New VMF 3.0 API ideas

[apavlenko]

1) MetadataSchema, MetadataDesc, Metadata

• current code:

auto schema = make_shared<MetadataSchema>("schema-name", "author");
VMF_METADATA_BEGIN("channel-name");
    VMF_FIELD_STR("field1");
    VMF_FIELD_INT("field2");
VMF_METADATA_END(schema);
mdStream.addSchema(schema);
auto desc = schema->findMetadataDesc("channel-name");
auto md = std::make_shared<Metadata>(desc);
md->push_back(FieldValue("algo-id", "qqq"));
md->push_back(FieldValue("data", "qqq"));
mdStream.add(md);

• proposed code:

mdStream.addSchema(
    MetadataSchema("schema-name", "author",
        MetadataDesc("channel-name",
            FieldDesc("field1", vmf_string),
            FieldDesc("field2", vmf_integer)
        ),
        MetadataDesc(
            ...
        )
    )
);

mdStream.add(
    Metadata("channel-name",
        FieldValue("field1", "qqq"),
        FieldValue("field2", 10)
    )
);

Less code, no shared_ptr => faster!

[apavlenko]

IReader + IWriter => Format

class VMF_EXPORT Format
{
public:

    typedef std::map<std::string, std::string> AttribMap;
    /*!
    * \brief Export various metadata stream items to a string representation. Used in particular for "stream.serialize()" implementation.
    */
    virtual std::string store(
        const MetadataSet& set,
        const std::vector<std::shared_ptr<MetadataSchema>>& schemas = {},
        const std::vector<std::shared_ptr<MetadataStream::VideoSegment>>& segments = {},
        const std::vector<Stat>& stats = {},
        const AttribMap& attribs = {} // nextId, checksum, etc
        ) = 0;

    /*!
    * \brief Deserialize input string to stream metadata and related stuff. Used in particular for "stream.deserialize(text)" implementation.
    */
    virtual std::array<int, 5> parse(
        const std::string& text,
        std::vector<std::shared_ptr<MetadataInternal>>& metadata,
        std::vector<std::shared_ptr<MetadataSchema>>& schemas,
        std::vector<std::shared_ptr<MetadataStream::VideoSegment>>& segments,
        std::vector<Stat>& stats,
        AttribMap& attribs // nextId, checksum, etc
        ) = 0;
;

Simpler API.