[FFmpeg-devel] [PATCH v2 06/11] cbs: Add support functions for handling unit content references
James Almer
jamrial at gmail.com
Wed May 22 00:20:04 EEST 2019
On 5/20/2019 8:02 PM, Mark Thompson wrote:
> Use the unit type table to determine what we need to do to clone the
> internals of the unit content when making copies for refcounting or
> writeability. (This will still fail for units with complex content
> if they do not have a defined clone function.)
>
> Setup and naming from a patch by Andreas Rheinhardt
> <andreas.rheinhardt at googlemail.com>, but with the implementation
> changed to use the unit type information if possible rather than
> requiring a codec-specific function.
> ---
> libavcodec/cbs.c | 168 ++++++++++++++++++++++++++++++++++++++
> libavcodec/cbs.h | 23 ++++++
> libavcodec/cbs_internal.h | 1 +
> 3 files changed, 192 insertions(+)
>
> diff --git a/libavcodec/cbs.c b/libavcodec/cbs.c
> index 1963d86133..9fc8e1eb47 100644
> --- a/libavcodec/cbs.c
> +++ b/libavcodec/cbs.c
> @@ -816,3 +816,171 @@ int ff_cbs_alloc_unit_content2(CodedBitstreamContext *ctx,
>
> return 0;
> }
> +
> +static int cbs_clone_unit_content(AVBufferRef **clone_ref,
> + CodedBitstreamUnit *unit,
> + const CodedBitstreamUnitTypeDescriptor *desc)
> +{
> + uint8_t *src, *copy;
> + void **src_ptr, **copy_ptr;
Why use void if you're going to cast these to uint8_t everywhere?
> + AVBufferRef **src_buf, **copy_buf;
> + int err, i;
> +
> + av_assert0(unit->type == desc->unit_type);
> + av_assert0(unit->content);
> + src = unit->content;
> +
> + copy = av_malloc(desc->content_size);
> + if (!copy) {
> + err = AVERROR(ENOMEM);
> + goto fail;
> + }
> + memcpy(copy, src, desc->content_size);
> +
> + for (i = 0; i < desc->nb_ref_offsets; i++) {
> + src_ptr = (void**)(src + desc->ref_offsets[i]);
> + src_buf = (AVBufferRef**)(src_ptr + 1);
> + copy_ptr = (void**)(copy + desc->ref_offsets[i]);
> + copy_buf = (AVBufferRef**)(copy_ptr + 1);
> +
> + if (!*src_ptr) {
> + av_assert0(!*src_buf);
> + continue;
> + }
> + if (!*src_buf) {
> + // We can't handle a non-refcounted pointer here - we don't
> + // have enough information to handle whatever structure lies
> + // at the other end of it.
> + err = AVERROR(EINVAL);
> + goto fail;
> + }
> +
> + // src_ptr is required to point somewhere inside src_buf. If it
> + // doesn't, there is a bug somewhere.
> + av_assert0((uint8_t*)*src_ptr >= (*src_buf)->data &&
> + (uint8_t*)*src_ptr < (*src_buf)->data + (*src_buf)->size);
> +
> + *copy_buf = av_buffer_ref(*src_buf);
> + if (!*copy_buf) {
> + err = AVERROR(ENOMEM);
> + goto fail;
> + }
> +
> + err = av_buffer_make_writable(copy_buf);
> + if (err < 0) {
> + av_buffer_unref(copy_buf);
> + goto fail;
> + }
Maybe instead of buffer_ref + make_writable, just do a buffer_alloc +
memcpy. It should be faster and only requires one failure check.
> +
> + *copy_ptr = (*copy_buf)->data +
> + ((uint8_t*)*src_ptr - (*src_buf)->data);
> + }
> +
> + *clone_ref = av_buffer_create(copy, desc->content_size,
> + desc->content_free ? desc->content_free :
> + cbs_default_free_unit_content,
> + (void*)desc, 0);
> + if (!*clone_ref)
> + goto fail;
> +
> + return 0;
> +
> +fail:
> + for (--i; i >= 0; i--)
> + av_buffer_unref((AVBufferRef**)(copy + desc->ref_offsets[i]));
> + av_freep(©);
> + *clone_ref = NULL;
> + return err;
> +}
> +
> +int ff_cbs_make_unit_refcounted(CodedBitstreamContext *ctx,
> + CodedBitstreamUnit *unit)
> +{
> + const CodedBitstreamUnitTypeDescriptor *desc;
> + AVBufferRef *ref;
> + int err;
> +
> + if (unit->content_ref)
> + return 0;
> +
> + desc = cbs_find_unit_type_desc(ctx, unit);
> + if (!desc)
> + return AVERROR(ENOSYS);
> +
> + switch (desc->content_type) {
> + case CBS_CONTENT_TYPE_POD:
> + ref = av_buffer_alloc(desc->content_size);
> + if (!ref)
> + return AVERROR(ENOMEM);
> + memcpy(ref->data, unit->content, desc->content_size);
> + err = 0;
> + break;
> +
> + case CBS_CONTENT_TYPE_INTERNAL_REFS:
> + err = cbs_clone_unit_content(&ref, unit, desc);
> + break;
> +
> + case CBS_CONTENT_TYPE_COMPLEX:
> + if (!desc->content_clone)
> + return AVERROR_PATCHWELCOME;
> + err = desc->content_clone(&ref, unit);
> + break;
> +
> + default:
> + av_assert0(0 && "Invalid content type.");
> + }
> +
> + if (err < 0)
> + return err;
> +
> + av_buffer_unref(&unit->content_ref);
> + unit->content_ref = ref;
> + unit->content = ref->data;
> + return 0;
> +}
> +
> +int ff_cbs_make_unit_writable(CodedBitstreamContext *ctx,
> + CodedBitstreamUnit *unit)
> +{
> + const CodedBitstreamUnitTypeDescriptor *desc;
> + AVBufferRef *ref;
> + int err;
> +
> + // This can only be applied to refcounted units.
> + err = ff_cbs_make_unit_refcounted(ctx, unit);
> + if (err < 0)
> + return err;
> + av_assert0(unit->content && unit->content_ref);
> +
> + if (av_buffer_is_writable(unit->content_ref))
> + return 0;
> +
> + desc = cbs_find_unit_type_desc(ctx, unit);
> + if (!desc)
> + return AVERROR(ENOSYS);
> +
> + switch (desc->content_type) {
> + case CBS_CONTENT_TYPE_POD:
> + return av_buffer_make_writable(&unit->content_ref);
> +
> + case CBS_CONTENT_TYPE_INTERNAL_REFS:
> + err = cbs_clone_unit_content(&ref, unit, desc);
> + break;
> +
> + case CBS_CONTENT_TYPE_COMPLEX:
> + if (!desc->content_clone)
> + return AVERROR_PATCHWELCOME;
> + err = desc->content_clone(&ref, unit);
> + break;
> +
> + default:
> + av_assert0(0 && "Invalid content type.");
> + }
> + if (err < 0)
> + return err;
> +
> + av_buffer_unref(&unit->content_ref);
> + unit->content_ref = ref;
> + unit->content = ref->data;
> + return 0;
> +}
> diff --git a/libavcodec/cbs.h b/libavcodec/cbs.h
> index 8f764905bd..f5d2dcdb08 100644
> --- a/libavcodec/cbs.h
> +++ b/libavcodec/cbs.h
> @@ -396,4 +396,27 @@ int ff_cbs_delete_unit(CodedBitstreamContext *ctx,
> int position);
>
>
> +/**
> + * Make the content of a unit refcounted.
> + *
> + * If the unit is not refcounted, this will do a deep copy of the unit
> + * content to new refcounted buffers.
> + */
> +int ff_cbs_make_unit_refcounted(CodedBitstreamContext *ctx,
> + CodedBitstreamUnit *unit);
> +
> +/**
> + * Make the content of a unit writable so that internal fields can be
> + * modified.
> + *
> + * If it is known that there are no other references to the content of
> + * the unit, does nothing and returns success. Otherwise (including the
> + * case where the unit content is not refcounted), it does a full clone
> + * of the content (including any internal buffers) to make a new copy,
> + * and replaces the existing references inside the unit with that.
> + */
> +int ff_cbs_make_unit_writable(CodedBitstreamContext *ctx,
> + CodedBitstreamUnit *unit);
> +
> +
> #endif /* AVCODEC_CBS_H */
> diff --git a/libavcodec/cbs_internal.h b/libavcodec/cbs_internal.h
> index 439fa7934b..194adc42c1 100644
> --- a/libavcodec/cbs_internal.h
> +++ b/libavcodec/cbs_internal.h
> @@ -55,6 +55,7 @@ typedef struct CodedBitstreamUnitTypeDescriptor {
> size_t ref_offsets[CBS_MAX_REF_OFFSETS];
>
> void (*content_free)(void *opaque, uint8_t *data);
> + int (*content_clone)(AVBufferRef **ref, CodedBitstreamUnit *unit);
Wouldn't implementing this directly in AVBufferRef be a better idea
instead? Right now it only supports flat data arrays, and having a
callback function that gets called when av_buffer_make_writable() makes
a copy of the buffer would allow us to also have complex structures,
with pointers or even other AVBufferRefs as well.
The relevant CBS changes from this patch would then be much simpler, and
it would also solve things like the decoupled qp_table frame side data
types, or how a copy of the entire raw sps is embedded in struct sps in
h264_ps.h as a 4kb array.
> } CodedBitstreamUnitTypeDescriptor;
>
> typedef struct CodedBitstreamType {
>
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