Unit types are split into three categories, depending on how their
content is managed:
* POD structure - these require no special treatment.
* Structure containing references to refcounted buffers - these can use
a common free function when the offsets of all the internal references
are known.
* More complex structures - these still require ad-hoc treatment.
For each codec we can then maintain a table of descriptors for each set of
equivalent unit types, defining the mechanism needed to allocate/free that
unit content. This is not required to be used immediately - a new alloc
function supports this, but does not replace the old one which works without
referring to these tables.
---
I switched to a fixed-size array of unit types in each descriptor to handle the
case where multiple types need the same handling. I wonder whether that might
be better as a pointer, using a compound literal array in each entry - any
opinion on that?
libavcodec/cbs.c | 63 +++++++++++++++++++++++++++++++++++++++
libavcodec/cbs.h | 9 ++++++
libavcodec/cbs_internal.h | 42 ++++++++++++++++++++++++++
3 files changed, 114 insertions(+)
diff --git a/libavcodec/cbs.c b/libavcodec/cbs.c
index 1a43cd2694..57f0c2257a 100644
--- a/libavcodec/cbs.c
+++ b/libavcodec/cbs.c
@@ -753,3 +753,66 @@ void ff_cbs_delete_unit(CodedBitstreamContext *ctx,
frag->units + position + 1,
(frag->nb_units - position) * sizeof(*frag->units));
}
+
+static void cbs_default_free_unit_content(void *opaque, uint8_t *data)
+{
+ const CodedBitstreamUnitTypeDescriptor *desc = opaque;
+ if (desc->content_type == CBS_CONTENT_TYPE_INTERNAL_REFS) {
+ int i;
+ for (i = 0; i < desc->nb_ref_offsets; i++) {
+ void **ptr = (void**)(data + desc->ref_offsets[i]);
+ av_buffer_unref((AVBufferRef**)(ptr + 1));
+ }
+ }
+ av_free(data);
+}
+
+static const CodedBitstreamUnitTypeDescriptor
+ *cbs_find_unit_type_desc(CodedBitstreamContext *ctx,
+ CodedBitstreamUnit *unit)
+{
+ const CodedBitstreamUnitTypeDescriptor *desc;
+ int i, j;
+
+ if (!ctx->codec->unit_types)
+ return NULL;
+
+ for (i = 0;; i++) {
+ desc = &ctx->codec->unit_types[i];
+ if (desc->nb_unit_types == 0)
+ break;
+ for (j = 0; j < desc->nb_unit_types; j++) {
+ if (desc->unit_types[j] == unit->type)
+ return desc;
+ }
+ }
+ return NULL;
+}
+
+int ff_cbs_alloc_unit_content2(CodedBitstreamContext *ctx,
+ CodedBitstreamUnit *unit)
+{
+ const CodedBitstreamUnitTypeDescriptor *desc;
+
+ av_assert0(!unit->content && !unit->content_ref);
+
+ desc = cbs_find_unit_type_desc(ctx, unit);
+ if (!desc)
+ return AVERROR(ENOSYS);
+
+ unit->content = av_mallocz(desc->content_size);
+ if (!unit->content)
+ return AVERROR(ENOMEM);
+
+ unit->content_ref =
+ av_buffer_create(unit->content, desc->content_size,
+ desc->content_free ? desc->content_free
+ : cbs_default_free_unit_content,
+ (void*)desc, 0);
+ if (!unit->content_ref) {
+ av_freep(&unit->content);
+ return AVERROR(ENOMEM);
+ }
+
+ return 0;
+}
diff --git a/libavcodec/cbs.h b/libavcodec/cbs.h
index be986df4e4..42896042c1 100644
--- a/libavcodec/cbs.h
+++ b/libavcodec/cbs.h
@@ -345,6 +345,15 @@ int ff_cbs_alloc_unit_content(CodedBitstreamContext *ctx,
size_t size,
void (*free)(void *opaque, uint8_t *content));
+/**
+ * Allocate a new internal content buffer matching the type of the unit.
+ *
+ * The content will be zeroed.
+ */
+int ff_cbs_alloc_unit_content2(CodedBitstreamContext *ctx,
+ CodedBitstreamUnit *unit);
+
+
/**
* Allocate a new internal data buffer of the given size in the unit.
*
diff --git a/libavcodec/cbs_internal.h b/libavcodec/cbs_internal.h
index dd4babf092..7ed8ea0049 100644
--- a/libavcodec/cbs_internal.h
+++ b/libavcodec/cbs_internal.h
@@ -25,11 +25,53 @@
#include "put_bits.h"
+enum {
+ // Unit content is a simple structure.
+ CBS_CONTENT_TYPE_POD,
+ // Unit content contains some references to other structures, but all
+ // managed via buffer reference counting. The descriptor defines the
+ // structure offsets of every buffer reference.
+ CBS_CONTENT_TYPE_INTERNAL_REFS,
+ // Unit content is something more complex. The descriptor defines
+ // special functions to manage the content.
+ CBS_CONTENT_TYPE_COMPLEX,
+};
+
+enum {
+ // Maximum number of unit types described by the same unit type
+ // descriptor.
+ CBS_MAX_UNIT_TYPES = 16,
+ // Maximum number of reference buffer offsets in any one unit.
+ CBS_MAX_REF_OFFSETS = 1,
+};
+
+typedef struct CodedBitstreamUnitTypeDescriptor {
+ int nb_unit_types;
+ const CodedBitstreamUnitType unit_types[CBS_MAX_UNIT_TYPES];
+
+ int content_type;
+ size_t content_size;
+
+ int nb_ref_offsets;
+ // The structure must contain two adjacent elements:
+ // type *field;
+ // AVBufferRef *field_ref;
+ // where field points to something in the buffer referred to by
+ // field_ref. This offset is then set to offsetof(struct, field).
+ size_t ref_offsets[CBS_MAX_REF_OFFSETS];
+
+ void (*content_free)(void *opaque, uint8_t *data);
+} CodedBitstreamUnitTypeDescriptor;
+
typedef struct CodedBitstreamType {
enum AVCodecID codec_id;
size_t priv_data_size;
+ // List of unit type descriptors for this codec.
+ // Terminated by a descriptor with nb_unit_types equal to zero.
+ const CodedBitstreamUnitTypeDescriptor *unit_types;
+
// Split frag->data into coded bitstream units, creating the
// frag->units array. Fill data but not content on each unit.
// The header argument should be set if the fragment came from
--
2.20.1
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