEC, this field is undefined and must not be
> + * used.
> + */
> + union {
> + /**
> + * This member must be used for AV_CHANNEL_ORDER_NATIVE.
> + * It is a bitmask, where the position of each set bit means that the
> + * AVChannel with the corresponding value is present.
> + *
> + * I.e. when (mask & (1 << AV_CHAN_FOO)) is non-zero, then AV_CHAN_FOO
> + * is present in the layout. Otherwise it is not present.
> + *
> + * @note when a channel layout using a bitmask is constructed or
> + * modified manually (i.e. not using any of the av_channel_layout_*
> + * functions), the code doing it must ensure that the number of set bits
> + * is equal to nb_channels.
> + */
> + uint64_t mask;
> + /**
> + * This member must be used when the channel order is
> + * AV_CHANNEL_ORDER_CUSTOM. It is a nb_channels-sized array, with each
> + * element signalling the presend of the AVChannel with the
> + * corresponding value.
> + *
> + * I.e. when map[i] is equal to AV_CHAN_FOO, then AV_CH_FOO is the i-th
> + * channel in the audio data.
> + */
> + enum AVChannel *map;
> + } u;
> +} AVChannelLayout;
> +
> +#define AV_CHANNEL_LAYOUT_MONO \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 1, .u = { .mask = AV_CH_LAYOUT_MONO }}
Does this mean that named fields is no longer an issue with any of the
supported compilers?
> +#define AV_CHANNEL_LAYOUT_STEREO \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 2, .u = { .mask = AV_CH_LAYOUT_STEREO }}
> +#define AV_CHANNEL_LAYOUT_2POINT1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 3, .u = { .mask = AV_CH_LAYOUT_2POINT1 }}
> +#define AV_CHANNEL_LAYOUT_2_1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 3, .u = { .mask = AV_CH_LAYOUT_2_1 }}
> +#define AV_CHANNEL_LAYOUT_SURROUND \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 3, .u = { .mask = AV_CH_LAYOUT_SURROUND }}
> +#define AV_CHANNEL_LAYOUT_3POINT1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4, .u = { .mask = AV_CH_LAYOUT_3POINT1 }}
> +#define AV_CHANNEL_LAYOUT_4POINT0 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4, .u = { .mask = AV_CH_LAYOUT_4POINT0 }}
> +#define AV_CHANNEL_LAYOUT_4POINT1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 5, .u = { .mask = AV_CH_LAYOUT_4POINT1 }}
> +#define AV_CHANNEL_LAYOUT_2_2 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4, .u = { .mask = AV_CH_LAYOUT_2_2 }}
> +#define AV_CHANNEL_LAYOUT_QUAD \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 4, .u = { .mask = AV_CH_LAYOUT_QUAD }}
> +#define AV_CHANNEL_LAYOUT_5POINT0 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 5, .u = { .mask = AV_CH_LAYOUT_5POINT0 }}
> +#define AV_CHANNEL_LAYOUT_5POINT1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6, .u = { .mask = AV_CH_LAYOUT_5POINT1 }}
> +#define AV_CHANNEL_LAYOUT_5POINT0_BACK \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 5, .u = { .mask = AV_CH_LAYOUT_5POINT0_BACK }}
> +#define AV_CHANNEL_LAYOUT_5POINT1_BACK \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6, .u = { .mask = AV_CH_LAYOUT_5POINT1_BACK }}
> +#define AV_CHANNEL_LAYOUT_6POINT0 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6, .u = { .mask = AV_CH_LAYOUT_6POINT0 }}
> +#define AV_CHANNEL_LAYOUT_6POINT0_FRONT \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6, .u = { .mask = AV_CH_LAYOUT_6POINT0_FRONT }}
> +#define AV_CHANNEL_LAYOUT_HEXAGONAL \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 6, .u = { .mask = AV_CH_LAYOUT_HEXAGONAL }}
> +#define AV_CHANNEL_LAYOUT_6POINT1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7, .u = { .mask = AV_CH_LAYOUT_6POINT1 }}
> +#define AV_CHANNEL_LAYOUT_6POINT1_BACK \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7, .u = { .mask = AV_CH_LAYOUT_6POINT1_BACK }}
> +#define AV_CHANNEL_LAYOUT_6POINT1_FRONT \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7, .u = { .mask = AV_CH_LAYOUT_6POINT1_FRONT }}
> +#define AV_CHANNEL_LAYOUT_7POINT0 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7, .u = { .mask = AV_CH_LAYOUT_7POINT0 }}
> +#define AV_CHANNEL_LAYOUT_7POINT0_FRONT \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 7, .u = { .mask = AV_CH_LAYOUT_7POINT0_FRONT }}
> +#define AV_CHANNEL_LAYOUT_7POINT1 \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8, .u = { .mask = AV_CH_LAYOUT_7POINT1 }}
> +#define AV_CHANNEL_LAYOUT_7POINT1_WIDE \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8, .u = { .mask = AV_CH_LAYOUT_7POINT1_WIDE }}
> +#define AV_CHANNEL_LAYOUT_7POINT1_WIDE_BACK \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8, .u = { .mask = AV_CH_LAYOUT_7POINT1_WIDE_BACK }}
> +#define AV_CHANNEL_LAYOUT_OCTAGONAL \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 8, .u = { .mask = AV_CH_LAYOUT_OCTAGONAL }}
> +#define AV_CHANNEL_LAYOUT_HEXADECAGONAL \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 16, .u = { .mask = AV_CH_LAYOUT_HEXAGONAL }}
> +#define AV_CHANNEL_LAYOUT_STEREO_DOWNMIX \
> + { .order = AV_CHANNEL_ORDER_NATIVE, .nb_channels = 2, .u = { .mask = AV_CH_LAYOUT_STEREO_DOWNMIX }}
> +
<snip deprecating stuff>
> +
> +/**
> + * This is the inverse function of @ref av_channel_from_string().
> + *
> + * @return a string describing a given channel, "?" if not found.
AFAIR, none of our other get_name()-style API return "?" if not found,
they all return NULL and let the application set a substitution string.
Let us make this API consistent.
> + */
> +const char *av_channel_name(enum AVChannel channel);
> +
> +/**
> + * This is the inverse function of @ref av_channel_name().
> + *
> + * @return a channel described by the given string, or a negative AVERROR value.
> + */
> +int av_channel_from_string(const char *name);
If it is really the exact inverse of av_channel_name(), then it should
be av_channel_from_name(). If it accepts other syntaxes too, then they
should be documented.
> +
> +/**
> + * Initialize a native channel layout from a bitmask indicating which channels
> + * are present.
> + *
> + * @note channel_layout should be properly allocated as described above.
> + *
> + * @param channel_layout the layout structure to be initialized
> + * @param mask bitmask describing the channel layout
> + */
> +void av_channel_layout_from_mask(AVChannelLayout *channel_layout, uint64_t mask);
> +
> +/**
> + * Initialize a channel layout from a given string description.
> + * The input string can be represented by:
> + * - the formal channel layout name (returned by av_channel_layout_describe())
> + * - single or multiple channel names (returned by av_channel_name()
> + * or concatenated with "|")
> + * - a hexadecimal value of a channel layout (eg. "0x4")
> + * - the number of channels with default layout (eg. "5")
> + * - the number of unordered channels (eg. "4 channels")
av_get_channel_layout() used to use '+' instead of '|', and I think it
is better. For once, '+' is not a special character for shells.
> + *
> + * @note channel_layout should be properly allocated as described above.
> + *
> + * @param channel_layout input channel layout
> + * @param str string describing the channel layout
> + * @return 0 channel layout was detected, AVERROR_INVALIDATATA otherwise
> + */
> +int av_channel_layout_from_string(AVChannelLayout *channel_layout,
> + const char *str);
> +
> +/**
> + * Get the default channel layout for a given number of channels.
> + *
> + * @note channel_layout should be properly allocated as described above.
> + *
> + * @param channel_layout the layout structure to be initialized
> + * @param nb_channels number of channels
> + */
> +void av_channel_layout_default(AVChannelLayout *ch_layout, int nb_channels);
unsigned channels
> +
> +/**
> + * Free any allocated data in the channel layout and reset the channel
> + * count to 0.
> + *
> + * @note this only used for structure initialization and for freeing the
> + * allocated memory for AV_CHANNEL_ORDER_CUSTOM order.
> + *
> + * @param channel_layout the layout structure to be uninitialized
> + */
> +void av_channel_layout_uninit(AVChannelLayout *channel_layout);
> +
> +/**
> + * Make a copy of a channel layout. This differs from just assigning src to dst
> + * in that it allocates and copies the map for AV_CHANNEL_ORDER_CUSTOM.
> + *
> + * @note the destination channel_layout will be always uninitialized before copy.
> + *
> + * @param dst destination channel layout
> + * @param src source channel layout
> + * @return 0 on success, a negative AVERROR on error.
> + */
> +int av_channel_layout_copy(AVChannelLayout *dst, const AVChannelLayout *src);
> +
> +/**
> + * Get a human-readable string describing the channel layout properties.
> + *
> + * @note The returned string is allocated with av_malloc(),
> + * and must be freed by the caller with av_free().
> + *
> + * @param channel_layout channel layout to be described
> + * @return a string describing the structure or NULL on failure in the same
> + * format that is accepted by @ref av_channel_layout_from_string().
> + */
> +char *av_channel_layout_describe(const AVChannelLayout *channel_layout);
There should also be av_channel_layout_describe_to_bprint() to let the
user control the buffer allocation with more ease.
> +
> +/**
> + * Get the channel with the given index in a channel layout.
> + *
> + * @param channel_layout input channel layout
> + * @return channel with the index idx in channel_layout on success or a negative
> + * AVERROR on failure (if idx is not valid or the channel order
> + * is unspecified)
> + */
> +int av_channel_layout_get_channel(const AVChannelLayout *channel_layout, int idx);
> +
> +/**
> + * Get the index of a given channel in a channel layout. In case multiple
> + * channels are found, only the first match will be returned.
> + *
> + * @param channel_layout input channel layout
> + * @return index of channel in channel_layout on success or a negative number if
> + * channel is not present in channel_layout.
> + */
> +int av_channel_layout_channel_index(const AVChannelLayout *channel_layout,
> + enum AVChannel channel);
> +
> +/**
> + * Find out what channels from a given set are present in a channel layout,
> + * without regard for their positions.
> + *
> + * @param channel_layout input channel layout
> + * @param mask a combination of AV_CH_* representing a set of channels
> + * @return a bitfield representing all the channels from mask that are present
> + * in channel_layout
> + */
> +uint64_t av_channel_layout_subset(const AVChannelLayout *channel_layout,
> + uint64_t mask);
> +
> +/**
> + * Check whether a channel layout is valid, i.e. can possibly describe audio
> + * data.
> + *
> + * @param channel_layout input channel layout
> + * @return 1 if channel_layout is valid, 0 otherwise.
> + */
> +int av_channel_layout_check(const AVChannelLayout *channel_layout);
> +
> +/**
> + * Check whether two channel layouts are semantically the same, i.e. the same
> + * channels are present on the same positions in both.
> + *
> + * If one of the channel layouts is AV_CHANNEL_ORDER_UNSPEC, while the other is
> + * not, they are considered to be unequal. If both are AV_CHANNEL_ORDER_UNSPEC,
> + * they are considered equal iff the channel counts are the same in both.
> + *
> + * @param chl input channel layout
> + * @param chl1 input channel layout
> + * @return 0 if chl and chl1 are equal, 1 if they are not equal. A negative
> + * AVERROR code if one or both are invalid.
> + */
> +int av_channel_layout_compare(const AVChannelLayout *chl, const AVChannelLayout *chl1);
> +
> /**
> * @}
> * @}
No more remarks for the first round of review.
Regards,
--
Nicolas George
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