libctx, 
                               const char *propq);
int OSSL_DECODER_CTX_get_num_decoders(OSSL_DECODER_CTX *ctx);

typedef struct ossl_decoder_instance_st OSSL_DECODER_INSTANCE;
OSSL_DECODER *
OSSL_DECODER_INSTANCE_get_decoder(OSSL_DECODER_INSTANCE *decoder_inst);
void *
OSSL_DECODER_INSTANCE_get_decoder_ctx(OSSL_DECODER_INSTANCE *decoder_inst);
const char *
OSSL_DECODER_INSTANCE_get_input_type(OSSL_DECODER_INSTANCE *decoder_inst);
OSSL_DECODER_INSTANCE_get_input_structure(OSSL_DECODER_INSTANCE *dec